Btw, how did you make the basis color chart? If I make a graduation from (0,64,255) - (255,64,0), then I don't get any green, like you got in the upper left corner.
I set (almost) arbitrarily G=64 since I knew the higher sensitivity of the sensor for the G channel would produce seeing a pure gray at some R&B dominant point.
Regarding the gradation, R and B are independent of each other: R runs 0 to 255 left to right, and B runs 0 to 255 up to down, so top left corner is pure green (0,64,0), and (64,64,64) is the gray point for this test chart. All that is clearer looking at the Hue distribution of the test chart:
Find here the test chart in 1024x1024 size: [a href=\"http://img520.imageshack.us/img520/6944/cartag64zs5.jpg]CARTA DE PRUEBA G64[/url]
I don't recommend you to print the charts but shoot them straight on your monitor instead.
This will not invalidate the procedure at all as long as the magenta chart is shot under the same conditions (monitor settings + room light conditions) as the test chart
Thus your monitor does not need to be calibrated at all (mine is not), and your room's light conditions can also be any as long as they remain constant (be careful with sunlight entering your window, these experiments are best done at night).
You will even be more precise this way, and you will save time and ink!
BTW I have been told Nikon cameras (from D200) can do this by simply configuring the so called 'UniWB' white balance mode in the camera. No idea how difficult is that.
PS: this is a sample shot using the custom WB achieved, comparing the result of developing the same RAW file:
- Left: with its embedded WB from camera (i.e. our specific neutral WB)
- Middle: no WB at all (forcing 1.0 multipliers in DCRAW)
- Right: Daylight WB preset
First 2 images match very well as expected.
In my first quick tests, blinking areas in the camera's display (350D) are very close to real RAW blown areas. In fact, surprisingly they are a little bit more optimistic than a strict partial saturation detection over the RAW data. So watch out!.
Whether this happens or not depends solely on the 350D's implementation of the blinking highlights; the WB calculation procedure is conceptually flawless.