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I am trying Darktable for raw processing, and I want to crop an image to an exact size (e.g., 1280x720), specifying the content to retain by moving the rectangle around after it's sized. This is pretty standard in most programs I've used (the X,Y+X+Y is usually listed with regular number inputs), but the only thing I can find in Darktable is an aspect ratio, which will helpfully lock the selection to 16:9 but not let me select a specific size.

Is there any way to input an exact size for a crop in Darktable?

  • To clarify: are you asking for something less fiddly than dragging the rectangle to resize it with the problems that the background might not have enough contrast to read the size and that you need to zoom in a lot to have fine enough control? Or are you asking how to ensure that the exported JPEG is the size shown in the crop rather than sometimes being one pixel smaller? – Peter Taylor Dec 17 '18 at 11:37
  • @PeterTaylor The latter is primary, the former also a concern, especially since GTK3 has more display bugs than an entomology lab. – chrylis -on strike- Dec 18 '18 at 0:48
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Yes, you can crop to exact size in Darktable!

Using Crop & Rotate tool, which I guess you were already using, change aspect setting from 16:9 to freehand.

enter image description here

After you have done that you can change the aspect that you want (or size) by dragging the selection bar, which appears when mouse over the edge of picture.

enter image description here

I'm aware that it is a bit fiddly to change crop to a right size, but it should be possible to do.

enter image description here

Hope this helps!

  • It's not a great option, but it does look like it will work. – chrylis -on strike- Dec 18 '18 at 0:49
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You should use combination of crop and export.

First you should define the exact crop ratio (Crop & Rotate tool). Resize and move (the crop) to the desired view.

Then select File on Disk as the Target Storage or click the folder icon to choose where to save the image. In file output size write one of the dimensions of desired size and click Export.

For more details you can check this document.

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    Cropping only to a geometrically congruent region and then resizing means that the image will usually be rescaled. My goal was to avoid rescaling if I could capture an exact region. – chrylis -on strike- Dec 17 '18 at 9:15
  • @chrylis, I am afraid you should use different tools for such task. – Romeo Ninov Dec 17 '18 at 9:21

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