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JPEG (JPG) Quality


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Dear All,

I'm sorry if this question has been asked and answered elsewhere, but I couldn't find it in a search of JPG/JPEG and quality.

If I save a PDN as a JPG using 100% quality is this still a lossy format? Does 100% quality mean it retains all detail and therefore is not lossy despite the technical definitions of JPG?

(Feature suggestion - and I think this has already been said which is why I'm not posting separately: Context help / explanation box with the quality slider for each image format.)

P.S.: Don't worry about telling me about PNG and all the other wonderful image formats - I'm only interested in whether 100% JPG is lossy!

Cheers,

Alan

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Ash,

Thanks for that. I guess I hadn't really thought of looking outside of Paint's help / forum - was looking for an answer relating to the slider in Paint.Net

Anyway, since I keep finding links to outside sites that would answer my question except the site's dead, Ash's link provides the info below:

Question: Most image software that allows you to "save as JPEG" will ask what "JPEG Quality" you want to use. Usually this is a number between 0.00 and 1.00 or 0 and 100. Does choosing the maximum value for this parameter (1.00 or 100) mean the resulting compression will be lossless?

Answer: NO This is simply a guideline to the software as to how much loss is acceptable. At a maximum, the results will be quite close to lossless, certainly as far as the human eye can detect. At maximum compression the results will almost certainly be unusable. To compress losslessly, the original JPEG specification uses a different method which very little software supports. There are alternative compression techniquess which offer better true lossless compression such as PNG, JPEG-LS, and JPEG 2000. Each has various advantages and disadvantages and all perform similarly. In general anyone that can achieve better than about 2:1 compression for genuine lossless performance is doing very well indeed!

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