JPEG @ 100% quality

[nickdu]

From the research I've done it seems jpeg 2000 was introduced such that there would be some flavor of jpeg which would use lossless compression. Not sure if I have that correct or not. At any rate, BBPro can convert to jpeg 2000 and as you might expect you don't get the quality edit box. When you convert to jpeg you do get the quality edit box. What's the difference between jpeg 2000 and jpeg @ 100% quality? I noticed that my 30D images at 95% quality go down to somewhere around 2 MB. At 100% they compress to somewhere around 8MB. Just wondering what's happening.

Thanks,
Nick

[DavidB]

I too would like to know the meaning of the JPEG quality percentages; these are widely used in editing applications, but I do not know whether there is a standard 'scale'. What I do know is that I have never detected a compression artefact in a first- or second- generation JPEG at 85% quality or better.

Lossy compression is about trading an (arguably) invisible loss of data for a very significant reduction in file size. But if the compression is overdone or the image is edited and re-saved through several generations, the effects of compression will become very visible indeed. With a sensible workflow, this need not be a problem. But it does create a very strong case for keeping archive copies of original images, whatever format they were originally produced in.

[Chris Breeze]

JPEG 2000 supports both lossy and lossless compression. If you set the quality to 100 it uses lossless compression. At lower settings JPEG 2000 uses lossy compression but typically gives much better quality than JPEGs of similar file size.
Ordinary JPEGs always use lossy compression. At the higher quality settings (e.g. 85 and above) there is little loss in quality. If you set the quality to 95 or above BBPro stores twice as much color information for improved quality but the file size does increase considerably.