Canon EOS Rebel XTI - Manual (Page 125)

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Shooting Information Display
Histogram
The brightness histogram display shows the exposure
level distribution, overall brightness and gradation. And
the RGB histogram display is suited for checking the
color saturation and gradation. The display can be
switched with the [x Histogram] menu.
Being able to analyze the histogram and using it to
improve the next shot requires advanced knowledge and
experience. Only a basic explanation is provided here.
[Brightness] Display
This histogram is a graph showing the distribution of the
image’s brightness level. The horizontal axis indicates the
brightness level (darker on the left and brighter on the right),
while the vertical axis indicates how many pixels exist for each brightness level.
The more pixels there are toward the left, the darker the image. And the more pixels
there are toward the right, the brighter the image.
If there are too many pixels on the left, the shadow detail will be lost. And if there are
too many pixels on the right, the highlight detail will be lost. The tones in-between will
be reproduced.
By checking the image’s brightness histogram, you can see the exposure level bias
and the overall tone reproduction condition.
[RGB] Display
This histogram is a graph showing the distribution of the image’s brightness
level of each primary color (RGB or red, blue, and green). The horizontal axis
indicates the color’s brightness level (darker on the left and brighter on the
right), while the vertical axis indicates how many pixels exist for each color
brightness level. The more pixels there are toward the left, the darker and less
prominent the color. And the more pixels there are toward the right, the brighter
and denser the color. If there are too many pixels on the left, the respective
color information will be lacking. And if there are too many pixels on the right,
the color will be too saturated with no detail.
By checking the image’s RGB histogram, you can see the color’s saturation and
gradation condition and white balance bias.
Sample Histograms
Dark image
Normal image
Bright image