[filmscanners] Re: JPG sharpening [was: Color spaces for different purposes]

["Anthony Atkielski" <anthony@atkielski.com>]

Laurie writes:

> I agree with this; but in many if not most
> cases, the compression level used or required
> is greater then the lowest possible amount,
> ranging from level 6 to level 3 in order to
> get the file small enough to be an email attachment
> or a web site download.

I was thinking only of archived photos.  For Web and e-mail use, in most
cases you can crank the compression all the way up in Photoshop (that is,
set it down to 1, the highest compression setting) and the image will still
look fine.  Unlike some editing programs, Photoshop won't let you compress
the image so much that it really looks bad on the screen; even the worst
setting is still pretty good.

> This statement I do not understand; please
> elaborate.

Most scans, at full resolution, do not actually hold enough detail to make
full use of that resolution, so compressing them into JPEGs really doesn't
sacrifice anything.

Additionally, with the lowest compression settings of Photoshop (level 10),
I have yet to be able to distinguish between the original and the JPEG in
terms of image detail, even when greatly magnifying the image.  Photoshop is
very conservative.

> Surely, this cannot be the case if we are talking
> about raw data as opposed to encoded compressed
> data even at the lowest setting in which there
> still is some compression of the raw data.

There is always some loss in a mathematical sense and a strict sense, but in
practice you won't be able to see the loss when storing full-resolution
scans as JPEGs with the quality setting set as high as it will go.

I've never had any problem losing detail in archived JPEGs as long as I use
the highest quality setting.  I sure would like to see a 16-bit version of
the JPEG standard, though.



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