1.10.10.4: Partitive mixing in space for light
- Page ID
- 128493
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)4.1 Partitive mixing from adjacent regions on a computer screen.
The figure below shows three squares containing chequerboard patterns made from red/green, green/blue and blue/red. When viewed from close to the screen, the colours are quite distinct. Now start to move away from the computer screen. As the individual red and green squares become smaller, the left hand square should start to appear yellow. Eventually, once the individual red and green squares can no longer be resolved, the square should appear to be a dark yellow colour. (If you have a small room or insufficient space, reduce the size of the images on the screen).
The left hand square will not appear like the bright yellow you would normally expect on the screen. This is because yellow would normally be produced by the red and green sources within each individual pixel, whereas for the chequerboard patterns you only using only red in some pixels and only green in the others. Consequently you are combining only half the red and green when compared with the normal screen yellow; effectively you are mixing the yellow with black.
This exercise can now be repeated with the green/blue and blue/red chequerboard patterns. You can make up your own patterns to investigate mixing other colours.
This exercise can also tell you something about the spatial resolution of your visual system – more of this in a separate set of experiments.
4.2 Partitive mixing using different screen pixels
Your computer screen uses this partitive mixing in space to produce a huge number of colours. The individual light sources are very small (otherwise they would be noticeable), but they can be seen using a powerful magnifying glass, or a simple pocket microscope or magnifier. These microscopes are plastic with a magnification around 20X to 30X and usually cost around A$10 to A$20. Probably one of the cheap USB microscopes that are now available would also suffice.
The photographs below show the computer screen when photographed through one of these small pocket microscopes. In each case not only the individual pixels that generated the colour be seen through the eyepiece of the microscope, but also the screen colour produced by these pixels can be seen around the edge of the microscope.
Red, green and blue are produced by activating only a single colour in each pixel.
To produce any other screen colours, at least two colours need to be activated within each screen pixel. The following photographs show how yellow, magenta and cyan are produced.
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These individual colours within each pixel can also become visible if very small (and I mean very small) droplets of water are present on the computer screen. Each droplet can then act as the lens of a primitive microscope. I often notice this when use a very fine sparay of window cleaner to clean the computer screen.