DIY "ExpoDisc" WB Test (?)

[Mark_48]

In another thread I had mentioned making an "ExpoDisc" from a piece of white diffusion plastic from a flourescent lighting fixture. I seem to get fairly good results with it, white appears as white in my images. Would it be a valid check using Photoshop's eyedropper to sample something known in an image to be white and if the resulting RGB values are relatively close to being equal (R215, G218, B213 as an example), would this validate it's ability to be used for white balance?

Understandably the the DIY version couldn't be used for setting exposure since its transmission characteristics aren't known.

[arrgeebee]

Post some examples.

[Big WIll]

Using the lid of an old pringles container also does the job!

However its hard to find one as they are now transparent!

[Mark_48]

Threw this together as a comparison of AWB done by the camera and using the white plastic diffuser for a manual WB. Admittingly WB done manually with the white diffuser does have a bluish cast to it, but was easily corrected in PS. The camera AWB image wouldn't color correct in PS without first doing an Auto-Level correction.

As noted in the image text, the RGB values are shown imposed on the white of the box. Refering to my original post, is this a valid test using sampled RGB values to check how well DIY "ExpoDisc" material corrects WB? I'm thinking it should be, just want some affirmation or suggestions to how I'm doing it.