Canon CHDK - Manual (Page 25)

Blend
Blend Y
• Histogram mode [Linear, Log] < Histogram parameters < Main Menu
Determines how the Y-axis (vertical) of the histogram will be scaled. Log is useful for
scenes with a large amount of a single color, such as an overcast sky (lots of gray.)
A 10 MP camera might have its Y-axis scaled like this...
Linear Log
10,000,000 pixels
7,500,000 “
6,250,000 “
5,000,000 “
3,750,000 “
2,500,000 “
1,250,000 “
1 “
10,000,000 pixels
1,000,000
“
100,000 “
10,000 “
1,000 “
100 “
10 “
1 “
Show histogram over/under EXP Enable [•] / Disable [ ]
EXP in on-screen display. If parts of a scene are over or under exposed, then this setting will
display “ EXP ” above the histogram, and a red dot at the end that is exceeding exposure limits.
Ignore boundary peaks [
0 – 32
]
Another tool for controlling the scaling of the histogram. If you know that a scene will contain
large amounts of black or white (e.g a moon shot) you can set how many levels from the left or
right edges of the histogram to ignore, if those levels peak in the histogram. This will increase
the visibility of the smaller portion of the histogram.
In this example the image is both over and
under exposed (the scene has a very wide
dynamic range)
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