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JPEG quality
I was always told that if you keep importing and exporting the same JPEG image, every time you export, it’s compressed some more so the quality decreases. What I’m doing now is fixing some lens dust spots on a video by importing the video into AE, exporting a JPEG seq, importing the JPEG seq into AE, and using a tracking script that allows the spot to be spot-healed in a PS script. PS exports new healed JPEGS. After one spot is removed, the new healed JPEGs are brought into AE as a new JPEG sequence and the process is repeated for each spot. There is one video that I did this process 11 times – so technically, the JPEGS were re-exported 11 times. But when I import the final clip that was fixed onto a video timeline in my NLE, and compare the original with the healed version, the quality doesn’t seem to have changed at all – besides a few pixels (I check with a difference filter). How is this so? Thanks!
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5 Replies
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Quite a few different “flavors” of JPEG exist. A Google search for “lossless JPEG” provides some reading you may find interesting.
It is true that when JPEG was first introduced (after originally being a classified technology used by the military) it was a lossy compression format.
But if your difference matte shows no difference, well. . . sounds like a lossless/near-lossless version of JPEG.
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Yes, I knew that there is a lossless JPEG but since PS only lets you choose the quality (until 12) I assumed that PS exported the regular lossy JPEG. It would be interesting to research if all of PS JPEG exports are lossless since there is no option of lossy\lossless in PS.
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Use this command File+save the web and then select JPEG format
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Consider using JPG2000 at max quality for lossless image sequences in 8-bit RGB. I prefer 10-bit DPX to minimize RGB-to-YCC artifacts.
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I guess you have used the most flexible process to keep your JPG image quality intact.
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