Resize: Difference between revisions

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Resizing can be applied to the cropped area or to the whole image.
[[File:Resize tool 5.4-dev.png|frame|right|Screenshot of the whole Resize tool in RawTherapee 5.4-789-ga7b7f20b8.]]


Choose your preferred resizing algorithm:
== Resize ==
 
Resizing is one of the last things to happen when saving an image - this tool runs after most other tools and transformations. As downscaling an image involves a certain loss of detail, this tool includes a "Post-Resize Sharpening" component which you can use to make the downscaled image crisp.
 
The effects of the Resize tool will not be shown in the preview. The saved image will of course be resized.
 
=== Method ===
 
Resizing can be performed using various algorithms, each with its own strengths and weaknesses. We narrowed the choice down to the two most significant:
* Nearest
* Nearest
: The "nearest neighbor" method of interpolation is meant to be used when you want to resize an image by squares of 2 (2x, 4x, 8x, 16x, etc.) in order to make some pixel-peeping detail larger without introducing smooth blending between pixels. The result will be very sharp, but also very ugly. This is not meant to be used for everyday photography.
* Lanczos
* Lanczos
: Lanczos results in the highest quality sampling and is therefore the recommended and default option.
: Lanczos is the default sharpening method. It is meant to be used for everyday photography and in all cases except for the one described above. It results in a sharp, high quality image. Use it to resize by any amount.


Versions of RawTherapee prior to 4.2.152 also have these additional resizing algorithms, but their use is discouraged as "Lanczos" produces the best results, which is why they were removed in newer versions:
=== Specify, Width and Height ===
* Bilinear
* Bicubic
* Bicubic (Softer)
* Bicubic (Sharper)


You can resize according to:
You can specify what dimensions to scale to or by:
* Scale
* Scale  
: e.g. have the resulting image 0.5 times the size of the full one,
: Use this if you want to resize the image by a specific amount.
: e.g. to make it a quarter of its current size, set scale to 0.25,
: or it make it 4x larger, set scale to 4.
* Width
* Width
: by specifying the desired width so that the height is automatically and proportionally scaled,
: Use this to specify the desired width in pixels, and have the height adapt while keeping proportions.
* Height
* Height
: by specifying the desired height so that the width is automatically and proportionally scaled,
: As for width.
* Bounding Box
* Bounding Box
: by specifying the maximum width and height you want your image to have, and leave it up to RawTherapee to figure out how to proportionally fit your image into this box.
: Use this if you want the image to fit inside a certain width and height.
: e.g. if your image has dimensions 3000x2000 and you want it to fit on a [https://en.wikipedia.org/wiki/1080p 1080p/Full HD] screen, set the bounding box to 1920x1080 and your image will be resized proportionally in such a way that the width will not exceed 1920 and the height will not exceed 1080.


The effects of the ''Resize'' tool will not be shown in the preview. This is a limitation of RawTherapee's current engine. Resizing is done at the end of the processing pipeline. The output image will of course be resized.
=== Applies To ===
 
You will typically want the width and height to apply to the cropped area, however you can also have it apply to the full image, though even then of course only the cropped area gets saved.
 
=== Allow Upscaling ===
 
This setting controls whether the resize tool will also upscale your images, or only downscale. If it is disabled and the combination of image dimensions, crop dimensions and resize dimensions is such that the image would need to be upscaled to meet your target, this setting will prevent it from being upscaled - it will remain at its current size.
 
This setting was introduced in RawTherapee 5.5. If in RawTherapee 5.5 you use a sidecar file from an older version of RawTherapee, this setting will automatically be enabled.


== Post-Resize Sharpening ==
== Post-Resize Sharpening ==
[[File:Rt-4.2.235_postresizesharpening.png|frame|right|Screenshot of the Post-Resize Sharpening tool which is part of the Resize tool available from RawTherapee-4.2.235 onwards.]]
 
Resizing an image often leads to a loss of sharpness, so it is common practice to sharpen the image again after having resized it. With the Post-Resize Sharpening tool you can save crystal-clear images straight away with no further hassle. Because this tool works on the image after it is resized, you cannot use the preview to see what it will do, though this is not a problem because the procedure for finding the right values is straightforward.
Resizing an image often leads to a loss of sharpness, so it is common practice to sharpen the image again after having resized it. With the Post-Resize Sharpening tool you can save crystal-clear images straight away with no further hassle. Because this tool works on the image after it is resized, you cannot use the preview to see what it will do, though this is not a problem because the procedure for finding the right values is straightforward.


The default values work great, but if you want to change them, here's how:
The default values work great, but if you want to change them, here's how to preview what the image will look like:
# Tweak your image as you usually would and enable resizing (e.g. downscale using the Lanczos method to a 900px bounding box),
# Tweak your image as you usually would and enable the Resize tool, e.g. downscale using the Lanczos method to a 900x900px bounding box.
# Save the image to a lossless format such as TIFF,
# Save the image to a lossless format such as TIFF.
# Open that saved TIFF, apply the (Neutral) processing profile if that wasn't done automatically, and enable the Sharpening tool in the Detail tab,
# Open that saved TIFF in RawTherapee, apply the Neutral processing profile if that wasn't done automatically, and enable the [[Sharpening]] tool in the Detail tab.
# Zoom to 100% (1:1) and tweak the Sharpening tool's parameters until you get a result that satisfies you. These are the values you should use in the Post-Resize Sharpening tool.
# Zoom to 100% (1:1) and tweak the Sharpening tool's parameters until you get a result that satisfies you. These are the values you should use in the Post-Resize Sharpening tool.
# Go back to the raw image, enable the Post-Resize Sharpening tool and set it up with the values from the previous step.
# Go back to the raw image, enable the Post-Resize Sharpening tool and set it up with the values from the previous step.


In most cases the default values in the Post-Resize Sharpening tool work great, so give them a try before fiddling.
The Post-Resize Sharpening tool is only available when you use the "Lanczos" resizing method.


For technical reasons, the Post-Resize Sharpening tool is only available when you use the "Lanczos" resizing method.
As the Post-Resize Sharpening tool works identically to the standard Sharpening tool (except that it takes place right at the end of processing), refer to the [[Sharpening]] article to learn more about how the sharpening tools work.

Revision as of 19:37, 2 September 2018

Screenshot of the whole Resize tool in RawTherapee 5.4-789-ga7b7f20b8.

Resize

Resizing is one of the last things to happen when saving an image - this tool runs after most other tools and transformations. As downscaling an image involves a certain loss of detail, this tool includes a "Post-Resize Sharpening" component which you can use to make the downscaled image crisp.

The effects of the Resize tool will not be shown in the preview. The saved image will of course be resized.

Method

Resizing can be performed using various algorithms, each with its own strengths and weaknesses. We narrowed the choice down to the two most significant:

  • Nearest
The "nearest neighbor" method of interpolation is meant to be used when you want to resize an image by squares of 2 (2x, 4x, 8x, 16x, etc.) in order to make some pixel-peeping detail larger without introducing smooth blending between pixels. The result will be very sharp, but also very ugly. This is not meant to be used for everyday photography.
  • Lanczos
Lanczos is the default sharpening method. It is meant to be used for everyday photography and in all cases except for the one described above. It results in a sharp, high quality image. Use it to resize by any amount.

Specify, Width and Height

You can specify what dimensions to scale to or by:

  • Scale
Use this if you want to resize the image by a specific amount.
e.g. to make it a quarter of its current size, set scale to 0.25,
or it make it 4x larger, set scale to 4.
  • Width
Use this to specify the desired width in pixels, and have the height adapt while keeping proportions.
  • Height
As for width.
  • Bounding Box
Use this if you want the image to fit inside a certain width and height.
e.g. if your image has dimensions 3000x2000 and you want it to fit on a 1080p/Full HD screen, set the bounding box to 1920x1080 and your image will be resized proportionally in such a way that the width will not exceed 1920 and the height will not exceed 1080.

Applies To

You will typically want the width and height to apply to the cropped area, however you can also have it apply to the full image, though even then of course only the cropped area gets saved.

Allow Upscaling

This setting controls whether the resize tool will also upscale your images, or only downscale. If it is disabled and the combination of image dimensions, crop dimensions and resize dimensions is such that the image would need to be upscaled to meet your target, this setting will prevent it from being upscaled - it will remain at its current size.

This setting was introduced in RawTherapee 5.5. If in RawTherapee 5.5 you use a sidecar file from an older version of RawTherapee, this setting will automatically be enabled.

Post-Resize Sharpening

Resizing an image often leads to a loss of sharpness, so it is common practice to sharpen the image again after having resized it. With the Post-Resize Sharpening tool you can save crystal-clear images straight away with no further hassle. Because this tool works on the image after it is resized, you cannot use the preview to see what it will do, though this is not a problem because the procedure for finding the right values is straightforward.

The default values work great, but if you want to change them, here's how to preview what the image will look like:

  1. Tweak your image as you usually would and enable the Resize tool, e.g. downscale using the Lanczos method to a 900x900px bounding box.
  2. Save the image to a lossless format such as TIFF.
  3. Open that saved TIFF in RawTherapee, apply the Neutral processing profile if that wasn't done automatically, and enable the Sharpening tool in the Detail tab.
  4. Zoom to 100% (1:1) and tweak the Sharpening tool's parameters until you get a result that satisfies you. These are the values you should use in the Post-Resize Sharpening tool.
  5. Go back to the raw image, enable the Post-Resize Sharpening tool and set it up with the values from the previous step.

The Post-Resize Sharpening tool is only available when you use the "Lanczos" resizing method.

As the Post-Resize Sharpening tool works identically to the standard Sharpening tool (except that it takes place right at the end of processing), refer to the Sharpening article to learn more about how the sharpening tools work.