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Revision as of 22:07, 2 December 2015 by Ingo (talk) (Post-Resize Sharpening)
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Resizing can be applied to the cropped area or to the whole image.

Choose your preferred resizing algorithm:

  • Nearest
  • Lanczos
Lanczos results in the highest quality sampling and is therefore the recommended and default option.

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:

  • Bilinear
  • Bicubic
  • Bicubic (Softer)
  • Bicubic (Sharper)

You can resize according to:

  • Scale
e.g. have the resulting image 0.5 times the size of the full one,
  • Width
by specifying the desired width so that the height is automatically and proportionally scaled,
  • Height
by specifying the desired height so that the width is automatically and proportionally scaled,
  • 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.

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.

Post-Resize Sharpening

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.

The default values work great, but if you want to change them, here's how:

  1. Tweak your image as you usually would and enable resizing (e.g. downscale using the Lanczos method to a 900px bounding box),
  2. Save the image to a lossless format such as TIFF,
  3. Open that saved TIFF, 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.

In most cases the default values in the Post-Resize Sharpening tool work great, so give them a try before fiddling.

For technical reasons, the Post-Resize Sharpening tool is only available when you use the "Lanczos" resizing method.