Deceived by your eyes

In the previous post I developed some test patterns which I claimed consisted of pixel-wide red lines and green blue lines. To make things clearer, I tripled their size on the screen so that you could see the alternate lines.

Now if your eyes work anything like mine, you will readily see that half the lines are blueish, but may doubt that the other half are red. They actually look purple. But it is your eyes that are being deceived. It is the purest of red available from a computer, with the RGB values of #FF0000. That is, the maximum amount of red, and zero blue and green.

Still don’t believe me? Here is the test pattern, but with the left hand side completely filled with the red. Copy this graphic and paste it into your graphics editor of choice. Zoom in and you will see that what looks to be purple is in fact as red as the large section at the left:

Proof that those lines are red, not purple

Or you can just use a magnifying glass to look at this pattern on the screen. The larger you make it look, the more accurate will be your perception of the colour. Moral: it’s unwise to fully trust your own eyes. Actually, the blue stripes are also distorted by our eyes due to their close proximity of the red. Here is the actual blue colour of the stripes:

The real blue 

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Update: Somehow I start this post writing ‘red and green lines’ when clearly I was talking about ‘red and blue lines’.

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