P3D RE: JPG and destruction

[Dylan The Hippy Wabbit <spacey@xxxxxxxxxxxxx>]

Hi again,

John Roberts answered Ole Hansen saying:-

>>> JPEG retains the spatial resolution of the original image....
>>It certainly does not !

>I agree. Whatever the process is called, some spatial information is lost
>in the process of lossy JPG compression.

What it does is transform the Red-Breen-Blue description of the colours
into a Grey-Red-Blue one.  The green is implied by the difference between
the greyscale and the combined red-blue values.  Then, based on good
psychological principles, the greyscale retains its full resolution but
the colour components are reduced by half.  The bugger factor for us
stereo nuts is that most software does this horizontally.

Yes, this will be more obvious in stereo than in mono.

Yes, Ole's anaglyphs will be even more badly damaged since he is relying
on the colour resolution to seperate left and right.

No, using the minimum compression/maximum quality setting will make no
difference.  That affects a later stage of the compression.

If you shop around you may find a jpeg program or library which will allow
you to force this subsampling to be done vertically instead of
horizontally.  That would damage interlaced images, but I'd argue that the
interlacing is better done at the display stage rather than storage.

Perhaps Larry Berlin could tell us what Stereo Image Factory does in this
respect?

BTW, I've cross-posted to sd-3d since I believe we'll be asked to move
across if we go into any more detail.

Dave Spacey

______________________________________________________________________________

Walk tall, walk straight,
Spit the world right in the eye.

-Kevin Godley and Lol Creme


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