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This is obviously a bug, and I have reported it to Adobe people, but it doesn’t appear to be getting any attention, so I thought I’d post it here, because I am curious if I am the only person to have noticed it. The bug has existed at least since Photoshop 7, I haven’t tested earlier versions, and I thought for sure that it would have been fixed in CS, but alas it is still there. I noticed it because I couldn’t get PS to crop and rotate my photos to straighten the horizon.
Basically the crop tool, when used to resize and rotate at the same time dramatically distorts the image if the final image needs to be downsampled (shrunk) to achieve the final size. The mathematical term for the kind of distortion taking place is a shear. The more that the angle of rotation differs from 0, 90, 180 or 270 the more severe the distortion, with 45 degree angles being the worst. However, only a small reduction in pixel dimensions causes a pretty noticeable shear. Basically, the algorithm for choosing the source pixels for resampling the image is very wrong.
If you have never seen this bug in action it is very simple to demonstrate:
1. create an image, and fill it with a big chunky checkerboard pattern.
2. choose the crop tool and set the size (in the option window) to half the size of the file you created.
3. drag out a cropping rectangle, about 3/4 the size of your document
4. rotate it 45 degrees
5. hit enter
If you follow these steps, you should see a rotated (good) and sheared (bad) version of your checkerboard image.
Basically the crop tool, when used to resize and rotate at the same time dramatically distorts the image if the final image needs to be downsampled (shrunk) to achieve the final size. The mathematical term for the kind of distortion taking place is a shear. The more that the angle of rotation differs from 0, 90, 180 or 270 the more severe the distortion, with 45 degree angles being the worst. However, only a small reduction in pixel dimensions causes a pretty noticeable shear. Basically, the algorithm for choosing the source pixels for resampling the image is very wrong.
If you have never seen this bug in action it is very simple to demonstrate:
1. create an image, and fill it with a big chunky checkerboard pattern.
2. choose the crop tool and set the size (in the option window) to half the size of the file you created.
3. drag out a cropping rectangle, about 3/4 the size of your document
4. rotate it 45 degrees
5. hit enter
If you follow these steps, you should see a rotated (good) and sheared (bad) version of your checkerboard image.
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