User Manual

The TWAIN Interface 21
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When using the histogram, it is very helpful to preview the image. Changes
made to the histogram will instantly be shown on the image in
Preview Window
,
allowing you to immediately judge the effects of the changes.
A histogram is a graphic representation of the tonal distribution (the brightness
and darkness levels) in an image. It plots the number of pixels (dots) at each
brightness level. The histogram displays these levels in 4 different
channel
s.
The x-axis of the histogram graph represents the color values from darkest (0)
at the far left to the brightest (255) at the far right; the y-axis represents the total
number of pixels at that value. A histogram for a dark image shows most of the
pixels at the left side of the graph. A histogram for a bright image is more
heavily weighted to the right side.
To adjust the histogram:
1.
Select the
channel
.
2.
Slide the thumb of
the scroll bar to the right or left
, or c
lick the arrow signs
on the right and left ends.
The current value is shown to right of the scroll bar.
Highlight:
The highlight represents the high (bright) end of the color spectrum. If the
highlight value of the Master channel is lowered to 245, all color values between
245 and 254 will be given the value of 255 (white).
Thus, lowering the highlight of the Master channel brightens the whole picture.
Doing this also increases the color contrast because all the remaining pixels
between the midtone and the highlight will be automatically redistributed over
the midtone to 255 range. This redistribution serves to increase the difference
between shades of color.
If the highlight for one of the Red, Green or Blue channels is adjusted then the
results will only affect pixels of that color or containing combinations of that
color (i.e. Yellow contains Green and Blue and would thus also be affected by