For a color image, say with dimensions 320 by 240, we have 76,800 pixels in the image. What does each pixel represent for a color image? Is it just the RGB values for that pixel? How are shapes and textures represented in pixels? If each pixel in a colored image only contains RGB values, is that information enough to store the shape, size, and texture of the objects in the image?
2 Answers
A single pixel in RGB space can only hold information about the color value of that single pixel.
Shapes, and textures can only be described with the combination of several pixels, that information is not stored in single pixels themselves.
Moreover this information (same as for shape, size, texture of possible objects) is never stored explicitly in the image data. You can infer shapes or textures based on your interpretation of underlying pixel data, but this always depends on how you yourself define a shape or a texture.
Every pixel contains a simplified representation of the light landing on the corresponding sensor cell in the camera. The amount of light is averaged over the cell area, and light spectrum is grossly described by taking three weighted averages of intensity over the frequencies. The result is (usually) three integers in the range 0-255, for a total of 24 bits of information.
As the pixels are aligned on a grid, a digital color image can be seen as a triple matrix of integers, that's it. (Below, an example of such a matrix.) This information is raw.
The semantic image content must be inferred by an image analysis system, which is able to segment the image in distinct areas, and to a lesser extent, characterize the textures.
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