Brightness matching experiment:
Using Photoshop I made six rectangles of 450 by 220 pixels. One half of each rectangele was filled with one of six colors, and the other half of the rectangle was filled with gray. A plastic tube was placed over
each rectangle so the brightness of the color and gray could be compared side by side (as shown above.) The brightness of
the gray section was adjusted with Photoshop's 'Lightness' control in the 'Hue and Saturation' dialog, until the brightness
of the gray matched the brightness of the color. The brightness of the gray was then read with Photoshop's 'Info' tool.
In the Hue-Saturation-Luminance
colorspace, the luminance parameter approximates the visual brightness of the color. The Luminance values (as calculated by
Photoshop) are compared to the brightness that I estimated with my own vision:
| Color | RGB | est.
bright | lumin. | Δ |
| Red | FF0000 | 53% | 57% | 4 |
| Yellow | F6FF00 | 80% | 95% | 15 |
| Green | 00FF00 | 62% | 79% | 17 |
| Cyan | 0087F9 | 56% | 62% | 6 |
| Blue | 0000FF | 46% | 51% | 5 |
| Magenta | FF0081 | 48% | 52% | 4 |
These data are illustrated by the following graph:
In the top portion, my estimated brightness is plotted with blue circles and the
calculated luminance values are plotted with red triangles. In the bottom portion, the delta
value - the difference between the luminance of the color and my estimated matching gray brightness - is plotted
with black Xs. The Y axis is percent.
Notice the close agreement between brightness and luminance for red, cyan, blue and magenta. On the other hand,
my estimates for yellow and green are dimmer than their luminance would predict. This is consistant with deuteranopic
colorblindness, which I have been aware of since second grade.
Here are some links:
Ishihara color vision test
Vischeck colorblindness simulation software
Visually harmonius color mixing software
Additive and subtractive color mixing
Color space geometry explained
Jentronics color space conversion software
And, as promised, tetrachromatic mutant women.
Next: Opponents, rods and Goethe's hypothesis.
(continued...)
Jerry Halstead has been sending up suborbital water rockets - with cameras! His Quicktime movies remind me so much of the pre-Allen Sheppard space shots of the very early 60s, complete with sound track.
I love it!
Emerging photography superstar and blogger Julius Welby points to the winners of a lunar eclipse photo contest.
