Interpreting White and Black Point Targets

Base Values

The base values consist of the maximum white (R255, G255, B255) for white point evaluation or the maximum black (R0, G0, B0) for black point evaluation. The base values allow comparison with the specific test value, for example, 240 in the example to the left. A visual determination of where separation from the maximum white point or maximum black point occurs can be made by comparing the test value to the base value. The image to the left shows the base value for white point evaluation (255 RGB) shaded in blue. The checkerboard pattern allows for more precise comparison of the values.

Visually Comparing Specific Test Values to the Base Value

To determine where the first ink becomes visible in the highlights, visually compare the specific test values to the white point base value—255 RGB. Most ink-jet printers will not produce a discernible white point until about 250 RGB. Again, many variables affect the white point, most importantly the media used. The image to the left illustrates the comparison of the specific test value (240) to the white point base value of 255 RGB.

On the next page, we will take a closer look at relative values and grayscale neutrality.

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