This document gives a step-by-step description of using ISET to calculate a color correction matrix (CCM). The method described here is the default used by ISET. It is based on (a) simulating the responses to a Macbeth Color Checker under a specific illuminant, and (b) using the simulated sensor responses to derive a 3×3 linear matrix (a CCM) that can be used for Manual Matrix Entry. During the process, several graphs and values of the color accuracy provided by the CCM are calculated.
The methods described in this application note can be used either for a simulated Macbeth Color checker, calculated from the Scene Window, or from a data set loaded from a file – say an image collected by a sensor in the lab. In the example illustrated here, we load the sensor data from a file. If you are working on a simulation, simply simulate the response by creating a Macbeth Color Checker in the Scene Window, set the optics and sensor parameters, and compute the simulated response.
How to Calculate a CCM
We illustrate the calculation using an image of Macbeth Color Checker acquired using a Nikon D70 under a D65 light. To obtain these data, we read the raw image from the Nikon D70 using Nikon Capture. Then, using the ISET script s_NikonD70_Sensor, we convert the NEF file into a Matlab file containing the raw sensor data from the Nikon. The script creates the data file in the form of an ISET sensor structure. The NEF file is large, so we do not include it in the ISET distribution.
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