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Old May 1, 2005, 10:06 AM   #11
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NHL wrote:
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-> They may 'look' the same overall but you are loosing either the highlight or detail in the shadow, unless the 'digital' image is properly exposed first...
OK, levels might have been a poor example. What about using RAW and then adjusting exposure compensation in the RAW converter? It seems to me that should yield the same result as using exposure compensation to bracket on the camera. No?


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Old May 2, 2005, 2:21 AM   #12
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No - RAW won't help much. Consider the CCD or CMOS pixel a bucket - and light the water that fills it up. If it overflows, you've lost all that extra water - for ever (white pixels). Overexposure is very bad in digital.

If you only get a drop or two of water, you may not be able to see them (black pixels). What RAW allows here is a minor tweak of the interpretation of those few drops - not the number of them. So what you can do is manipulate the curve of light to dark to make the best use of the info you do have. But you don't really need RAW to do that. A high res JPEG with the least compression works just as well.

Again, RAW doesn't alter the info that was captured. It only lets you play with it in more ways. In general, RAW isn't useful for 95% of the population using digital cameras and is actually detrimental to the user that does so casually.






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Old May 2, 2005, 7:32 AM   #13
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I think what bigboyhf is trying to convey (now that he clarified it) is in RAW, the compensation parameters are just passed along in the metadata fields - just like the White Balance, and is then computed (or adjusted) on the PC instead of internal to the camera.

Of course all this will only work if the picture is well center at the mid-point or properly exposed - otherwise who needs shutter speed or aperture control anymore... :G :lol: :-)
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Old May 2, 2005, 7:54 AM   #14
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TDM_Canon_User wrote:
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If you only get a drop or two of water, you may not be able to see them (black pixels). What RAW allows here is a minor tweak of the interpretation of those few drops - not the number of them. So what you can do is manipulate the curve of light to dark to make the best use of the info you do have. But you don't really need RAW to do that. A high res JPEG with the least compression works just as well.

Again, RAW doesn't alter the info that was captured. It only lets you play with it in more ways. In general, RAW isn't useful for 95% of the population using digital cameras and is actually detrimental to the user that does so casually.
Actually this is untrue. RAW files offer more levels and detail than JPG offers. This is because RAW captures data in 12-bit files, where as JPG captures data in 8-bit files. As soon as you go from 12 to 8 bit you lose a lot of data and levels. Here is a simple chart that shows the amount of data available in RAW and JPG Files




[align=center]A 12 Bit raw File
Within the first F/Stop, which contains the Brightest Tones - 2048 levels available
Within the second F/Stop, which contains Bright Tones - 1024 levels available
Within the third F/Stop, which contains the Mid-Tones - 512 levels available
Within the fourth F/Stop, which contains Dark Tones - 256 levels available
Within the fifth F/Stop, which contains the Darkest Tones - 128 levels available[/align]



[align=center]
An 8 Bit JPG File

Within the first F/Stop, which contains the Brightest Tones - 69 levels available
Within the second F/Stop, which contains Bright Tones - 50 levels available
Within the third F/Stop, which contains the Mid-Tones - 37 levels available
Within the fourth F/Stop, which contains Dark Tones - 27 levels available
Within the fifth F/Stop, which contains the Darkest Tones - 20 levels available

Data from http://www.luminous-landscape.com[/align]
Just looking at the first f/stop you can see the amount of data that you can pull out of the picture. So what may look like a blown highlight in a JPG file, might be recoverable in RAW format.

-Travis-
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Old May 2, 2005, 9:03 AM   #15
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I definitely agree with blown highlights being a problem. But given a pic that has a halfway decent histogram should be able to be tuned up in post processing with a slight edge given to RAW files. I think that might be why the meter tends to underexpose as this is more correctable than overexpose...

I have to pick up a set of gray cards though and see the difference for myself! I will be shooting snow and ice on a trip this summer and would like to expose correctly. From whay I understand, even a gray card will be off with very light or very dark subjects. I certainly don't want to blow the highlights on snow and would rather err to slight underexposure.
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Old May 2, 2005, 11:55 AM   #16
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FYI -

http://www.luminous-landscape.com/co...exposure.shtml
http://www.naturespic.com/articles/a.../article4.html
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