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Like in this question, I want transform/rotate an image to match another one (by scale/rotation). Specifically, I want to edit a remake of an old image by cropping/transforming/rotating to match the original)

The tool is not important for me but I'm working on a Linux machine, so Gimp seems to be the first choice. I tried the two-layer approach from the answer in the linked question but this doesn't work because while aligning the transparent layer it becomes opaque.

Is there a way (with whatever tool) to select corresponding points in both images and use points to transform one of the images to match?

How would you do this?

  • What kind of contents do the images contain? If they are astro images, then any astro registration tool will do, such as RegiStar. If your images contain something else, then you may need to use a difference layer blending mode to manually align. There may be automated tools out there that can automatically align images, however I am only aware of one for astrophotography. – jrista Jan 24 '16 at 17:34
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    Did you investigate the Hugin suggestion from that other question? There's friendlier info about using the included align_image_stack script here. – junkyardsparkle Jan 24 '16 at 21:27
  • Are the images taken from the exact same place? Or, at least very close to it? You can't change perspective without 3D information. – mattdm Jan 24 '16 at 22:27
  • The pictures are roughly same place and perspective. I made remakes of historical pictures (which had been made with historical cameras) and I just want crop/scale the new pictures to approximately match the old ones. I don't need to match them on a pixel-basis. – frans Jan 25 '16 at 13:10
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    In that case, I would probably just use the scale/rotate tools in gimp. If you want to see the background layer while you do this, make the layer you're working on "hidden" in the layer stack, and adjust the opacity of the tool preview in the tool preferences. – junkyardsparkle Jan 25 '16 at 20:40
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If the two images are only similar, but not taken from exactly the same place, you might want to just stick with a similar cropping, as any control-point based transform might distort your image in strange ways. If you need to adjust rotation relative to the original image, you can load it as a background image in gimp (up or downscaling to your new image as appropriate) for use as a guide.

In order to see the layer while using the rotate or other transform tools, hide the upper layer in the layers stack and adjust the opacity of the preview in the Tool Options tab of the toolbox. Note that some versions of gimp on older hardware might be somewhat unresponsive when trying to rotate large images with the preview enabled, unfortunately.

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