RASC Hamilton Pentax Astro Tracer

[David Galbraith]

There's compression and then there's compression. "lossless compression" changes file size without altering pixel-by-pixel raster data. Lossy compression (like JPG) alters the bitmap data to save file space. Some cameras can store data straight to TIFF files. No loss.

--- Original Message ---

From: "Mark Kaye" <mark.kaye at sympatico.ca>
Sent: November 30, 2013 8:18 AM
To: astronomers at hamiltonrasc.ca
Subject: Re: RASC Hamilton Pentax Astro Tracer

On 13-11-30 7:51, Andy Blanchard wrote:
> Hi Mark, I was wondering why you think the best way to do dark
> subtraction is to let the camera do it? Is this based on fact or
> conjecture? As I have been telling my students just the opposite.

     Both Terry and Alan have done side by sides using darks and letting
the camera handle it.  They both conclude that the camera does a better job.
    I always assumed that RAW meant you get exactly what the chip
produces.  Turns out this is not the case.  When looking at the data for
the ORFs that came out of the Olympus, I noticed a value indicating the
percentage of compression.  Since I thought that RAWs where not
compressed, I did some research and discovered that even RAW images are
compressed.  It is much less effective to do your dark processing on
compressed images, even the small amount that is done to RAW images.

--
    Clear Skies!
                MK

http://www3.sympatico.ca/mark.kaye/index.htm

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://hamiltonrasc.ca/pipermail/astronomers_hamiltonrasc.ca/attachments/20131130/15809ad7/attachment-0002.htm>
-------------- next part --------------
_______________________________________________
astronomers mailing list
astronomers at hamiltonrasc.ca
http://hamiltonrasc.ca/mailman/listinfo/astronomers_hamiltonrasc.ca