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Image Editing
Chapter 4
IMAGE EDITING
Having obtained an image this chapter deals with manipulating that image. The
topics covered involve the use of editing tools for direct adjustments; simple
transformations to adjust the whole image; and colour manipulations to modify the
appearance. It also covers methods to transfer information between layers enabling
the image to be broken down into parts.
Introduction to Raster Editing
It is often desirable to be able to make alterations to the raster image before printing
in order to improve the final result. Some of these corrections can be quite minor,
for example, erasing unwanted pixels causing spreading or merging of lines due to
smudges in the original scanned drawing.
At other times, raster drawings may need major alterations, such as the deletion of
a large area.
Raster images can be modified by using
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Colour manipulation
Drawing tools,
Fence operations,
Layer separation operations
Simple Transformations
These are discussed individually in the following sections.
Invert
This operation behaves differently depending on the type of layer being inverted. If
the layer is 4 bit or 8 bit colour then the data is left untouched but the palette for
that layer is inverted so that red becomes cyan, blue becomes yellow etc.
Technically what happens is that every intensity definition within the palette is
subtracted from 255. For all other layers the data is modified so that for
monochrome the background and foreground is swapped; with grey scale the
intensities are inverted (every pixel is replaced by 255 minus itself); and for 24 bit
colour each colour component is inverted. It is generally used only once with
monochrome layers to rectify the foreground/background colours of an image to
suit Deskan v7.1’s convention. (see “Colour, Palettes and Transparency”, p 2-15)
An example of this is the scanning of old-style blueprints. These drawings are white
on a blue background, and when scanned result in a “black-on-white” image which
has to be inverted.
An important point to remember with monochrome layers is that they can look
right but still be inverted. The solution to this problem is to check the background
appearance colour in Colours - Base Colour - Select. The layer’s background will
always match this colour.
January 2009
Deskan v7.1
4-1