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[OM] Re: E-500 senior picture

Subject: [OM] Re: E-500 senior picture
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Fri, 14 Jul 2006 09:44:54 -0400
Nothing as long as the exposure and color balance are perfect. 
Everything if they're way off.  The subject picture was underexposed 
enough that it's not possible to adjust the exposure to the right level 
without introducing a small amount of posterization into the image.

With only 256 integer brightness levels available in a JPEG if the 
brightness is increase by multiplying by, say, 1.5 then a brightness 
level of 100 becomes 150.  But so does a brightness level of 101 become 
150.  The distinction in original brightness levels between those two 
pixels has been lost.  A certain amount is acceptable but after a point 
it begins to look like a poster painted with not enough colors.  You may 
also lose pixels at the bright or shadow ends where multiplication or 
division of the brightness value simply rounds them off to pure black or 
white.

The 12 bit raw image and later conversion into 16 bits for processing 
give you a lot more leeway in adjusting brightness, contrast, saturation 
and color balance which are all things that affect the brightness levels 
of individual pixels.

Chuck Norcutt

Tim Randles wrote:

> what is wrong with JPEG format?



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