Bill Pearce wrote:
>> You needn't convert it to any format, simply to 16-bit.
>>
> As I understand jpeg, each time a file is saved, some information is
> discarded.
Strictly speaking, I don't think that's true -- the information lost
when you save an image as a JPEG at quality X is constant.
(now, while in theory this is true, in practise, you'd want to use the
same image editing program each time to avoid rounding errors and
whatnot. Note that you can also make changes to some bits of the image,
and they'll only 'spread the lossyness' to the 8x8 tiles around the
changed area.
Note that this implies you know the image editing program and quality
settings used to create the original image -- if I have some arbitrary
jpeg I find online, I can't do this).
Testing, it seems to be true:
Using the same program:
Open some arbitrary a.jpg.
Save as b.jpg, quality 85.
Close a.jpg, open b.jpg, save as c.jpg, quality 85
Now open b and c in [image editor of choice]. Copy b to clipboard,
paste on top of c, set merge mode to 'subtract'. Resulting image is
totally black -- ie, b and c are identical.
-- dan
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