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RE: [APML]: Picture Window's Blend




Steve:

Photoshop, too, only does pairwise averaging. Contact Matt Considine on 
this list, whose "ADDPIX" program can add and average any number of .RAW 
files.

Regards,

Ben

-----Original Message-----
From:   Steve Bell [SMTP:sb635@delphi.com]
Sent:   Friday, May 08, 1998 7:17 PM
To:     astro-photo@nightsky.com
Subject:        Re: [APML]: Picture Window's Blend


Ben Gomes-Casseres wrote:
>
> The two methods may not be equivalent. It seems to me that you would be
> loosing some fractional information if you "average" by pushing down the
> curve from 255 to 128 and then adding, as PS will round the fractions to
> integers. With a true average (add and then divide) you shouldn't get 
this
> loss (if PS does the math right...). I encountered this problem when 
adding
> 10 solar eclipse images (i.e. need to push the curve down to 25!). With 
two
> images the loss of information is probably negligible.
>

I see what you mean. So, if possible, it is always better to do a true
average to create the final image, instead of a histogram compression
and then an Add. Of course, you can only work with two images at a time
with these programs (except Mira A/P, I think). At least this is true
with Picture Windows and PhotoPaint. I don't know about Photoshop. I
believe you mentioned Matt Considine wrote a DOS program that can do
many images at once? Is it available? What format(s) (TIF, GIF, etc) can
it handle?

BTW, those are some real nice solar eclipse shots.

--
Clear skies,
Steve Bell
mailto:sb635@delphi.com
Astrophoto page: http://www.mindspring.com/~sb635