Abstract
In the first two chapters the presentation was restricted to gray-scale images, but, as you might have noticed, the real world consists of colors. Going back some years, many cameras (and displays, e.g., TV monitors) only handled gray-scale images. As the technology matured, it became possible to capture (and visualize) color images and today most cameras capture color images. In this chapter the focus is on color images. The nature of color images is described together with how they are captured and represented. Hereafter the photoreceptors in the human eye and their relation to the color spectrum are presented together with the two fundamentally different ways of describing colors, namely the additives colors and the subtractive colors. Lastly the definition and representation of an RGB color image and its relation to other color representations, such as HIS and rgI, are laid out.
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Notes
- 1.
An image histogram is defined in the next chapter.
- 2.
Note that the formula is undefined for (R,G,B)=(0,0,0). We therefore make the following definition: (r,g,b)≡(0,0,0) when (R,G,B)=(0,0,0).
- 3.
If r and g need to be represented using one byte for each color we can simply multiply each with 255 and the new values will be in the interval [0,255].
- 4.
It should be noted that the naming of the different color representations based on hue and saturation is not consistent throughout the body of literature covering this subject. Please have this in mind when studying other information sources.
- 5.
Note that sometimes all parameters are normalized to the interval [0,1]. For example for H this is done as \(H_{\mathrm{normalized}} = \frac{H}{360}\).
- 6.
When going into color perception and color understanding even more terms are added to the vocabulary.
References
Bowmaker, J.K., Dartnall, H.J.A.: Visual pigments of rods and cones in a human retina. J. Physiol. 298, 501–511 (1980)
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© 2012 Springer-Verlag London Limited
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Moeslund, T.B. (2012). Color Images. In: Introduction to Video and Image Processing. Undergraduate Topics in Computer Science. Springer, London. https://doi.org/10.1007/978-1-4471-2503-7_3
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DOI: https://doi.org/10.1007/978-1-4471-2503-7_3
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