rotating and croping causing jagged banding
Rotating and croping an image leads to an odd banding pattern appearing through the image. This does not occur when clipping using a clipping mask or when only cropped or only rotated.
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Richard, at the moment — I believe there is now way to force Illustrator to use the other interpolation method for cropping embedded images.
But you can do this in Photoshop, using these exact controls you show in your screenshot. The problem with this particular TIFF is that it uses the Indexed Color mode, and thus can’t really interpolate patches. If you go to Image > Mode > Grayscale (or RGB), using Bilinear will give you smooth enough rotation, without lying much about original spots.
An image with non-indexed palette still won’t work properly with Crop in Ai, but yes, making the rotation in Photoshop before cropping is a workaround.
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Richard Little commented
How do it force it to do bilinear interpolation? I have tried free transforming the image in photoshop (picture 1) and with bilinear set in preferences (picture 2) but the images are still becoming jagged.
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Bilinear is surely fine. In fact, I use it more often than others for my own purposes in Photoshop.
I wonder what is being used now...And yeah, I think the native Crop is just not the best tool for the task at the moment :(
Anyway, you just can’t crop a rotated image to an orthogonal frame without any recalculation made.
Rasterino’s Crop Image tool does not recalculate, but I wish it was able to crop to clipping mask automatically. -
Hi Egor, sorry for the delay. Is it possible to use bilinear interpolation? These images are for scientific diagrams and my understanding of bicubic is that it can add data not present in the original image. This would not be suitable for publishing in scientific journals.
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Thanks, Richards, I can see what the problem is now and can confirm it. Illustrator allows to crop rotated images with the orthogonal frame, and uses the most crude interpolation method out there to calculate final pixels. It gets even more obvious if you rotate the image further.
Definitely needs to be revised! Thanks for reporting it.
Which solution would you prefer in this case?
1. To use a different interpolation method, like Bicubic (or other method Photoshop offers)
2. To use the rotated frame instead (something like the commercial Rasterino plugins does)
3. Another one — please specify then -
See attached illustrator file
