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RE: [APML] Photoshop conversion to jpeg
Hello
I'd have to ask which version of photoshop you have. If you have 7, you
should use the 'Save for Web' option under File, then select JPG.
Within photoshop 7 this is the most effective way to shave the spare
bits out of your files for presentation on the net or other 'streaming'
platforms (like power point presentations and such) which are intended
to viewed by a human.
However, be aware that JPG, in particular, is a lossy compression
algorithm. This means that you only want to do this ONCE to your file
because each time you do it, you not only lose data, but you change the
colors of your image somewhat. So if you use JPG always keep a copy of
your original file somewhere safe.
If your slideshow or viewing application requires higher resolution then
you might consider TIF as the next choice -- in particular TIF with LZW
compression if the application can handle it. LZW is a friendly
compression that wont damage data and in fact is similar to the popular
ZIP compression format that gets used on files in general.
PNG is another good choice if your application can handle it. Though
quite a few apps have no idea what PNG is and aren't quite there with
support for the new format.
Here is a quick introduction on this very subject from an article I
wrote a while back [ hopefully you find it useful :-) ]:
http://www.renderosity.com/index.ez?viewStory=3491
ALSO, do not convert your color space to CMYK as this will reduce the
number of colors in your image!! You want to stick with RGB or LAB
(L*a*b).
The Photoshop help actually has an excellent explanation of the various
color spaces. Do a search for 'Color gamuts' to get a good, quick
overview.
And, finally, you can check out some of the standar file formats out and
their 'specs' here:
http://www.audre.org/GraphicFAQ/2d-hi.html
(these pages are a bit older but those original specs are still pretty
much the same -- if you want more current specs, I suggest checking out
the related news groups)
Hope that helped!
audre
Attic-World - Web Hosting
www.attic-world.net
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-----Original Message-----
From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org]
On Behalf Of Bert Katzung
Sent: Wednesday, April 28, 2004 1:56 AM
To: Discussion of Film Astrophotography
Subject: Re: [APML] Photoshop conversion to jpeg
Hi Alan:
You need to use the "Save As" option in Photoshop in order to be offered
different formats. Then select the one you want (JPEG in this case) and
type in the name (if it's not there already). Bert
Bert Katzung
katzung1@comcast.net
www.astronomy-images.com
----- Original Message -----
From: "Alan Voetsch" <alanv12952@yahoo.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Tuesday, April 27, 2004 9:03 PM
Subject: Re: [APML] Photoshop conversion to jpeg
> Hey Bert,
>
> I'm pretty much done with them, at least what little I can do to them.
> I spent many hours last week working with levels, curves, etc... after
> re-scanning some older negs. First time scanning since I've had the
> newer computer (March '03), which is the reason I got this computer in
> the first place.
>
> The negs have been in 16 bit mode all the time.
> I wouldn't know about normal looking histograms, some of mine end up
> looking pretty strange. 8-)
>
> The other thing I was wondering about is; after converting to 8 bit,
> will the 'save' dialog box offer me the option of saving as a jpeg?
> Or, will I need to look somewhere else?
>
> For those wondering, these were the very first images I've processed
> in 18 months, hence the elementary questions. And let's face it, I've
> never claimed to be a Jerry Lodriguss anyway! 8-)
>
> Thanks Bert,
> Alan
>
> --- Bert Katzung <katzung1@comcast.net> wrote:
> > Hi Alan:
> > Yes, I believe that jpegs cannot be created from 16 bit files --- at
> > least that's what photoshop tells me when I forget to convert from
> > 16 to 8 bit
> > before asking it to make the jpegs for my web site. However, keeping
> > the 16
> > bits is really most important when you're stretching (especially)
and
> > doing
> > other things in the early stages of processing astro files. Once you
> > have
> > the image worked up to a normal-looking histogram, converting to 8
> > bits
> > won't have any major impact on the apparent quality of the image.
>
>
>
>
>
>
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