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 11:03:25 -0330
Jarkko writes ...
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then, the printing process applies a some kind of an inverse gamma?
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I should correct my previous post. Regarding your assumed value of '46',
I should have said "... your value assumes gamma=1, which should ^not^ be
the case." ... leastwise, hardly ever and only under special circumstances.
Regarding your response ... I didn't know we were speaking of a "printing
process". You should also clarify "how" you opened these into PS ... e.g.,
without conversion, or by converting from a camera profile to your working
space.
cheerios :o)
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>>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.
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>>
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>>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).
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> Michael writes ...
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> Below are my spreadsheet's R=G=B pixel values given 18%
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reflectance for
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> gammas 1, 1.8, 2.2 and 2.5. Note that your value assume gamma=1, which
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> should be the case. I suspect the camera's conversion to RGB
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space assumes
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> gamma=2.2 ... altho it would seem closer to 2.5.
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>
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> gamma = 1.0 1.8 2.2 2.5
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> W/B
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> .18 46 98 117 128
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> cheerios ... shAf :o)
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> Avalon Peninsula, Newfoundland
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> www.micro-investigations.com
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--
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PixelCom
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Jarkko Viljanen
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Kuuliantie 5
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37470 Vesilahti
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Finland
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tel. +358-3-3 738 738
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gsm +358-400-796 768
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http://www.pixelcom.fi
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