jpeg compression

13 years 3 weeks ago #43227 by 0567 gel
Does anyone know of a good resource for explaining jpeg compression, or perhaps anyone have a really good understanding of the subject? Like photoshop have a 1 - 12 scale, 12 being the be the least compression and the highest quality. What I don't understand is if I am editing a jpeg and saving it, how can I know what level to save it at. Say I am editing a jpeg from my Nikon d60 and I want to then save the edited file at the same quality as the edited original, how do I do so? I originally thought that by saving these edited jpegs at the 12 setting (highest quality) it would simply not compress the image any further and it would be the same size and quality as the original. I just want to get the picture from the camera, edit it, and then save it at the same quality as the original. Do I have to test every option and quality level and study the resulting pics and file sizes, or is this info out there already??


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13 years 3 weeks ago #43228 by MylilAngel
I think there are some misconceptions on how jpeg compression works. It has virtually no effect on sharpness and fine detail because it works on the principle of compressing areas of adjacent equal( or similar) tone/colour. It works because areas of similar hue can be defined as a single value of red green and, therefore the information in adjacent pixels can be defined as a single 24 or 32 bit value for the whole area, with an appropriate algorithm to unscramble the position information. There is no point in assigning the same value i.e 24 bits of data to a range of adjacent pixels since this additional data is reduntant and simply wastes disc space.


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13 years 2 weeks ago #44798 by effron

Why so serious?
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