AccuColor – Chart

The “chart” mode has one input: a multiband image of the whole color checker chart, with all 24 patches visible. For an overview of all modes, see AccuColor.

In the “roi” box, enter four windows, one on a patch at each corner of the chart, in this order: upper left, upper right, lower left, lower right, with the gray patches in the bottom row. That is 16 numbers in total, separated by spaces, and all four windows must be the same size. You can draw the windows on the chart image in Show; see Window Arguments. From these four windows, AccuColor finds all 24 patches.

• AccuColor computes the calibration matrix and copies it to the system clipboard. It is only stored there temporarily, so save it right away: paste it into a text file, or into the “calibration” box of AccuColor in “input” mode. See Input.
• The default “output” is a map: the chart image with the measured regions of the 24 patches filled in, so that you can check the measurements were made where you expected.
• The other “output”, measurements, is only needed to verify the calibration. Choose the “patch values”: sensor (the readings of each patch, as a 6 × 4 image), or the computed XYZ, Lab or ΔE values (as 1 × 24 images). ΔE is the error in each output color; values under 2.3 are indistinguishable from the true colors. You can view these values with Print.

The chart image must have more than 3 bands, covering the visible spectrum, with no infrared or ultraviolet bands. The calibration matrix only works on images with the same bands, in the same order.

Special thanks to Ken Boydston and Brian Amrine of MegaVision.