Re: [APML] Layers (8 vs. 16 bit images)

["Dick L." <rlocke1@houston.rr.com>]

Title:

All, I now get the AP digest, which seems to arrive semi-monthly, so I'm usually going to be way behind on anything I contribute.

I followed 8 bits using layers discussion with interest, some of which is below.  I previously went along with the conventional wisdom, that 16 bits was way better than 8 bits.  (And Adobe wouldn't want to discourage this thinking, as it helps facilitate sales of CS.  Hardware vendors are kind of in the same boat.)  

Dan Margulis in "Professional Photoshop" (4th ed.) has considerable discussion of 8 vs. 16 bits.  Based on a good deal of experimenting, he basically concludes that "real world" differences in working with 8 vs 16 bits are negligible.  (I realize that astrophotography is borderline real world, but nonetheless I think he's right.)

So: I wouldn't let the 8-bit conversion in PS7 stop me from working with layers, if layers are called for.  And there's a lot you can do with layers that you can't do otherwise.

What I do now is capture and save in 16 bits from my camera/scanner.  Allow the scanner/camera to do absolutely no image processing.  I then open an image in PS, and adjust curves or levels if there's any kind of gap in the histogram (i.e. if the curve ends before the top or bottom of the scale.)  I then convert to 8 bits and don't look back.

BTW, while this book is not for the faint of heart, it's really taught me a lot.  The powerful techniques of blending one channel into another are covered extensively - and you need to use layers to do it ;-).

-Dick L.

Date: Sun, 14 Nov 2004 18:07:29 +0100 (CET)
From: "Carlos Milovic F." <cmilovic@yahoo.es>
Subject: Re: [APML] Layers
To: Discussion of Film Astrophotography <astro-photo@seds.org>
Message-ID: 20041114170729.57517.qmail@web60204.mail.yahoo.com"><20041114170729.57517.qmail@web60204.mail.yahoo.com>
Content-Type: text/plain; charset="iso-8859-1"

> >Well, this is a big problem then. Why would anybody want to work in
> >Layers? Also, every time I've gone in and used the brush tool (8 bits),
> >and then converted back to 16, I have been screwing things up?
 Yes. Well, try to do as much as you can in 16bits (levels and curves,
mainly), and then go "down" to 8bits.  
> >Is there a work-around? Obviously many folks here are using layers
> >without paying a huge price. Possibly, the only option is CS? I
> >currently use PS7.
 If you are working with 16bits, due the limitations of PS7, just
don't care about using adjustement layers. It will be much better to work
with common adjustements in 16bits, than layers at 8bits.   BTW, as I suggested
to you before, try using PixInsight LE for all the basic adjustements. There
you can perform histograms (levels) and curves adjustements with a 32bits
accuracy. Also, you can apply a lot of noise reduction techniques... http://pleiades-astrophoto.com



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