I reworked the luminance step wedge of yesterday’ post so that it consists of 10 Delta-E steps from zero to 80 along the gray (a* = 0, b* = 0) axis:
The Mach Bands are evident.
Then I created a similar image, with L* = 50, b* = 0, and a* starting at -40 and proceeding upwards in steps of 10 Delta-E:
The Mach Banding effect is greatly reduced on my calibrated monitor. The literature says that the effect is non-existent for changes in chromaticity with no changes in luminance, so I suspect that what I see is due to a combination of a) imperfect calibration of my monitor, b) imperfections in the CIELab color space, so that there is actually a luminance change between various samples with the same L* value and different a* and b* values, and c) my eyes being somewhat different from the 1931 CIE observer.
For completeness, here is an image with L* = 50, a* = 0, and b* starting at -40 and proceeding upwards in steps of 10 Delta-E:
Now, let me present all three images at reduced size:
Back up until you can’t see the steps in the two images with (putatively) no luminance change. Can you see the steps in the image with only luminance change? Yes you can.
Now you know three more things about spatial effects in color vision.
- There is very little differentiation for chromaticity changes at any scale.
- At the spatial frequencies get higher, there is a point where chromaticity sensitivity begins to drop.
- That point occurs at lower spatial frequencies than the similar drop in sensitivity that occurs for luminance.