Projections

GDDM V3R2 Base Application Programming Guide

Projections

GDDM V3R2 Base Application Programming Guide
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A projection is a sequence of changes to the image, defined by your program, that can be applied during any transfer operation. GDDM lets you define a projection in advance of its use, and independently of the image that it is to act upon. A projection can also be saved and restored.

You can use a projection to perform editing operations on an image during a transfer operation. For example, if you are processing a particular type of legal document, you know that each has some information in common with the rest, such as several paragraphs of legal jargon. They also contain information that is unique to each document, such as names, addresses, and signatures. You are interested only in extracting the unique information, as there is no point in keeping lots of copies of the same thing. You can use a projection to extract just the information you want, maybe from different parts of the document, and exclude the rest. For example, you can then rotate, reposition, or change the size of the extracted information in the target of the transfer operation.

Each individual operation in a projection is known as a transform. A projection containing a transform is illustrated in Figure 24 in topic 6.5. A projection can contain more than one transform. This is illustrated in Figure 25.

A transform is a composite editing function, consisting of several transform elements. GDDM applies the function to the source image, and creates a temporary intermediate image to hold the result of each transform element. The final result is subsequently placed in the target image. The temporary intermediate image is called the extracted image.

Figure 24. Projection containing a transform

Transform elements can define any or all of the following:

Extraction

Defining a rectangular sub-image to be extracted from the source image

Scaling

Changing the size of the extracted image

Rotation

Reorienting the extracted image

Reflection

Flipping over the extracted image

Negation

Converting the extracted image to its "photographic negative."

(There are also three transform elements that specifically relate to scanning. These are covered in "Scanning gray-scale images" in topic 17.2.)

Apart from any transform elements, a transform must contain:

A definition of the location in the target image where the extracted image is to be placed. This definition also specifies how the extracted image is to merge with the target image.
And can contain:
A specification of the pixel generation/deletion algorithm to be used:
- When the size of an extracted image is altered by a scaling operation
- When image data is copied between two images whose resolutions differ.

Transform elements operate on the extracted image in isolation, independent of the target image. Items 1 and 2 above are not called transform elements, because they both affect the way that the extracted image combines with the target image.

Figure 25. Projection containing two transforms

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