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I'm interested in the computing time needed to display the file when it is already stored locally. And I'm specially interested in mobile devices like phones. The idea is to save some disk space whit run all the pictures trough "jpegtran -optimize" or "jpegtran -optimize -progressive". Maybe some one has a benchmark?

Den
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The time difference is really up to the author of the JPEG decoder. There shouldn't be much difference in decode time if the program decodes the image completely before displaying it. Some decoders will display the image after each scan is decoded and that will obviously take longer. A progressive JPEG has basically the same amount of entropy coded data as a normal JPEG. Each scan of the image layers on more and more detail into each MCU block. The DCT and color conversion steps take the most time, so if the image is only displayed when it's finished decoding, the total time should be similar.

BitBank
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  • Thanks for the info! But my experience now is, it is slower. How ever, not on the phone, but I think there is some caching involved... – Den Sep 20 '12 at 02:42