S-CIELAB calculations: Define spatial calibration

Defining spatial calibration information

Now, we need to specify the viewing conditions. Specifically, we need to know the relevant spatial parameters for when the digital image is viewed. This parameter tells us how many digital samples there are per degree of visual angle. We call it sampPerDeg. For a typical monitor (72 dots per inch) viewed at 18 inches, one inch sweeps out:
(180/pi) * atan(1/18) = 3.1798 deg.
Hence, there are 72/3.1798 samples in a single degree of visual angle for this monitor.

In Matlab, this is computed as:

sampPerDeg = round(72 / ((180/pi)*atan(1/18)));

Or, you can use a ready-made function in the S-CIELAB distribution:

sampPerDeg = round(visualAngle(-1, 18, 72, 1));

Either way, the result for this example should be:

sampPerDeg = 23.

The next step is to specify color calibration information.