I have found that the 65% wedge in the adobe colour swatches pallette, prints on archival matte paper, to a good proximity of a kodak grey card. (We can't get the real thing here so I did a little experimentation to make my own)
If you want a good yardstick for what an 18% grey card looks like in photoshop, with your camera, in your colour-space, on your monitor etc... There's no substitute for setting up a card, shooting it with a custom white balance and a 20-step greyscale in the image area so you can get the exposure right. Open it up in RAW using the camera settings and there ya go!
One of the things that I have learned as a technocrat is that we are making images for human consumption... mostly human eyes, not measuring devices and the closer we steer to that outcome, the more useful our technology and science will be. Otherwise we could go around using complex experimentation to figure out a simple way to do something that nobody wants to do in the first place.
Herschel Mair
Head of the Department of Photography,
Head of the Department of Photography,
Higher College of Technology
Muscat
Sultanate of Oman
Muscat
Sultanate of Oman
Adobe Certified instructor
+ (986) 99899 673
----- Original Message ----
From: ADavidhazy <andpph@xxxxxxx>
To: List for Photo/Imaging Educators - Professionals - Students <photoforum@xxxxxxxxxxxxxxxxxx>
Sent: Friday, April 6, 2007 7:07:56 PM
Subject: 18% gray item
From: ADavidhazy <andpph@xxxxxxx>
To: List for Photo/Imaging Educators - Professionals - Students <photoforum@xxxxxxxxxxxxxxxxxx>
Sent: Friday, April 6, 2007 7:07:56 PM
Subject: 18% gray item
Hi, I am not sure we discussed this on the list sometime in the past so if we
did forgive me. Someone posed the following question to me:
"What is the RGB value for 18% gray (or 18% grey for that matter) in Photoshop?"
This simple question led to three somewhat different answers from three
instructors in the vicinity.
One simply said: 177
Another said:
RGB is linear scale. It all depends on how your camera is set up. If
it is linear from 0-256 - some cameras are set up this way - then its
18% of 256 or 46!
And yet another:
The only thing I have to add is that the sensors are linear (mostly) and
so is the associated RAW data. If you has access to such RAW data, then
Don's calculations are valid.
However, the data the user generally has for use in programs like
Photoshop (is invariably GAMMA CORRECTED for perceptual uniformity
during image editing... The gamma correction used will vary by the type
of color space used (2.2 for sRGB/A-RGB but 1.8 for Profoto RGB).
(Incidentally, the moment a RAW file is opened in PS, it is GAMMA
corrected).
So basically, one has to undo this GAMMA correction before assuming
linear data. After that, you take 18% of whatever your scale is (0-255
for 8 bit, 0-65535 for 16 bit etc)
P.S.: Incidentally, meters don't use 18% gray for calibration...I think
ANSI standards are more like 12%. But then, does anyone use hand-held
meters anymore in this digital world :-)
...... so, what to make of all this? Anyone on the list have something to
contribute???
;)
andy
did forgive me. Someone posed the following question to me:
"What is the RGB value for 18% gray (or 18% grey for that matter) in Photoshop?"
This simple question led to three somewhat different answers from three
instructors in the vicinity.
One simply said: 177
Another said:
RGB is linear scale. It all depends on how your camera is set up. If
it is linear from 0-256 - some cameras are set up this way - then its
18% of 256 or 46!
And yet another:
The only thing I have to add is that the sensors are linear (mostly) and
so is the associated RAW data. If you has access to such RAW data, then
Don's calculations are valid.
However, the data the user generally has for use in programs like
Photoshop (is invariably GAMMA CORRECTED for perceptual uniformity
during image editing... The gamma correction used will vary by the type
of color space used (2.2 for sRGB/A-RGB but 1.8 for Profoto RGB).
(Incidentally, the moment a RAW file is opened in PS, it is GAMMA
corrected).
So basically, one has to undo this GAMMA correction before assuming
linear data. After that, you take 18% of whatever your scale is (0-255
for 8 bit, 0-65535 for 16 bit etc)
P.S.: Incidentally, meters don't use 18% gray for calibration...I think
ANSI standards are more like 12%. But then, does anyone use hand-held
meters anymore in this digital world :-)
...... so, what to make of all this? Anyone on the list have something to
contribute???
;)
andy
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