Transform Spatial Coordinates

The purpose of this option is to remap the coordinate system of an image. This rempping process allows simple translations, rescalings and more complex transformations to be produced provided the coordinates in the source image (Iold,Jold) may be expressed in terms of the coordinates of the destination image (I,J) by the mapping

       Iold = iFormula(I,J), Jold = jFormula(I,J).

Buffer containing source image ?

The buffer specified here will be used to define the source image which will subsequently be coordinate transformed. This buffer is also used to define the source and destination windows.

Buffer to write transformed image to ?

The transformed image will be written to the buffer specified here. This may be the same as the source buffer specified above. The destination buffer will be made the current output buffer during the transformation process.

Transform from Window or whole Screen ?

The source image may be confined to a window (<W>) or contain the entire image (<S>). A later prompt determines the action to take if information outside the specified area is required to create the transformed image.

Window Selection: Region to transform from

If the answer to the previous question specified that the transform was to be produced from the contents of a window, then the window selection submenu is produced to enable the window to be specified. Information on operation of DigImage windows may be found under the [H Help] option within the submenu.

Result to Window or whole Screen ?

The resulting transformed image may be written to a window (<W>) or the entire image (<S>). A later prompt determines the action to take if information outside the specified source window/screen is required to create some part of this transformed image.

Window Selection: Region result to be placed in

If the answer to the previous question specified that the result of the transform was to be placed in a window, then the window selection submenu is produced to enable the window to be specified. Information on operation of DigImage windows may be found under the [H Help] option within the submenu.

Formula for the vertical coordinate (Iold) of the pixel in the source window corresponding to the pixel I,J in the destination region ?

Suppose the coordinates in the new and old image spaces are related by

       Iold = iFormula(I,J) and Jold = jFormula(I,J)

where I,J is the coordinate of a pixel in the new transformed image and Iold,Jold is coordinate of the corresponding pixel in the original image. The functions iFormulat(.,.) and jFormula(.,.) give the functional relationship between the two image spaces. The function iFormula(.,.) should be specified at this prompt in terms of I and J, the transformed coordinates.

Formula for the horizontal coordinate (Jold) of the pixel in the source window corresponding to the pixel I,J in the destination region ?

The function jFormula(.,.) should be specified at this prompt in terms of I and J, the transformed coordinates. See entry for previous prompt for further details.

If information outside the source region is required, Set pixels to given intensity or Wrap spatial coordinate ?

Sometimes the formula specified in the previous two prompts will require information on intensities from outside the source region (window or entire screen). If this happens for a given pixel, then the intensity for that pixel may either be set (<S>) to a specified value, or the spatial coordinate(s) of the source window wrapped (<W>).

{If setting intensity for invalid pixel reference}

Set invalid pixel references to what intensity ?

This prompt is produced only if information on pixels outside the source region is requested to produce a destination pixel. The intensity of such a pixel will be set to the value specified here.

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DigImage User Documentation

Stuart Dalziel, last page update: 19 February 1996