Computer Vision
Image Representation
A photograph in memory is a grid of whole numbers and nothing else. Move the magnifier and the patch under it appears as a picture and as its numbers at the same moment. Then take the numbers apart: one channel at a time, and fewer and fewer values each.
redgreenbluethe patch under the magnifier
Move the pointer over the photograph to take the magnifier with you
One photograph—
—
Photo
What is shown
The patch
2 values256 values
Values
pixels in the photo—
numbers stored—
values one number can take—
size, uncompressed—
under the magnifier—
centre pixel: light emitted, share of 255—
What to observe
- Move the magnifier. The table of whole numbers on the right is not a description of the patch: it is the patch, and nothing else is stored.
- Show red alone: a grey picture, as are green and blue. A colour pixel is a triple, and the colour lives in the ratio between the three.
- Drag bits per number down. Around four bits the smooth areas break into bands, at one the photograph is a stencil.
- A number is a code, not an amount of light. Grey 128 looks roughlyhalfway but emits only about 22% of the light of 255 (sRGB); the readout shows the light behind the centre pixel.
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