RE: Film vs. digicam gamma curve
RE: Film vs. digicam gamma curve
- Subject: RE: Film vs. digicam gamma curve
- From: "michael shaffer" <email@hidden>
- Date: Mon, 19 Jan 2004 09:44:28 -0330
Jarkko writes ...
>
A colleague of mine is teaching professional photographers and is
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confused with how digital cameras treat image data. The issue rises when
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trying to compare the gamma curves of film material with digital camera
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performance.
>
>
Here is an example: Let's take a photograph of a target, in which there
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is full black (D2,1), 18% gray (D0,7) and white (D0,0), using a
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professional digicam. When the image is opened in Photoshop, the
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RGB-values in info for black is about 30, gray 127 and white about 240.
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What we would expect for the values would be black 2-4, white about 250
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and gray 46-47 (to represent the photographers gray card, which the
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target is). However the gray looks right on the monitor and further,
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also when printed: it is the gray we started with (D0,7).
Below are my spreadsheet's R=G=B pixel values given 18% reflectance for
gammas 1, 1.8, 2.2 and 2.5. Note that your value assume gamma=1, which
should be the case. I suspect the camera's conversion to RGB space assumes
gamma=2.2 ... altho it would seem closer to 2.5.
gamma = 1.0 1.8 2.2 2.5
W/B
.18 46 98 117 128
cheerios ... shAf :o)
Avalon Peninsula, Newfoundland
www.micro-investigations.com
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