Autotek autocad raster design 2010 Benutzerhandbuch
Three types of contrast curve are available:
■
A Gamma correction curve is exponential. You can either specify the single
exponent (gamma) value or use an interactive slider to determine the
gamma value.
exponent (gamma) value or use an interactive slider to determine the
gamma value.
■
A Fitted curve is drawn smoothly through points you specify. You can add
or remove points from the curve, and drag them to modify the shape of
the curve.
or remove points from the curve, and drag them to modify the shape of
the curve.
■
A Piecewise Linear curve is constructed of straight-line segments between
points you specify.
points you specify.
You can use a grid as a visual reference for constructing the curve. You can
turn the grid on and off by right-clicking in the curve window and selecting
Grid on the shortcut menu.
turn the grid on and off by right-clicking in the curve window and selecting
Grid on the shortcut menu.
Two sliders under the curve control the lower and upper cut-off points for the
curves. Input values below the lower cutoff point are displayed as 0, while
input values above the upper cutoff point are displayed as 255. Curves can be
saved and imported as Gamma Point List (*.gpl) files.
curves. Input values below the lower cutoff point are displayed as 0, while
input values above the upper cutoff point are displayed as 255. Curves can be
saved and imported as Gamma Point List (*.gpl) files.
Like the other histogram functions, when you are operating on a true color
image, you can choose to manipulate a single color channel, or all three
channels together.
image, you can choose to manipulate a single color channel, or all three
channels together.
NOTE The Tonal Adjustment feature does not apply to bitonal images.
Above the curve window, the histogram window displays input and output
histograms. The input histogram is a graph, shown in gray, representing the
number of pixels in the original image containing each of the given colors.
Similarly, the output histogram previews the number of pixels present for
each of the given colors in the image after the curve is applied.
histograms. The input histogram is a graph, shown in gray, representing the
number of pixels in the original image containing each of the given colors.
Similarly, the output histogram previews the number of pixels present for
each of the given colors in the image after the curve is applied.
By default, the histogram window adjusts the vertical scale of the histograms
such that the entry with the highest frequency extends to the top of the
histogram window. You can use the vertical scale slider to effectively zoom
in on the histogram. As you move the slider upward, the scale is increased so
that low frequency values are more visible and high frequency values are
truncated by the top of the window.
such that the entry with the highest frequency extends to the top of the
histogram window. You can use the vertical scale slider to effectively zoom
in on the histogram. As you move the slider upward, the scale is increased so
that low frequency values are more visible and high frequency values are
truncated by the top of the window.
To adjust the image contrast curve
1 Click Image menu ➤ Image Processing ➤ Histogram.
The following prompt appears:
102 | Chapter 6 Modifying Images