18% Gray Card - How to make

Started Oct 27, 2002 | Discussions thread
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DomT
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18% Gray Card - How to make
Oct 27, 2002

I tried to make a 18% grey card for white balance. In PhotoShop Colorpicker, I pick C=0, M=0, Y=0 and K=18%, then RGB turns out to be= 213, 215, 216 respectively.

But if I calculate using RGB instead of CMYK, I get (255 x 18% = 209.1). So should RGB = 209, 209, 209? Even if I use 256 x 18% it is still only 210. What gives?

Worse still, if I chose Image, Mode, Grayscale then print out my card, when I look under a magnifying glass it is made up of coloured dots, not just spaced grey dots. I'm using an Epson 740 printer.

So how do I make a 18% card? Do I believe CMYK or RGB? How do I make the Epson print with black ink?
Any suggestions appreciated.
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