Histogram - Canon Camera Hackers Manual

The entries Max ISO HI and Max ISO AUTO are used to limit the maxi-
f
mum ISO chosen in the respective ISO mode, and thus to limit visible
noise in the image. This value must not exceed the maximum ISO speed
physically possible for your camera
tiplied by 10, so, for ISO 800, dial 80.
In Min ISO you should set the minimum ISO physically possible for your
f
camera. Again, the values dialed in here are multiplied by 10, so, for ISO
100, dial 10.

4.3.3 Histogram

Your camera probably does have a histogram, at least in Review Mode.
However, this histogram is only shown after an image has been taken.
The CHDK has a bit more to offer. One option is showing a Live Histo-
gram on the display. The histogram can be shown when the shutter button
is half-pressed (Shoot) or always. So, with a quick look at the histogram, you
can decide whether the image is correctly exposed or whether it is neces-
sary to adjust the exposure (see section 4.3.1 for the fast Ev buttons). In the
case of too much contrast, however, it would be better to shoot an HDR
bracketing series (section 4.6.2).
There is a lot to configure:
Different histogram styles can be chosen in the entry Histogram Layout
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(Figure 4-21):
RGB Displays the sum of the red, green, and blue pixel values.
Y Displays the luminance component.
RGB Y Displays RGB above luminance.
R G B Three histograms, one for each color.
RGB all Displays all five histogram types with RGB on top.
Y all Displays all five histogram types with luminance on top.
Blend Blends the three histograms of R G B into one.
Blend Y Same as Blend, but with the luminance histogram added below.
Histogram Mode allows you to choose between Linear and logarithmic
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(Log) scaling of the histogram Y-axis. Logarithmic scaling can be useful
if the image contains a large amount of similar colors. With linear scal-
ing, this would result in very high peaks.
When enabled, Show Histogram Over/Under EXP displays red dots at
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both ends of the histogram if over- or underexposed areas are detected,
as shown in some histograms in
3 For the real limits of your camera please see
CameraFeatures.
3
. The values dialed in here are mul-
Figure 4-21.
http://chdk.wikia.com/wiki/
4.3 Exposure
Figure 4-20
The CHDK histogram can be configured
through submenu Histogram.
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