the last word

In this post , I looked for drop offs in chromaticity in the octave or two before the highest image frequencies, and failed to find them. Some had hypothesized that such a drop would be a reason for the relative undersampling of chromatic versus achromatic information in the Bayer Color Filter Array (CFA). I did find… [Read More]

Let’s look first at the drop in luminance contrast sensitivity at low spatial frequencies. That’s why dodging and burning works. Slow changes in luminance are introduced by the printer (in the old days) or editor (now) so that local contrast can be higher or to call attention to or from image elements. Done right, the… [Read More]

Yesterday, I presented material on how people’s ability to perceive small – and not so small – luminance changes varies with spatial frequency. Today, I’ll talk about how our ability to perceive changes in chromaticity (color without luminance) varies as spatial frequencies are manipulated. Yesterday, I started with the graphs and followed up with the… [Read More]

We’ve seen that the sensitivity to luminance variation falls off as the luminance spatial frequency increases. If turns out that it also falls off as spatial frequency decreases, giving a band-pass filter effect, which sharpens edges, and gives rise to the Mach Banding that we’ve been looking at in the preceding posts. There are many… [Read More]

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… [Read More]