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Luminous Landscape Forum > Raw & Post Processing, Printing > Digital Image Processing
button
I'm using pro photo RGB as my working space, and as I learned from the "from camera to print" tutorial, pro photo is a 1.8 gamma space. So, I currently have my monitor calibrated to gamma 1.8 with a cd/m value of somewhere around 60, at 5900K (the value of my room lights). However, most of what I've read recommends that a monitor should be calibrated to 6500K, 2.2 gamma. The problem I'm having with my current setup is that when I use camera raw to correct the exposure value of an image (up the exposure to the point of highlight clipping), my highlights look very harsh and seem "crushed" - everything from around 245 or so and above looks like it goes to pure white. Could anyone offer some insight as to what is going on here? I'm using an Eizo ColorEdge CG241W with a spyder 2 calibrator.

Thanks,
John
papa v2.0
try turing off your room lights first.
Schewe
Your Photoshop working space and yous display space have NOTHING to do with each other...if you have a CRT, the cd/m2 should be in the 80-90 cd/m2. If an LCDE more like 140cd/m2. But, in either case, a D-65 and gamma 2.2 will probaby be a better viewing environment. In the case of LCDs, you prolly want to merely profile your display, not try to adjust white point and gamma. If you have a high-end 10 bit DAC and a direct digital connection to the display then you could get away with making adjustments in the display settings but if you don't have a high-end (like NEC using SpectraView puck/software to control the display) then trying to force adjust white balance and gamma will lead to banding.
button
Thanks, Jeff.

If my understanding is correct, the monitor color space simply IS- in other words, it will display a range of color and luminance based on how it's built (although gamma and temperature values are user defined). I also understand that photoshop's working space is user defined, and that in order to preserve as much detail as the program can currently extract from a RAW image, it's best to edit in 16 bit mode with the largest color space possible (pro photo at the moment?). Only when the editting is done and the image is ready for output should you assign a more limited color space and bit depth (8 bit sRGB for jpeg for web output or the appropriate ICC profile for print).

What I dont understand is if (and if so, why) the gamma of the chosen working space matters. The gamma of pro photo was mentioned in passing on the video, and made me wonder about its effect, if any, on how the monitor handles luminance.

Thanks,
John
digitaldog
QUOTE (button @ Nov 19 2007, 02:34 PM)
What I dont understand is if (and if so, why) the gamma of the chosen working space matters.  The gamma of pro photo was mentioned in passing on the video, and made me wonder about its effect, if any, on the monitor handles luminance.
*


That defines how edits are applied to the data.

http://www.adobe.com/digitalimag/pdfs/phscs2ip_colspace.pdf:

QUOTE
There are two primary attributes of these synthetic RGB working spaces to consider. Clearly the most important is the gamut of the color space. As discussed, the scale of the RGB primaries can differ within the gamut of human vision. The gamut of these RGB working spaces ranges from small to very large. As you will see, the size of the working space gamut can play a profound role in how you edit and eventually output your images.

The other attribute is called the gamma encoding of the working space. This gamma encoding has no relationship to the gamma of your display! Rather, this gamma value defines how edits applied to an image are spread over its entire tonal range. As you edit an image using 2.2 gamma encoding, corrections appear to produce the same degree of change in shadows, highlights, and midtones. This behavior is known as perceptually uniform, an advantage of synthetic color spaces that are rarely achievable in other color spaces.
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