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<div class="PlainText">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.<br>
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--- Original Message ---<br>
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From: "Mark Kaye" <mark.kaye@sympatico.ca><br>
Sent: November 30, 2013 8:18 AM<br>
To: astronomers@hamiltonrasc.ca<br>
Subject: Re: RASC Hamilton Pentax Astro Tracer<br>
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<div style="background-color:#ffffff">On 13-11-30 7:51, Andy Blanchard wrote:
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<div>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.
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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.<br>
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.<br>
<pre class="x_moz-signature" cols="72">--
Clear Skies!
MK
<a class="x_moz-txt-link-freetext" href="http://www3.sympatico.ca/mark.kaye/index.htm">http://www3.sympatico.ca/mark.kaye/index.htm</a></pre>
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