Editing color images
Brief
description: This section is devoted to ways of
enhancing color and greyscale raster images. There are several utilities
for correcting such things as image brightness, contrast, hue, and saturation;
correction by histogram, and filtration. You will also learn about converting
images to RGB, 8-bit indexed and greyscale and converting color and greyscale
images to monochrome layers.
Correcting
image brightness, contrast, hue, and saturation
You
can tune the brightness, contrast, hue and saturation of color and greyscale images.
Choose Brightness/Contrast
from the Image menu.
Using
the Brightness/Contrast
dialog, you can tune:
- The brightness of
color and greyscale images
- The contrast of
color and greyscale images
- The hue of color
images
- The saturation of
color images
You
can tune the parameter value by using the sliders or by entering the values
in the corresponding fields.
Correction by
Histogram
Using
correction by histogram you can tune the image brightness, hue and contrast.
You can apply automatic correction or tune the parameters manually.
Choose
Equalize
from the rImage menu.
To correct
an image by histogram automatically, press Auto on the Equalize dialog.
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To correct an
image manually you need to specify three values: lightest and darkest
levels, and image gamma - for each channel or for Master channel.
- The darkest
level (the left slider position) is set with the dark eyedropper
 ,
using which you can specify the colors to turn black.
All pixels included in the histogram area from 0 to the left slider,
will turn black.
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- The lightest
level is set with the light eyedropper
 ,
using which you can specify the colors to turn white.
All pixels included in the histogram area from the right slider
to 256, will turn white.
- Using the middle
slider, specify the value of image gamma.
- Moving
the middle slider to the left increases the gamma value; the
image becomes lighter.
- Moving
the middle slider to the right reduces the gamma value; the
image becomes darker.
- When you achieve
satisfactory results in the Preview window, press Apply.
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Color filters
Blur
This
filter produces a blur effect on an image. For example, you can apply
the Blur filter to an image area that has texture fills.
Choose Blur
from the rFilters menu.
- Set the
Radius value for the filter. Increasing the Radius value increases image
blurring. To modify the Radius value, use the slider or enter
a value in the field.
- When you achieve
satisfactory results in the Preview window, press the Apply
button.
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Unsharp Mask
This
filter is designed to increase the
sharpness of color boundaries, producing an overall increase of image
sharpness. This filter can be used to correct images that became blurred
after interpolation - e.g., after such operations as rotate,
scale, alignment, calibration or
four-point calibration, and
also resize and resample.
Choose
Unsharp
Mask from the rFilters menu.
- Set Radius - "level" of
the filter effect. Increasing the Radius value increases the number
of pixels surrounding the color transition boundary that are to
be processed.
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- Set Sensitivity for the filter using the slider or enter the value
in the corresponding field. Increasing this value provides a stronger
effect.
Applying small Radius values
result in an increase of sharpness only on color boundaries.
- When you achieve
satisfactory results in the Preview window, press the Apply
button.
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Median
This
filter reduces image noise by analyzing all pixels within the specified
radius and assigning the central pixel with the averaged value of the
reviewed pixels. As a result, pixel color and brightness are evened. For
example, the Median filter can be used to eliminate image "grain".
Choose
Median
from the rFilters menu.
- Set the
Radius value for the filter
- this is the area within which color values will be analyzed.
- When you achieve
satisfactory results in the Preview window, press Apply.
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Convert
to RGB, greyscale, 8-bit indexed
Convert to RGB (greyscale)
- If your document
contains several raster images, select the one(s) to convert to RGB
(greyscale).
- From the rImage
menu, choose Convert to, and then Convert to RGB (Convert to greyscale).
Convert to 8-bit indexed
You
can convert full-color images (24 bit per pixel) and monochrome images
to 8-bit indexed (8 bits per pixel).
This
operation can be used to reduce the size of a full-color file, and therefore
speed up operations when working with it. Note, that in some cases the
converted image might have lower quality due to some information loss.
- If your document
contains several raster images, select the one(s) to convert to 8-bit
indexed.
- From the rImage
menu, choose Convert to, and then Convert to 8-bit indexed.
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Execution order
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Press Set auto palette
 .
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Recalculating of palette for specified color number
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Specify
the color number in the Colors  field
Press
the Reset Palette 
button.
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Selecting colors from the palette
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Press Shift, select colors from the palette by clicking on them (if only selecting
one color there is no need to press Shift).
NOTE:
Select the Light
Paint checkbox 
button to view selected colors in the Preview window.
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Merging selected colors
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Press Merge Colors  button.
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Deleting selected colors
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Press Delete Colors  button.
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Changing selected color(s)
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To change selected color(s):
To the specified color - Press Get color to set 
and choose a desired color from the Color box.
To one color of the image - press the button with eyedropper
, and then specify a desired color on the screen.
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Adding color(s) to the palette
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Enter
desired number of colors in the Colors field.
Press Set auto palette
- or -
Click on a blank palette cell. Click on the added field, and assign the color
as described above in section Changing selected color(s).
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