Local controls

Local adjustments - Lab

(16 november 2020)

Contents

1 Introduction

Local editing in RawTherapee is based on RT-spots, which are similar in principle to the U-Point concept originally used in Nikon Capture NX2 © and subsequently in the Nik Collection ©, DxO PhotoLab © and Capture NXD ©. RT-spots use algorithms developed specifically for RawTherapee by Jacques Desmis.

This approach is completely different to the more familiar local editing methods used in applications such as the GIMP, Photoshop © etc., which primarily use selection tools such as lassos, magic wands etc., associated with brushes, layers and blend masks. These methods can be time consuming and difficult to use accurately when complex shapes are involved.


An RT-spot consists of either an ellipse or a rectangle with a variable-diameter spot at the center. The shapes have four control points, which can be adjusted independently or symmetrically, and future developments will provide enhanced shape manipulation.


The RT-spot algorithm uses shape detection based on ΔE (the change in the visual perception of two given colours) to select the parts of the image to be modified inside the ellipse or rectangle. The extent to which these modifications are applied can be finely controlled allowing for very precise selections. Further refinement is possible with additional parametric masks but the shape-detection algorithms should be sufficient for the vast majority of local editing requirements. RT-spots can also be used in ‘Excluding’ mode to prevent the algorithm from influencing certain parts of the image. The modifications that can be carried out are extensive and incorporate most of the functions available in RawTherapee’s global adjustment tools along with some additional tools available only in the Local Adjustment tab.


The tools are grouped in the following modules (Tool name - position in pipeline):

1.1 Color & Light - 11

Adjust color, lightness, contrast and correct small defects such as red-eye, sensor dust etc. Other functions include a graduated filter, L*a*b* curves and blend modes.

1.2 Shadows/Highlights & Tone Equalizer - 5

Adjust shadows & highlights either with the shadows/highlights sliders or with a tone equalizer. Can be used instead of, or in conjunction with the Exposure module. Can also be used as a graduated filter.

1.3 Vibrance & Warm/Cool - 3

Adjust vibrance (essentially the same as the global adjustment). Carry out the equivalent of a white-balance adjustment using a CIECAM algorithm.

1.4 Log Encoding - 0

Adjust underexposed or high-dynamic-range images using a log-encoded algorithm.

1.5 Dynamic Range & Exposure - 10

Modify exposure in L*a*b* space using Laplacian PDE algorithms to take into account dE and minimize artifacts. Laplacian operators are used because they are particularly good at detecting fine details but you do not need to understand how they work to use this tool!

1.6 Common Color Mask - 13

A tool in its own right. Can be used to adjust the image appearance (chrominance, luminance, contrast) and texture as a function of Scope.

1.7 Soft Light & Original Retinex - 6

Apply a Soft-light blend (identical to the global adjustment). Carry out dodge and burn using the original Retinex algorithm.

1.8 Blur/Grain & Denoise - 1

Can be used to blur backgrounds, soften skin, add film grain and denoise.

1.9 Tone Mapping - 4

Same as the tone mapping tool in the main menu. The main menu tool must be deactivated if this tool is used.

1.10 Dehaze & Retinex - 9

Dehaze and Retinex (Advanced mode only). Useful for dehaze, local contrast with high values and simulation of ‘clarity’.

1.11 Sharpening - 8

Uses RL deconvolution sharpening. View at 1:1

1.12 Local Contrast & Wavelets - 7

  • Local Contrast: basically the same functions as “Local Contrast” in the “Detail” tab
  • Wavelets: based on “Wavelet Levels” in the “Advanced” tab with essentially the same features (clarity, contrast, blur, etc., see documentation). Its use in “Local Adjustments” provides additional possibilities such as the removal of large blemishes, grease stains etc.

1.13 CBDL - 2

Contrast by detail levels. Can be used to remove sensor or lens marks.


Each tool module can be toggled between Basic, Standard & Advanced modes. The default mode can be set in RawTherapee’s Preferences window.

The examples in the next section are designed to give a brief overview of some of the ways the various tools can be used for local adjustments. However, if you prefer to explore the possibilities by yourself, then try setting the ‘Default complexity for Local Adjustments’ in the Preferences module to “Basic” and uncheck the “Show additional settings” checkbox at the top of the Local Adjustments module. This will give you a simplified yet powerful version of Local Adjustments.

Explore the capabilities of the “Color & Light”, “Shadows/Highlights & Tone Equalizer” and “Vibrance & Warm/Cool” tools to start with and don’t hesitate to try out the additional functionality by manually setting the complexity mode to “Standard” (in the combobox in the module you are working on). The “Color & Light” tool is extremely powerful and includes functions from both the “Color Toning>Color correction regions” module in the main-menu Color tab as well as the L*a*b* curves available in the Exposure tab.


2 Getting started

Please note: The screenshots in the following examples are currently being updated to take into account the latest developments. Because of this, some of the slider and module names will be different from the text.

2.1 Activating local adjustments

  • In the tab bar, select the "hand" icon (Local Adjustments tab)
  • Turn on the "Local Adjustments" power button (if it is not already activated) and expand the "Settings” module.
  • Select "Add"
    Original











2.2 Preparation

Position the RT-spot at the desired location. In this case, we want to increase the saturation of the red flower and reduce the luminance (lightness) without affecting the rest of the image:

  • Move the center of the RT-spot so that it is located on an area representative of what you want to change.
  • Position the 4 delimiters well beyond the flower.
  • Select the "Lockable Color Picker" and locate 3 colors: a) one on the red flower, b) one on the blue sky, c) one on a green leaf.
  • In the example the 3 colors are:
    • red flower L=48.6 a=74.4 b=47.0
    • blue sky : L=68.6 a=-3.1 b=-16.6
    • green leaf : L=48.3 a=-28.3 b=51.4
Preparation

Raw file: [1]










2.3 Adding the Color & Light tool

In the settings menu, choose "Add tool to current spot".

  • You will see a list of choices : "Color & Light - 11",..., "Log Encoding – 0" etc.. For each RT-spot you can associate 1 or more tools from the list. The processing order in the pipeline corresponds to the number at the end of the tool description : "Log Encoding - 0" is first (if it is activated), "Color & Light -11" is the last one. This is also the case for the associated masks.
  • Select "Color&Light - 11"
Adding the Color & Light tool

















2.4 Adjusting luminance (lightness) and chrominance

  • Set "Lightness" to -70
  • Set "Chrominance" to 130
  • Review the results
  • The red flower now has a new color L= 41.3, a = 66.0, b = 50.4
  • the sky is unchanged
  • the green leaf is unchanged
Adjusting luminance (lightness) and chrominance




















2.5 Color Tool Scope and Transition Value

In the "Settings" module

  • Observe the effect of moving the "Scope (color tools)" slider
    • if you reduce the value (default 30) only a part of the reds will be affected.
    • if you increase the value, the sky, then the green leaf, then the whole image will be taken into account (Scope=100)

Leave the Scope value at 100 and in the "Settings" module select "Show additional settings"

  • Observe the effect of moving the "Transition value" slider:
    • reduce the value to 5
    • increase the value to 100 and see the result

2.6 Previewing the adjustment area using deltaE (ΔE)

You can preview the areas of the image that will be affected by any changes. The preview does not show the changes themselves or the transitions, but allows you to set the scope of any adjustments. There are two possibilities:

  • Use the "Preview ΔE" button located in "Settings". This will only work if you have activated one (and only one) of the tools in "Add tool to current spot" menu.
  • Use the "Preview ΔE" option in the "Mask and modifications" menu associated with a particular tool (standard and advanced modes only). In this case the GUI takes into account any adjustments made with the tool and works regardless of the number of activated tools.


You can vary the intensity and color of this preview with "ΔE preview color " in the "Shape detection" section of the "Settings" module . The preview will also let you see the effect of varying the other sliders in the Shape detection section.

Previewing the modifiable area










2.7 Viewing the changes

To see the changes :

  • Go to "Mask and modifications" > "Show modifications without mask" (don’t forget to select either “Standard” or “Advanced” in the “Color & Light” combobox) .
  • You can see the effects of any changes to luminance, contrast, color and saturation, as well as any changes to the texture or structure of the image.
  • You can also see the effect of the transition settings:
    • "Transition value": percentage of the area that will receive the full effect of any adjustments before dropping off to zero.
    • "Transition decay": the rate with which the zone of influence decreases
    • "Transition differentiation XY": difference in coverage between abscissa and ordinate


Try out the following and observe the effect:

  • Change the "Scope (color tools)". Remember that the scope slider acts on deltaE
  • Transition settings
  • Tool settings (luminance, chroma, etc.)
Viewing the modified areas













2.8 Work on the full image using an "excluding" spot

Local adjustments are not limited to local touch-ups. You can also use the Local Adjustment tools to process the full image. Currently you have to expand a rectangular spot manually to cover the image completely but this will be done automatically in future versions.

In "Settings" enable "Show additional settings":

  • Set the "RT-spot shape" to a rectangle
  • Position the 4 delimiters outside of the preview
  • Set the transition to 100 (or another value if you wish to generate a gradient, bearing in mind that there are other tools for making gradients). You are now ready to use all the tools in full-image mode
Working on the complete image - settings










2.9 Example: changing the color of the green leaves, except for one

2.9.1 Changing the color of the leaves

  • You can use of the "a" and "b" components of "Lab" in the "Color correction grid ", by choosing "direct" (combobox under the grid) and a high value of "Strength". Moving the dots on the grid as shown will change the color of all the leaves.
  • You can adjust if necessary with "Scope (color tools)".
  • The other colors in the flower, sky etc., are not modified.
Changing the color of the leaves










.

2.9.2 Restoring the green color to one of the leaves

  • Add a second RT-spot ("Add" in the "Settings" module)
  • Choose "Spot Method” = "Excluding Spot”
  • Move the RT-spot to the leaf to be changed and expand the spot well beyond the edges of the leaf.
  • Adjust "Scope” (under the "Excluding" heading in "Settings") until you get the desired effect.
  • If you wish, you can use the "Excluding" spot in the same way as a normal RT-spot and add tools such as Denoise, Blur, etc. (i.e. it not only ‘excludes’ the effect of the adjacent spot, but it also allows you to use it in the same way as normal spot for the area it encompasses)
Using the Excluding spot












2.10 Correcting red-eye and removing sensor defects

3 steps: preparation, RT-spot adjustment, red-eye removal

2.10.1 Preparation

  • Choose a large area around the eye
  • Put the RT-spot on the red area of the eye (pupil)
  • Set 4 "Lockable color pickers" so that you can see the changes
Preparation











2.10.2 Adjusting the RT-spot

  • Add the "Color and Light" tool
  • Press the "Preview deltaE" button in "Settings" .
  • Adjust the RT-spot to obtain the desired level of selection.
    • here we have chosen to reduce the spot size = 14
    • "Scope (color tools)" = 18
Preview dE












2.10.3 Removing the red color

  • In the "Color and Light" tool, reduce the chrominance to -100
  • Observe the result :
    • the pupil of the eye has almost no dominant color anymore
    • the iris, cornea and facial skin are unchanged
    • you may need to change the "Transition value" (lower it) and "Transition decay" (increase it) in "Settings" depending on the case.
Eye with red color removed











2.10.4 Removing sensor defects or spots

The principle is the same as above for removing small sensor faults but in this example we will use different tools

  • Either CBDL (Contrast By Detail Levels),
  • Or Wavelet pyramid2 - Contrast by levels (Advanced).
  • In both cases, reduce the contrast for the lower levels of decomposition
  • Adjust "Blur levels” if necessary (wavelet pyramid1)
  • Use a low "Transition value" (less than 20) and high "Transition decay" (greater than 15)in the “Settings” module.
  • The minimum size of the RT-spot for the CBDL and Wavelet pyramid2 decomposition to function is 32x32 pixels. There are workarounds such as the use of transitions and deltaE to deal with defects smaller than the spot.

Example: removing multiple spots using wavelet pyramid2

  • Looking at the image below, we can see that it is blotchy
Multiple blotches










  • A possible solution:
    • Activate the tool "Local Contrast & Wavelets".
    • Choose "Advanced" in the first combobox and then "Wavelet" in the second combobox.
    • Adjust “Scope” to 20
    • Go to Pyramid2 and activate "Contrast by level".
    • Set high values of "Attenuation response", "Offset" and "Chroma levels" (if necessary)
    • Activate the "Contrast by level" curve and reduce the contrast for the lower levels.
Fewer blotches











2.11 Dodging and burning

In many portraits, or photos where light falls directly on the skin, an unpleasant contrast-enhancement phenomenon occurs. Some parts of the skin are slightly overexposed, while others are slightly underexposed.

  • Traditionally this problem is treated with masks and layers and there are numerous tutorials for doing this with the GIMP and Photoshop (c). You could probably use RT's "Local adjustments" masks also.
  • Here we are going to use the "Original Retinex" concept (based on Ipol research). It was developed in the 1970s and was originally designed for this sort of application and not for the way it has been subsequently used in Rawtherapee and elsewhere. We are going to:
    • use one or more adjustable-threshold Laplacian functions (see note below)
    • solve the Poisson equation (PDE - Partial Derivative Equation)
    • balance the luminance values.

Note: Laplacian operators are used because they are particularly good at detecting fine details and Poisson equations are used to solve the partial differential equation generated by the Laplacian and make the tool usable. But you do not need to understand how they work to use this tool!


There are 3 steps: preparation, Laplacian settings and preview, result

2.11.1 Preparation

  • The deltaE adjustment steps, the "Scope" (make sure you use the Original Retinex Scope) and the transition adjustment principles are identical to the previous examples and won't be repeated here.
  • The portrait we are going to use has had the eyes masked for confidentiality reasons.
  • Choose "Add tool to current spot..." : "Soft Light & Original Retinex" - "Advanced" - "Original Retinex"
Preparation











2.11.2 Adjusting the Laplacian threshold and viewing the changes

  • Adjust the "Strength" slider (which takes into account the threshold of the first Laplacian operator)
  • Adjust the "Laplacian threshold deltaE" slider (which takes into account the deltaE of the image to act on a second Laplacian operator). This processing is upstream of the Scope algorithms and can take into account differences in the background.
  • View the modifications by choosing: "Show Fourier process" : "Show modifications without mask".
Show Modifications













2.11.3 Results

Results

A similar algorithm is used in the "Dynamic Range & Exposure" tool. It can be used to process images with large differences in exposure which are often globally underexposed.











2.12 Making a graduated filter based on luminance, chrominance and hue (gradient filter)

2.12.1 Preparation

  • Choose the flower image that was used in the first example.
  • Identify 7 points with the "Lockable color picker".
  • Add the "Color and Light" tool to the current spot and select "Advanced" mode.
Preparation

Raw file: [2]











2.12.2 Making a graduated filter.

Arbitrarily we choose the following settings

  • Luminance gradient strength = -0.44
  • Chrominance gradient strength = -1.13
  • Hue gradient strength = 2.69
  • Gradient angle = -87.6
  • Scope (color tools) = 30
  • Feather gradient(settings) = 25
Luminance, Chrominance & Hue Gradient










2.12.3 Changing the default settings

  • Try to gradually change "Scope (color tools)" by increasing the value to 70, 75, 80, 85, 90, 100
  • Change "Feather gradient" in the “Settings” > “Transient Gradient” module and note the variations
  • You can also change the values of the gradients (L, C, H, angle) in the “Graduated Filter” section of the “Color & Light” tool).
  • And if you wish, the values of "Color and Light".
The settings for Transition, Gradient, Luminance, Chrominance, Hue, Scope & Feather


























2.13 Five ways to change the exposure and lift the shadows

This example is for demonstration purposes only so that we can see the various (non-exhaustive) possibilities for adjusting exposure. The settings are arbitrary.

  • The image is a difficult one with deep shadows and a central area that is almost overexposed.
  • Five possible methods are shown with arbitrary settings
    • Shadows/Highlights
    • Tone Equalizer
    • TRC (Tone Response Curve)
    • Log Encoding
    • Exposure (PDE algorithms & exposure)

We could also have used :

  • Contrast curves,
  • or lifted the shadows with "Lightness" (Color and Light),
  • or used a graduated luminance filter
  • ...

2.13.1 Preparation

  • Add a spot as shown in the image below
  • Set the "Scope (color tools)" slider to 50 (this value will be used by the "Shadows/Highlights" tool when it is added and we will use the separate "Scope" sliders for each of the “Log Encoding” and “Exposure tools”)
  • Try varying this value between 20 and 100
Lifting the shadows - preparation

Raw file: [3]












2.13.2 Using Shadows/Highlights

Add tool to current spot..."Shadows/Highlights - Tone Equalizer", “Standard”
  • Select "Shadows/Highlights" in the combobox
  • Try changing "Shadows tonal width" and "Highlights"
Lifting the shadows - Shadows Highlights











2.13.3 Using the Tone Equalizer

Add tool to current spot..."Shadows/Highlights & Tone Equalizer"
  • Select "Tone Equalizer" in the combobox
  • Try also sliders 2, 3 et 4
Lifting the shadows - Tone Equalizer











2.13.4 Using the Tone Response Curve (TRC)

Add tool to current spot..."Shadows/Highlights & Tone Equalizer"
  • Select TRC
  • Increase the "Slope" to 150 and then come back to 60
  • Try reducing and then increasing the gamma and observe the effect
Lifting the shadows - TRC











2.13.5 Using Log Encoding

Add tool to current spot..."Log Encoding"
  • Note that the "Scope" slider in this case is in the "Log Encoding"  tool: set "Scope" to 50
  • Click on the "Automatic" button
  • Adjust the "Target gray point"
Lifting the shadows – Log Encoding











2.13.6 Using Exposure

Add tool to current spot..."Dynamic Range & Exposure"

  • Select "Standard"
  • Adjust "Exposure compensation ƒ" (a Laplacian and a Fourier transform are applied)
  • Set the "Exposure Tools" sliders to: "Black" = -1500, "Shadows" = 50
  • By default "Highlight compression" is 20. Vary it to see the effect
  • Try varying the above settings
Lifting the shadows - Exposure













2.13.7 Recommendations

For portraits and images with low color contrast:

  • Use the "Exposure" slider with care because the algorithm (which is similar to the one used in the Exposure tab) is not well adapted to cases such as portraits which have subtle color variations in skin tones. The algorithm was improved recently (July 5, 2020) by the addition of a Laplacian operator to resolve the differences in contrast but it is still not the best solution for these cases.
  • Try using the "Tone equalizer" or "TRC" instead.

If you do use "Exposure", then it is recommended (but not mandatory) to change the parameters of "Shape detection" in "Settings" as follows:

  • Increase "ΔE-scope threshold"
  • Reduce "ΔE decay"
  • Set "ab-L balance (ΔE)" to L
  • Adapt "Scope (color tools)" if necessary


2.14 High dynamic range images - use Log Encoding or the "PDE" algorithms in the "Dynamic Range & Exposure" tool

2.14.1 Log Encoding and Ciecam02 Tutorial

Log encoding - Ciecam02 - Tutorial - Examples


2.14.1.1 Chromatic Adaptation Example

The first step is to find an almost mathematically perfect white balance using ‘White Balance’ > ‘Auto’ > ‘Temperature correlation’ - (same example and settings as in the 'Ciecam Advanced tab' tutorial) Raw file [4]

White Balance - Temperature correlation











2.14.1.1.1 Choose a suitable ‘Local adjustments’ setting - Preparation
  • Select the ‘Local Adjustments’ tab.
  • Add a ‘rectangle’ spot and move the delimiters well beyond the limits of the preview (so that you can move the center of the RT-spot and still cover the whole image)
  • Set the ‘Transition value’ = 100
  • Set some lockable color pickers as shown
Chromatic Adaptation - Preparation














2.14.1.1.2 Select Log encoding

Choose: ‘Add tool to current spot’ > ‘Log Encoding’

Chromatic Adaptation - Log encoding












  • Try changing the position of the center of the RT-spot
  • Try changing ‘Scope’: 40 - 60 - 80 - 100
  • Observe the results
  • Note that the image is still yellowish
2.14.1.1.3 Modify Chromatic adaptation - cat02
Chromatic Adaptation - Log encoding - Cat02












  • Make the image cooler by moving the ‘Chromatic adaptation cat02’ slider to the left.
  • Reducing the slider value by 10 units corresponds to a 300K drop in illuminant temperature.
  • Try -23
2.14.1.2 High dynamic range image + Ciecam

The image is a difficult one (the same that was used for the CIECAM in the Advanced tab). It has very marked shadows and strong sunlit backlighting. Use the default RawTherapee settings and position the lockable color pickers as shown so that you can see the changes when processing

Raw file[5]

Ciecam Lighting Preparation












2.14.1.2.1 Using Log encoding + Ciecam

Choose 'Add tool to current spot' > ‘Log Encoding’. For this example, and for comparison with Example 1 (using Source lighting), the following arbitrary settings are used:

  • Set the delimiters for the rectangular spot beyond the preview area
  • set the ‘Transition value’ = 100
  • ‘Scope’ = 79
  • ‘Level of complexity’ = ‘Advanced’
  • Press the 'Automatic' button...
Log encoding











  • Move the RT-spot and observe the effect
  • Change the ‘Scope’ settings and observe the effect


2.14.1.2.2 Adjusting the Ciecam settings in the Log Encoding module
  • For the ‘Scene Conditions’ choose ‘Surround’ = ‘Dim’. The image will become lighter.
  • In ‘Image Adjustments’, set the Saturation(s) = 30 and Contrast (J) = -10
  • Observe the effect on the shadows...
Log encoding + Ciecam saturation (s) - contraste (J) - Dim












Now open the 'All tools' expander.

  • Try Colorfulness (M) instead of Saturation (s)
  • Try Contrast (Q) instead of Contrast (J)
  • Adjust the Lightness
2.14.1.3 Log encoding - Dodge and Burn - Ciecam
2.14.1.3.1 Preparation

This is another way to Dodge and Burn using Log Encoding and Ciecam. Position the Rt-spot on the face, and set 2 ‘Lockable color pickers’ as shown

Raw file[6]

Log encoding Dodge and Burn - Preparation













2.14.1.3.2 Using Log encoding in manual mode with Ciecam
  • ‘Add tool to current spot’ > ‘Log Encoding’
  • Complexity = Advanced
  • Click on ‘Automatic’
  • Slightly increase the White Ev value until you get the desired effect (in this example from 3.0 to 5.0)
  • Slightly increase the Saturation (s)
  • Click on ‘All tools’ and slightly reduce Brightness (Q)
  • Try the other settings: Dim, lightness, etc.
  • You can also adjust the Scope and move the RT-spot
Log encoding Dodge and Burn - Preparation
















2.15 Other examples

High dynamic range images are one of the recurring problems in image processing. There are already several algorithms available in Rawtherapee that can be used, more or less successfully, to reduce the dynamic range: Dynamic range compression, Shadows/Highlights, Tone Equalizer, Tone Response Curve, etc.

  • In this example we are going to use the "Log Encoding" tool (derived from the darktable filmic module and adapted by A. Griggio for ART). The tool has undergone further adaptation by J. Desmis for use in Rawtherapee Local Adjustments
  • To demonstrate the possibilities of this module, we are going to use it to make a luminance gradient, without using the "Graduated filter", which is present in the "Log Encoding" menu.
  • Three steps: preparation, automatic settings, adjustments

2.15.1 Preparation

  • Set the RT-spot so that :
    • the center is at the bottom left corner of the image
    • the upper right corner is at the limits of the image
  • Go to "Add tool to current spot...". Go to "Log Encoding " (the tool has been voluntarily disabled in the screenshot)
Preparation

Raw file : [7]













2.15.2 Automatic settings

  • Press the "Automatic" button
  • The image will brighten
  • Click the "Automatic" button again to see the settings more clearly.
  • The values Black Ev = -6.7, White Ev = 6.9, indicate a large dynamic range = 13.6 EV
  • Source gray point : value (set to automatic) = 1.2
  • These settings (that you can change) are the result of calculations made upstream in the pipeline.
Automatic











2.15.3 Adjustments

You can now adapt the image to taste:

  • Play with the diagonal gradient by adjusting the "Transition Gradient" in "Settings".: "Transition value" = 45. You can also act on "Transition decay" and "Transition differentiation XY" (try it out to see how it affects the result)
  • Modify the distribution of the action inside the image by setting "Scope" (Log Encoding) = 50
  • Change the global luminance of the image by setting "Target gray point" = 22.0
Gradient and adjustments











2.15.4 Another solution using the "Dynamic Range & Exposure" tool.

We can combine two PDE algorithms used in the "Contrast attenuator" and "Dynamic range compression" options:

  • Contrast attenuator (set the values as shown in the image below) : Laplacian threshold = 75.6, Linearity = 0.61, Lapacian balance = 1.32, Gamma = 1.4
  • Dynamic range compression (set the values as shown in the image below): Amount = 65, Detail = -19, Sigma = 1.48, Offset = 2.29
  • Scope = 82
PDE Ipol - Dynamic range compression











2.16 Processing a hazy image

We are going to process a very hazy image by first applying the global "Haze Removal" tool in the "Detail" tab and then touch up the sky and horizon using local Retinex.

2.16.1 Original Image

Hazy image

Raw file: [8]











2.16.2 Processing with the Haze Removal tool (Detail tab in the main menu)

We could also have used "local dehaze" and an RT-spot. However when you look at the image there is a lot of haze in the background and the hills so it is better to use a two-step approach.

Hazy image – result with the Haze Removal tool in the main menu (Detail tab)











2.16.3 Additional processing with local Retinex

  • Choose "Add tools to current spot...". : Dehaze - Retinex - 'Advanced'
  • Try varying the settings
  • Adjust the "transmission map" curve if necessary by increasing the attenuation on the right side of the curve .
  • Now look at the hills and the sky on the horizon!
Hazy image after using Haze removal + Retinex











2.17 Using the Denoise module

Several applications are possible.
  • On selected areas to refine any denoising adjustments carried out using the denoise module in the "Detail" tab. In this case keep the denoising to a minimum in the "Detail" tab.
  • By processing the whole image using the denoise module in Local Adjustments and excluding parts of the image with an "Excluding" spot.
  • Used on its own to reduce noise in low-noise images - for example, to remove noise from the sky or a face
  • Used on its own to reduce the noise in a selected area and deliberately leave the noise in the rest of the image for artistic purposes

We are going to look at an example using this last case.

The image of the young girl is particularly noisy and has strong chromatic noise.

Denoise preparation

Raw file : [9]











2.17.1 Zoom 100%

Denoise zoom 100%











2.17.2 Which settings should we use for denoising?

  • The position of the spot and its size are important. We are going to choose a part of the face with strong chromatic noise and use a large "Spot size" for the RT-spot .
  • The choice of the "Scope" parameter is also important. In this case, where the noise occupies almost the whole color spectrum (red, green, blue, yellow), a high value of scope must be chosen (90 in this case). If on the other hand the image to be processed has mainly luminance noise, then the "usual" scope value should be chosen, i.e. around 30, to allow the algorithm to differentiate the action according to the colors.
  • There are several differences between the local adjustments denoise function and the global denoise module in the Detail tab:
    • possibility of using a curve to adjust the luminance noise level according to the level of detail (from 0 to 6 depending on the position on the abscissa of the curve).
    • a distinction is made depending on the level of detail i.e. if levels 3 and above are greater than 20% of the ordinate of the curve, the luminance noise reduction will be more aggressive.
    • the "dark - light" differentiation for luminance is handled by an "equalizer", rather than by "gamma".
    • possibility to differentiate the action between "Fine chroma" (impulse noise and low chrominance noise for levels 0 to 4) and "Coarse chroma" (packets of noise, blotches for levels 5 and 6)
    • a "red green" / "blue yellow" equalizer which can be useful for low-noise images.
    • an extra "Chroma detail recovery" slider using DCT (a Fourier-related discrete cosine transform).
    • an added "Luminance & chroma detail threshold (DCT)" slider to differentiate the action depending on the edges ("Edge detection").
Denoise settings











2.18 A moment of madness - try wavelets!

2.18.1 An example … (don't run away, it isn't as difficult as all that)

Original image, with "Exposure compensation" = +1.5

Amsterdam












2.18.2 The same image with "Wavelet tone-mapping".

  • Leave all settings at their default values
  • Enable the “Local Contrast & Wavelets" tool ("Advanced" mode) and then open the "Wavelet pyramid2" expander
  • Set "Scope" (wavelets) to 80
  • Then use the settings visible on the screenshot
  • Of course the appearance is subjective so feel free to change the settings
  • This version of "Tone mapping" is different from the other algorithms implemented in Rawtherapee (Fattal for "dynamic range compression" and Mantiuk for "Tone mapping" & Log Encoding) and is specific to Rawtherapee Wavelets.
Amsterdam image with wavelet tone mapping











2.19 Three ways of increasing texture

For demonstration purposes we can use

  • Tone-mapping (Mantiuk)
  • Retinex
  • Wavelets

2.19.1 Preparation – original image - Venice

Preparation

Raw file: [10]












2.19.2 Using Tone mapping

  • Note that the option "Normalize luminance" is checked. This ensures that the average and variance of the luminance values are the same as in the original image.
  • Use "Advanced" mode and adjust "Edge stopping" and "Scale".
Tone mapping using the 'Mantiuk' algorithm












2.19.3 Using Retinex

  • Note that the option "Normalize luminance" is checked. This ensures that the average and variance of the luminance values are the same as in the original image.
  • Note also that you can enable the "Use Fast Fourier Transform"
Retinex











2.19.4 Using Wavelets

  • Note the use of "Dynamic range compression", the values of "Attenuation response", "Balance threshold" and "Compress residual image".
  • Try "Contrast by level".
  • Also try "Directional contrast",
  • or a combination of these parameters
Wavelet tone-mapping












2.20 Merging layers using blend modes

You can use "Merge file" in the "Color and light" tool (advanced mode) to simulate the effect of merging layers. Each RT-spot can be thought of as a layer and the "Merge file" function allows you to merge up to 2 RT-spots with the original image.

  • The first "layer" is called "Original" and corresponds (in the same way as an "Excluding spot") to the image data prior to any local adjustments being carried out.
  • When you stack RT-spots on top of each other, for example 6:
    • If the current Spot is number 6, "Merge file" will merge the 6th (layer) , either with the 5th (Previous Spot), or with the "Original Image" (the original data), or with a color defined in "Background" depending on the option chosen in the combobox.
    • If the current spot is number 3 out of the 6, then "Merge file" will merge spot 3 either with the 2nd spot (Previous spot), or with the "Original" (the original data) or with a color defined in "Background".
    • For each of these merges you have 21 blend modes inspired by those of Photoshop (C) (Normal, Difference, ...Soft light, ...Overlay, ...)
    • For each blend mode you can adjust the opacity, deltaE, and a "contrast threshold" (except in the case of "Background" )
    • The Graduated Filter (Luminance, Chrominance, Hue) - located in "Color and Light" - also works with "Merge file".

As an example we will use these features to create a variable blur (of course this isn’t the only application).

2.20.1 Preparation

Add an RT-spot as in previous examples and then add the "Blur/Grain & Denoise" tool in "Advanced" mode to the spot using "Add tool to current spot" .

  • Set the RT-spot to "Inverse" mode (using the checkbox which will appear when you click on the "Blur & Noise" expander).
  • Choose "Scope" = 90 or 100 depending on the desired effect
  • Set "Radius" to a high value (2000 or more and check the FFTW option), set Blur mode to "Luminance & Chrominance".
Préparation

Raw file: [11]











2.20.2 Adding a second RT-spot

Use "Add tool to current spot" to add the "Color and light" tool and set it to "Advanced" mode

  • Set "Scope (color tools) " to 100
Second spot












2.20.3 First merge in "normal" blend mode

  • Go to the "Merge file" expander in the "Color & Light" module.
  • In the combobox choose one of the options in the list that starts with "None". The options are:
    • "Original Image"
    • "Previous Spot" which merges with the previous RT-spot (or the Original Image if there is only 1 RT-spot)
    • "Background" which allows you to merge with a colored background;
  • Then choose the blend mode (under the heading "Merge with Original or Previous or Background" ) and adjust the settings : "Merge background”, "Opacity”, "Contrast Threshold”
  • The other parameters in the "Color and Light" module can also be used if you wish (e.g. "Lightness”, "Contrast”, "Saturation” etc.).
Blend mode "Normal"













2.20.4 Second merge using the Soft Light blend mode

In the list of merge modes try "Soft Light (legacy)" (or another mode...)

  • Try adjusting the settings (e.g. "Opacity", etc.) to see what difference they make.
  • Switch from the "Original Image" option to previous "Previous Spot" and see what difference that makes.
Blend mode "Soft Light (legacy)"












2.21 Using a simple mask to improve color selection

2.21.1 Preparation

  • We are going to use an image of the salt mountain in Pammukale (Turkey).
  • It is a difficult image to process, because of the subtle differences in color between the sky and the mountain. Moreover the mountain contains many irregularities.
  • The preliminary steps are the same as for previous examples. Note the setting of "Scope (color tools)" to 40 which is a compromise but necessary if we are going to process the mountain correctly.
  • For the purposes of this example, we are going to strongly increase the luminance (lightness) and the chrominance of the mountain (this is not an artistic objective) and see if we can avoid affecting the sky in the process.
  • We could have used "Excluding spots" (or in a future GUI release, a polygon), but for now, we are going to use a simple mask. We could also have used several curves for the mask, or created several masks by duplicating the RT-spot.
  • With "Local Adjustments", 2 types of mask can be managed:
    • 1) those that don't add or subtract the mask from the image. The aim in this case is to improve the quality of the deltaE selection.
    • 2) those that make use of the resulting differences when they are added to or subtracted from the image.
    • We are going to use the first case (selection improvement ).
Preparation

Raw file: [12]












2.21.2 Strongly increase "Lightness" and "Chrominance"

  • Observe the result: there is color bleed and the sky has been affected by the changes, which is what we wanted to avoid.
Increasing the lightness and chrominance












2.21.3 Creating a simple mask

  • We are going to use only one of the 3 LCH curves (in this case L)
  • Examine the L(L) curve closely. You will see that the point of inflection is located at the transition between the gray areas. This "transition" corresponds to the 3 references of the RT-spot (chroma, luma, hue) and is common to all the curves -- C(C), L(L), LC(H).
  • Avoid using "blend" to ensure that only the shape detection is improved
  • You can also use "Show modifications with mask" in "Mask and modifications".
Show the mask













2.21.4 Fine tuning the result

  • Set "Mask and modifications" to "Show modified image".
  • Activate "Enable mask"
  • If necessary, adjust the "Smooth radius" mask.
  • Retouch the "Contrast curve" mask and L(L) curves if necessary.
  • Switch to "Advanced" mode and try the "Gamma", "Slope", and "Laplacian threshold " masks (instead of the "Smooth radius" mask)
  • Certainly it is not perfect, but much better...the goal is to discover how the masks work

To improve the mask performance, you have 2 solutions:

  • Duplicate the RT-spot: if you duplicate the RT-spot, and place it alongside the previous one, the slight change in the position of the center (references), will allow the second mask to 'correct' the "anomalies or incompleteness" of the previous mask. Moreover this option allows you to readjust certain parameters if necessary in the second spot (in this case lightness & chrominance) to give a more homogeneous result.
  • Use the mask of another open tool (if of course the tool is equipped with a mask). In this case you keep the same references (luma, chroma, hue) to create the masks and to take into account the deltaE (Scope).

Consideration of deltaE:

  • You can disable the core function of "Local Adjustments" - i.e. the "Scope" function which takes into account deltaE - if you want to work entirely with masks and ignore "Scope". In this case set "Scope=100". Obviously the "Scope" function is disabled, so you will only be able to use the "blend" function to combine the mask and the image.
  • When you use the "Mask Tools" sliders available in "Mask & modifications" (Contrast curve mask, chroma mask, gamma mask, etc.), you must remember that they are sensitive to the specific deltaE settings for the mask i.e. "deltaE image mask " in the "Settings" module.
Result












2.22 Blending a mask with the original image

In this example, we want to increase the impression of perspective (relief) of the Pagodas.

2.22.1 Preparation

  • We could have used specific tools here to give a heightened impression of relief e.g. CBDL (Contrast by Detail Levels) or a Wavelet pyramid
  • But for the purposes of this demonstration, we will use a mask with "blend".
  • The preparation is identical to previous examples with "Scope (color tools)" set to 40 (arbitrary), and "Color and Light" in "Advanced" mode
Preparation

Raw file : [13]












2.22.2 Mask settings – what not to do

  • For the purpose of this demonstration we will use 2 features:
    • the LC(H) curve to select the colors
    • a "Blur Mask" which combines a contrast threshold and a blur function
  • Note the checkbox "FFTW", which although it consumes resources, increases the possibilities and the quality of the results: in the case without FFTW the radius is limited to 100 whereas with FFTW it is increased to 1000.
The mask













2.22.2.1 Results
  • Once again, activate "Enable mask".
  • Set the value of "Blend" to whatever you like
  • Adjust the "Smooth radius" mask if necessary.
  • If you have enabled the non-mask settings of "Color and light" (lightness, contrast, etc.), the "Spot structure" slider will have an effect.
  • You can see that the image now has a dominant color. This is caused by using the "Blend" function with the LC(H) curve.
    • switch the curve to "Linear" mode and you will see that dominant color disappears
    • to overcome this problem avoid combining several mask settings irrespective of whether they use "Blend" or not.
    • if you need to combine these settings, it is advisable, as in the simple mask case above, to create either a second (or several) RT-Spot(s) using the "duplicate", function and setting one to "Blend" and the other without (or with different "Blend" values). You can also use another mask associated with another tool.


2.22.3 The right approach

As seen above, we need to take a two-step approach, for example by creating 2 spots:

  • the first one to take into account the LCH curve
  • the second to act on the structure
2.22.3.1 Working on the structure

There are several mask-type tools (in "Advanced" mode) which allow you to modify the structure:

  • "Blur Mask" which includes a contrast threshold and a blur function
  • "Structure Mask" which acts directly on the structure.
  • For these two tools, the LCH curves must be inactive (no curves), however if you wish, you can associate the L(L) curve with LCH;
  • "Blur Mask" and "Structure Mask" can be associated with each other
  • "Local contrast (by wavelet level)" and "Wavelet level selection", can be associated with the L(L) mask curve and generate a local-contrast effect.

Reminder:

  • Activate "Enable mask".
  • Set "Blend" to whatever value you like
  • Adjust "Smooth radius" mask if necessary
Result












2.23 How to use the Common Color Mask and an example of how to blend 2 RT-spots

This mask does not work exactly like the other Local Adjustment masks. It does not complement a tool, like the mask in "Color and light" for example, but is a tool in its own right. You can use it to change the appearance of an image e.g. contrast, luminance, color, as well as its texture.

  • It consists of the 3 curves C(C), L(L), LC(H), (or in "Advanced" mode, 3 curves plus "Structure Mask" & "Blur Mask") which will generate differences in the color or structure of the image when compared to the original image.
  • These "differences" are similar to the differences generated by the "Lightness", or "Chrominance" functions in "Color and Light".
  • The color differences between the mask image and the original image are taken into account by the deltaE (ΔE) and transition parameters.
  • Of course you can use it also in association with other tools in the same RT-spot
  • The simple example that follows allows you to understand how it works; it fits with the "philosophy" of Local Adjustments in so far as it makes use of ΔE

2.23.1 Preparation

Repeat the preliminary steps outlined in previous examples and add the tool to the RT-spot.

  • "Add tool to current spot...", "Common color mask" - "Standard", and for the purpose of the demonstration, do not open any other tools.
  • To create the mask, we will simplify the exercise as much as possible by using only 2 curves C(C) and L(L) only take into account the references of the RT-spot
  • Note that the 2 sliders "Add/subtract luminance mask " and "Add/subtract chrominance mask" are not set to zero, so that the user is not confused by a lack of response from the system; the two values -10 are arbitrary and low.
Preparation

Raw file:[14]












2.23.2 Luminance Mask

The curve makes a small change to the luminance.

  • Notice the position of the top of the curve on the gray transition. The "Luminance" mask matches the reference value of the RT-spot.
Luminance mask











2.23.3 Chrominance Mask

  • Notice the position of the top of the curve on the gray transition. The "Chrominance" mask matches the reference of the RT-spot.
Chrominance mask












2.23.4 Preview ΔE

From here you can play with the deltaE (ΔE) between "Image + Mask" and "Original Image".

  • Try increasing or decreasing the "Scope" (make sure you use the "Common color mask" slider and not the slider in the "Settings" module above).
  • Try adjusting the parameters in the "Settings" module "Shape detection" : "Threshold ΔE-scope", "ΔE decay", "ab-L balance (ΔE)", "C-H balance (ΔE)"
Preview deltaE - ΔE











2.23.5 Show modifications

Go to "Show modifications with mask".

  • Adjust "Add/subtract luminance mask " and "Add/subtract chrominance mask " (these sliders could also have been called "Opacity")
Show modifications












2.23.6 Result

You can change:

  • "Scope" (the "Common Color Mask" slider which acts on ΔE)
  • Activate the "Smooth radius" mask, which will try to reduce the artifacts due to the the fact that the mask has been generated by 3 curves - C(C), L(L), LC(H).
  • The "Chroma" mask
  • Adjust the "Contrast curve" mask
  • Try "Scope (ΔE image mask)" in "Settings"  : this slider acts on the mask and takes into account the deltaE of the mask compared to the center of the RT-spot. It is different from the "Scope" (the first slider of the "Common Color mask") which acts on the difference between the original image and the mask you have created

Switch to "Advanced" mode

  • Adjust the "Soft Radius" slider which will reduce any artifacts between the original image and the one obtained after "adding" the mask. The default value is 1 even in "Standard" mode and produces a small variation - even without the mask – which can be seen in "Show modifications".
  • Try the "Laplacian threshold" mask, and note the difference compared to the "Smooth radius" mask.
  • Try the "Gamma" and "Slope" masks.
  • Try to change the structure with one of the tools provided: "Structure Mask ", "Blur Mask ", "Local contrast (by wavelet level)" mask.
  • Try the "Graduated Filter Mask".
Result












Now we are going to enhance the "Common Color Mask" image with the "Merge file" tool in "Color and Light".

2.23.7 Adding a new RT-spot "Color and light” - Advanced mode

For demonstration (and not artistic) purposes , we will use 3 of the 21 possible blend modes

  • Add a new RT-spot
  • Add a "Color and Light" tool in "Advanced" mode
  • Set the "Scope (color tools)" correctly (with Preview ΔE)
  • Choose 3 settings to increase the luminance, contrast and chrominance
Adding an RT-spot













2.23.8 Preparing the "merge"

  • Choose "Previous spot". We are now going to merge the new RT-spot (Color and Light) with the previous one (Common Color Mask)
Preparing the merge












2.23.9 First merge using "Normal" blend mode

  • Choose the "Normal" blend mode
  • We arbitrarily choose 3 settings: Merge background = 54.2 (takes into account the deltaE between the 2 layers), Opacity = 54.2 (about 50% for each), Contrast threshold = 12.5 (takes into account the differences between uniform and textured areas).
  • The two identical values of 54.2 are arbitrary and you can choose other values 43, 68, etc.
Merge with ‘Normal’ blend mode













2.23.10 Second merge using "Soft Light (legacy)" blend mode

  • Change the blend mode and choose "Soft Light (legacy)".
Merge using Soft Light (legacy)












2.23.11 Third merge using "Color Burn" blend mode

  • Change the blend mode and choose "Color Burn" (the choice is completely arbitrary).
  • Note the differences in luminance and chrominance
Merge using "Color Burn” blend mode












2.23.12 Additional information

Of course, you can create as many "Common color mask" as you want. Simply duplicate the "mask" and place it close to the previous one with similar settings ...

Some important points about the mask curves : C(C), L(L), LC(H)

  • These curves are used to create the mask
  • When the curve is of the first type as shown below (with the highest point of the curve on the selection - in this case L), the selection is improved
  • When the curve is of the second type below (with the lowest point of the curve on the selection -in this case H), the color (or L, or C) will be reduced
  • When the curve is of third type below (with the lowest point of the curve outside the selection -in this case H), the color (or L, or C) will be reduced
Mask selection











  • For this demonstration we used an image with two dominant colors: magenta (flower) and green (foliage). Images that have more varied color, luminance and chrominance (e.g. sky, sea, mountains, houses, fields, flowers, portraits ...) would require more elaborate masks.
  • We stay with the "philosophy" of Local Adjustments, by only relying on the references of the RT-spot. We could of course have used just the curves outlined above but this would have given a completely different result.
  • Similarly, for the merge we chose the same color range as for the mask. We could have made another choice for the second RT-spot, by positioning it on the foliage but the result of the merge would have been different, with less variation in the flowers.


2.24 Correcting an underexposed portrait and improving grainy skin (Mairi)

The portrait of Mairi gives us the opportunity to use several local-adjustment tools. We are going to:

  • Increase the "Exposure" of the image so that it is less dark.
  • Use "CBDL" to soften the skin and "Clarity" to lighten the face.
  • Make a "Graduated filter" to open up the shadows of the face on the right-hand side of the image.
  • Use 3 "Excluding" spots to "exclude" the eyes and lips from the adjustments
  • Use an LC(H) mask to "exclude" the hair from the softening adjustments (to avoid losing definition).
  • Compare the result 'before' and 'after'.
  • Remark: the settings have been given as an indication and are a matter of individual taste
Preparation

Raw file: [15]














2.24.1 Increasing exposure

  • Exposure + 0.5
  • Note: we could have used an RT-spot to limit the exposure increase to a particular area instead of an overall increase in exposure.
Exposure increase













2.24.2 Using CBDL

  • Create an RT-spot with a large "Spot size" = 47
  • Make a gradual contrast reduction for levels 0 to 4
  • Set "Clarity" to 60
  • Set "Scope" to 40
CBDL













2.24.3 Graduated Filter

  • Create another "Color and Light" RT-spot
  • Graduated filter settings: "Luminance" = -0.6; "Gradient angle" = 71.5
  • You can also play with the chrominance settings (Advanced mode)
Graduated Filter












2.24.4 Excluding the eyes and lips

  • Create 3 "Excluding" RT-spots on the eyes and lips
  • Adjust the "Scope" (excluding) to obtain the desired result
Excluding













2.24.5 Hair exclusion mask

  • Go back to the first RT-spot
  • Go to "Mask and modifications"
  • Select "Show mask"
  • Open the LC(H) curve
  • Identify the color of the skin (the boundary between the light and dark gray areas on the graph)
  • Lower the curve as shown in the graph (or similar)
  • Adjust the "Smooth radius" mask
  • Adjust the "Gamma", "Slope", "Contrast curve" mask if necessary
Mask













2.24.6 Result

  • Set the mask to "Show image with modifications”
  • Check the "Enable mask" checkbox
Result













2.24.7 Before and After Comparison

Before & After














2.24.8 An alternative - replace CBDL with "Wavelet contrast by level".

  • The "Wavelet" module is more powerful than CBDL (Contrast By Detail Levels) and may seem more complex given the number of options.
  • However, it allows you to target the CBDL effect by using the "Attenuation Response" (Damper) and "Offset" sliders. This means that instead of applying the changes linearly to the wavelet decomposition signal, they will be adjusted depending on the value of the signal to avoid amplifying defects such as noise.
  • The wavelet option also has a "Clarity" function.
Wavelet contrast by level and Clarity












2.24.9 Using a mask with wavelets (yes it is possible!)

Wavelet mask