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80 2 Image formation

(a) RGB (b) R (c) G (d) B

(e) rgb (f) r (g) g (h) b

(i) L* (j) a* (k) b*

(l) H (m) S (n) V

Figure 2.32 Color space transformations: (a–d) RGB; (e–h) rgb. (i–k) L*a*b*; (l–n) HSV. Note that the rgb,
L*a*b*, and HSV values are all re-scaled to fit the dynamic range of the printed page.

to the gamma-compressed R’G’B’ system we mostly deal with, since both have a fractional
power scaling (which approximates a logarithmic response) between the actual intensity val-
ues and the numbers being manipulated. As in all cases, think carefully about what you are
trying to accomplish before deciding on a technique to use. 24

2.3.3 Compression

The last stage in a camera’s processing pipeline is usually some form of image compression
(unless you are using a lossless compression scheme such as camera RAW or PNG).
All color video and image compression algorithms start by converting the signal into
YCbCr (or some closely related variant), so that they can compress the luminance signal with
24
If you are at a loss for questions at a conference, you can always ask why the speaker did not use a perceptual
color space, such as L*a*b*. Conversely, if they did use L*a*b*, you can ask if they have any concrete evidence that
this works better than regular colors.