Gray cards : the 12% - 18% controversy

Started Apr 13, 2013 | Questions thread
xpatUSA Forum Pro • Posts: 13,701
Re: The grey card is a reference for print making

Roland Karlsson wrote:

xpatUSA wrote:

I think we all know that raw data from any camera will not be coded in RGB, but thank you for the reminder ;-). I was never talking about raw data with reference to gray card shots and the resulting histogram therefrom.

Hmmmm ... it fees like we are talking by each other. What histograms? On the camera LCD after taking the image? In SPP? In e.g. Photoshop after converting to TIFF/JPEG? Which one are you referring to?

OK, to keep things nice and simple and to avoid all these question marks in our discussion, let us take the example of a X3F file for a Sigma SD10 shot of a Kodak 18% gray card shot under D50 LED floodlighting with the metering showing 0 EV. Hopefully that is specific enough. If the spctral emission card is played, I also have halogens or an EF-500 flash. Take your pick. Next, we will extract the medium-size preview image from the X3F file. That way, no particular converter will be used and no post-processing will be done. The image will be exactly as God, er, sorry, Sigma created. We will open that JPEG image in ImageJ and we will immediately regard the ImageJ histogram.

Where will the peak value of the distribution lie? You tell me, and then I'll do the test.

Yes, when I said earlier "converted without further processing", I really did mean to imply a neutral image, converted from raw and properly profiled. Or even a neutral jpeg out of a camera, if there is truly such a thing . . .

So ... I assume you meant the histogram for the SPP converted image. Or?

I don't recall saying SPP - so, to simplify that question see my paragraph above.

Don't have LR. I know what ProPhoto is, but I have never heard of Melissa RGB before. Did a brief googling. Yet another color space! Yipie! Seems to be a wide gamut gamma 2.2 color space.

Neither do I, but elsewhere I've read that LR working space is named after a lady engineer at Adobe. The space is ProPhoto but the illuminant is D65 and the gamma is specifically sRGB, not 1/2.2.

courtesy of Wikipedia

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SD9, SD10, EF-500, GH1.

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