Sample size is an important consideration when measuring any reflectance accurately. Accurate measurement is absolutely critical to evaluating reflectances, which is obvious to everyone, once considered. However, some shooters never change the sample size. Changing the sample size should be a matter of course for certain kinds of reflectances.
What does the term sample size mean? It’s the sample area chosen for your evaluation of the reflectance you place your cursor on. When you see a sample size value it’s really the bounding value of a square. You may be used to Photoshop’s three sample sizes: 1x1, 3x3, and 5x5. Photoshoot™ software allows 1x1 to 21x21 in single pixel increments. Choose the appropriate size for accurate evaluation of important reflectances. Zoom in to the pixel level and count (or guess) the number of pixels you’re interested in obtaining information on. Plug in the value and read the reflectance.
Why would you change the sample size? That depends on what kind of information you’re interested in obtaining. When you’re trying to evaluate the repeatability of your strobes you’ll want a 1 pixel sample size to make sure you’re getting a single pixel reading. If you’re performing a Setup>Balance use a size more like 7 or 9 pixels. If you’re reading a general fabric texture use a number like 21, if you’re reading the highlight to shadow difference of that fabric (to see if the texture will repro), you might want a 1 or 3 pixel sample. Because there are 21 different choices, use the one that’s right.
In the lower left image, the sample size of 9 is not appropriate to discern if the shingles will separate on press. A sample size of 1 would be the right choice here. In the lower right image we’ve chosen a sample size of 1 to check the printability of the creases on the Martian woman’s face. The crease reads 43% and the blue-green “flesh” reads 18%, clearly enough separation to visually render on press.
Change the sample size in the Preferences dialog box, Setup>Preferences> Sample Size. Find the Sample Size dialog box along the right side, about halfway down. Enter any change with your keyboard and click OK to confirm your selection. Verify that sample size along the bottom of the Photoshoot™ interface. Sample size should be considered when performing a Neutral Program or Tone Correct remap. Zoom in, evaluate the size you need and use the sample size that’s right.