Thank you for making this comparison. I can see the damage done by JPEG
even in the small thumbnails. Softening of detail, lower contrast, less
color variation. In the enlargements the differences are obvious.
As you state, the result of the subsampling option lowers the amount of
"damage" but it also makes the compression hardly meaningful (about 10%?).
And, the compression we are looking at, at 100% is only 2:1 at best. If
this is the type of "translation" JPEG is causing at that ratio, the 7:1
is going to be pretty damaging.
I am going to do some of my own test. I don't have a web page, but I'll
report on the results, or upload small segments to the group. I suspect
a 7:1 compression is going to look like one (Call it researcher bias) ;-)
> OK, Ed, I'll bite!
> I've just tried to do some sort of meaningful comparison of originals
> versus JPG's at 100% quality, and the results are here - no apologies for a
> hastily knocked up, ugly, web-page ;( :
> Note that 1024 x 768 resolution would be useful for viewing these images.
> (But don't panic, I'm only using tiny bits of a scan, and the total web
> page is only about 40K - I have set it up so that your browser does the
> In summary, I think that although the differences CAN be subtle, if using
> any form of lossy compression, keep your eyes VERY wide open, and your
> magnifier ready!
> If my methodology is suspect, fire away..
> Regards, Mark T.