PSP is substantially more powerful than GIMP.
Making these bald statements isn't very helpful. Could you explain
why you think this is so ?
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StephenG
GIMP does not support adjustment layers.
Photoshop was the first program to offer adjustment layers, and PSP followed not too long after. GIMP has not implemented them yet. Until it does it will be second rate.
Yes, you can do some things with layers in GIMP that kind of sort of do some limited adjustments, but it's not the same.
Here's how an adjustment layer works:
You add an adjustment layer the same as you add a regular layer. There are dozens of different types of adjustment layers. One is levels; another is curves. Then you can make adjustments like levels and curves to the image. The adjustment layer is a mask, so you can use any selection tools and paint on it (even with the pressure sensitive airbrush). The adjustments are applied through the mask. In this way if you want to limit the effect to just the shadow area, you just paint a black mask over the rest (perhaps selecting it with the magic wand). If you want to change the amount of the adjustment, you can do so at any time, or even delete it. You can change the order of the adjustments too, and toggle them on and off. You could have several different levels adjustments and switch between them. You could have an adjustment layer to de-saturate the image, or to change the white balance. They're saved with the file, so 5 years from now you can come back and change the adjustments -- or turn them all off and see the original, unedited file.
Another area of PS that is worth the entry price for me (more particularly -- for my employer) is scripting. The scripting language in Photoshop is as easy to use as it is powerful. I realize most people don't need scripting, but if you do, it's great. You just do the action once and PS records it. You can then play it back on an individual image, a folder, or a directory tree. I shoot in high resolution, but one of our apps can only use 1600x1200 images. So I have an action that re-sizes them. Then another that crops them all to a 4:7 aspect ratio. I have actions that do all sorts of things that I do repetitively -- like open every pdf in a folder and convert it to a jpg. I understand you can program GIMP too, but based on the documentation, it's not nearly so easy.