Using The Histogram Feature To Adjust Image Contrast - Canon CanoScan FB 1200S User Manual

Using the Histogram Feature to Adjust Image Contrast

The data comprising an image contains a variety of brightness settings ranging from
shadows to highlights. These settings are represented in Plug-in Module CS-S by values
ranging between 0 and 255. The difference in these values determines the image's
contrast. To show how much of the image data falls into each brightness setting,
Plug-in Module CS-S contains a histogram feature that shows this data distribution
clearly. With the histogram you can adjust the level of shadows and highlights to
achieve beautiful tones with the best possible contrast.
Hint
• You can enhance images with the histogram options only when the image has
been previewed in the color or grayscale scan modes.
• You cannot enhance the image with the histogram when ColorSync
How to Interpret Histograms
You can select the entire image or specify an area for which a histogram will be
generated. The height of the peaks of the histogram is directly related to the volume
of data with the corresponding value.
How to Adjust Histograms
To change the contrast in an image, the distribution of data between shadows and
highlights can be adjusted by dragging the shadow and highlight marks at the bottom
of the histogram. All of the data lying to the outside (left) of the shadow mark is
changed to a zero value and all of the data lying to the outside (right) of the highlight
mark is changed to a 255 value. The examples below show adjustments to improve the
contrast. Use the [Auto] setting to adjust the histogram for most jobs
graphs below show images adjusted with the Auto setting.
Image with a bias
IMAGE
toward highlights
1
Move the shadow mark
toward the highlight end.
Portion with
Highlights
Portion with
Shadows
Entire Image
Image with a bias
IMAGE
toward shadow
2
Move the highlight mark
toward the shadow end.
41
41
S T E P 4
TM is selected.
Distribution of data
with a bias toward
highlights.
Distribution of data
with a bias toward
shadows.
Distribution of data
widely distributed
between shadows and
highlights.
(p. 42). The
Image with well
IMAGE
distributed data
3
Move both the shadow and
highlight marks inward.