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Is there any combination of tools in Adobe Photoshop or in any other graphic design software (GIMP, ImageMagick) that would allow me to achieve this kind of image transformation?

  1. The raster layer has opaque areas.
  2. A point is set.
  3. The opaque areas' "exit colors" (or average colors) are then projected outwards from the point, filling the space behind the areas until the end of the canvas is reached.

Simplified, the aim is to make opaque zones drop infinite flat shadows behind them, shadows being of the same color they are projected from. I have attached two images to illustrate the desired transformation:

enter image description here

enter image description here

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  • You can sort if do this with motion blur. Anyway this becomes easier to build if you convert the image to polar coordinates for the transform. Convolove many times. Then inverse polar back.
    – joojaa
    Feb 17 at 21:41
  • Ok i know how you can do this with minimalish effort. But now i got to sleep.
    – joojaa
    Feb 17 at 22:18
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Here is an idea for Photoshop. There are a few steps, so I'll just explain the general procedure without going into every detail. Feel free to ask for clarification.

I'll use this image with some random colored blobs as an example:

The red cross is the wanted center.

First we need to make sure that the wanted center is exactly in the center of the image. A way to do that is to first crop the image to the center pixel with Delete Cropped Pixels ticked off and then afterwards use Image > Canvas Size to expand the canvas again.

The image I'm using is 640 × 480 px, so I expand the canvas to the double of the original (to be sure not to crop anything) plus 1 px (to make sure the cross is exactly in the middle). So I end up with an image that is 1081 × 961 px:

You can of course manually crop it smaller if you want as long as you make sure to keep the cross in the center.

Delete the center cross and use Filter > Distort > Polar Coordinates set to Polar to Rectangular. This assumes that the image is a circular image which you then stretch out to fit a rectangle with the center in the top and the outer circumference in the bottom:

Now we need to make the color blobs continue downwards until they hit the lower boundary of the image. Sadly, as far as I know, Photoshop hasn't got an easy way to use a whole image as a brush. Clone Tool doesn't allow drawing lines and the different blur filters are too destructive. Furthermore, as you want the "exit pixels" to project outwards we need to make sure that we keep painting below the current image.

So for this I record an action:

  • Ctrl + A to Select All.

  • Ctrl + C to Copy the current image to clipboard.

  • Filter > Other > Offset with the following settings to nudge the whole image 1 px down:

  • Shift + Ctrl + V to Paste in Place the previous image.

  • Shift + Ctrl + E to Merge Visible.

This just paints 1 px so I record another action where I repeat the previous action many times and assign that action to a function key. You can also just record one and afterwards copy that event in the Action panel.

Now I can press the function key until the blobs continue to the edge of the image:

(The playback speed has been significantly increased. This is a very slow way to do it. There might be an easier way to achieve this.)

All that remains to be done now is to use Filter > Distort > Polar Coordinates set to Rectangular to Polar and we have a result:

As you might notice, the result is a little blurred from being distorted back and forth. Depending on what you want to use this for, it might look good if you paste in the original image on top to bring the objects back to their original sharpness.

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  • @joojaa, I see your comment now after posting. Perhaps this is the same approach as you mention? Except the action I made here is rather clumsy.
    – Wolff
    Feb 17 at 22:37
  • Yeah. You can nudge copy layers with a builtin shortcut though.
    – joojaa
    Feb 17 at 23:00
  • @joojaa, but the copy needs to be underneath the original because the OP wants the "exit" pixels to project outwards.
    – Wolff
    Feb 17 at 23:01
  • Ah yes good catch.
    – joojaa
    Feb 17 at 23:02
  • By the way the benefit if the action trick is that you can also use it to fade, blur or anything really to the layer below too.
    – joojaa
    Feb 17 at 23:04

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