--- "Schlake (William Colburn)" <[EMAIL PROTECTED]>
wrote:
> The Canon jpeg settings are poorly choosen. A high
> quality jpeg from
> the camera or software corresponds to a 100% JPEG
> group conversion.
> Those settings aren't harmful to the image, but they
> basically turn off
> jpeg compression, so your image is huge with no
> quality gain over a
> lower setting.
Correct me if I am wrong, but JPEG is all about
"Lossy" compression - the lower the compression
quality, the higher the loss of information in the
picture (leading to artifacts, etc.). Now at 100%, the
loss may be minimal but there should still be some
compression - a difference which shoudl be measureable
by saving the same image as a bitmap (RGB - no
compression) and comparing the file sizes. The bitmap
should still be bigger than a 100% quality JPEG.
Another proof of this is that at for all files at 100%
(with the same dimension) the file should be exactly
the same - which is obviously not the case since the
file size will vary depending on the scene complexity
even at 100%.
> A low quality jpeg from the camera
> or software
> corresponds to a 90% JPEG group conversion, which is
> what an ideal high
> quality should be.
At 90% the loss would begin to be barely noticeable
but may present the best tradoff between file size and
quality. For web display use, I usually keep 90% only
if the image is intended to be 800x600 or below. For
archival, I am satisfied with 90-95% at all sizes, but
I guess that is a preferentially variable value.
- Harman
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