Re: [APML] PS-LZW compression?

[steve banbury <banburys@sonic.net>]

Hi Alan--I just opened an image file, and saved it in LZW and in no
compression. The uncompressed file size was 1.9 Meg, and the LZW
compressed file was 1.7 meg.  Zoomed the magnification to 400 percent on
both with them tiled side by side in Photoshop--there was absolutely no
difference in the 2 images.

This is what is meant by "lossless". The reduction in file size has no
impact on the image quality. JPEG, GIF and a a couple of newcomers in
the field PNG and MNG all obtain great file reduction with various
degrees of image degradation. I never hear anyone refer to PNG here on
APML, but it is very interesting.

Anyway--saving your file with NO compression, or with LZW makes no
difference in the image quality or subsequent reopening and continued
editing.

Once you open fa file for editing, the "Filters" pull down window at the
top of your Photoshop screen window should be "Active", and let you
fiddle to your hearts content. If "Preview" is checked, you can see the
impact of the filter without actually changing your original. I still
tend to work with copies rather than my originals--because my fingers
are quicker than my brain!  :^{

Steve


Alan Voetsch wrote:

> Bill, Franklin, Jerry, Bert, Steve,
>
> Thank you for your input. Here is what I get out of
> your responses. LZW is OK if I'm not going to do
> anything (post to web) with an image. If I do plan on
> posting to the web at some point (even in the future),
> I should not use ANY kind of compression. Just for
> keeping images on my drive, LZW will save me space.
> Once I apply LZW, is information lost forever?
> Scenario: I'm working on an image. It's night and I'm
> tired, and would like to save the file for tomorrow
> morning. This image may be a keeper as the cover shot
> for S&T. LZW overnight, or not?
>
> Steve and Bert, appreciate the sharpening advice. I
> think I've been hanging out on the SBIG list too long.
> I knoe there are ways to sharpen things up, but I
> think they apply to AIP4WIN, Maxim DL, or DDP
> (whatever Adam Block uses). I can barely do a thing in
> PS, so I've got a ways to go to be able to do what I
> want. I'll try the filters, but if I remember right,
> those options were not active. I'll look again.
>
> Thanks everyone,
> Alan
>
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