White card doesn't work too well for me, my pictures still carry a small amount of yellow tint. Didn't wanna waste $$ on buying grey card so I thought maybe I could do this:

1) launch photoshop
2) create a new layer
3) click on the color picker and choose CMYK 12% or 18%
4) get the picture developed in a matt photo paper

viola, your gray card is done, and will cost you no more than a 4X6 print...of course unless you decide to print it at larger format now hopefully the photolab's machines comply with ANSI standard.

I haven't done this, but will be doing it....still looking for a reliable photolab here.

What you see on photoshop doesn't matter at all because you are not arbitrarily picking a grey color depending on your monitor, room lighting, and etc (just load up sRGB color profile in photoshop). Setting the CMYK at the respective % will give you precisely the % of grey regardless of what you see on your monitor. The most important part is, of course like I mentioned, the photolab better have their machines calibrated according to ANSI standard, if they do, you'd get the the % of gray you set in photoshop. You can always make a few prints from different shops and see if they come up pretty much the same. And also, the photopaper quality do matter. Some of the shops here use some really crappy Kodak photo paper, they are so thin that you can see through the photo...

But anyway, the precise % is not really important, after all, some argue that camera manufacturers don't really use 18% gray to tune the meters.

EDIT: oh btw, this is assuming that you are developing the photo at a photolab, I thought that was very apparent, but if you wanna print them at home, you do need to calibrate the printer properly.

This post has been edited by AlamakLor: Mar 22 2007, 03:11 AM