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Images

Basic Image Operations

(image-new width height)
MediaScheme GIMP Procedure. Create a new image of specified width and height.
(image-load filename)
MediaScheme GIMP Procedure. Load an image from a file. The name of the file is a string (and, unless a named value, typically surrounded by quotation marks).
(image-save image fname)
MediaScheme GIMP Procedure. Save image in the specified file (which should provide the full path to the file). The type of the image (JPEG, GIF, PNG, etc.) is determined by the suffix of the file name.
(image-show image)
MediaScheme GIMP Procedure. Opens a new window with the image.
(image-height image)
MediaScheme GIMP Procedure. Determine the height of the given image
(image-width image)
MediaScheme GIMP Procedure. Determine the width of the given image.

Basic Drawing Operations

(image-blot! image col row)
MediaScheme GIMP Procedure. Draw a spot in image at (col,row) with the current brush and foreground color.
(image-draw-line! image col1 row1 col2 row2)
MediaScheme GIMP Procedure. Draw a line in image from (col1,row1) to (col2,row2). Uses the current brush and foreground color.

Pixel-Based Operations

(image-get-pixel image column row)
MediaScheme GIMP Procedure. Get the pixel at the specified position in the image.
(image-set-pixel! image column row rgb-color)
MediaScheme GIMP Procedure. Set the pixel at the specified position to the new color.
(image-transform-pixel! image column row func)
MediaScheme GIMP Procedure. Modify the pixel at (col,row) in image by applying func to its old color and setting that pixel to the resulting color.

Higher-Order Procedures

(image-calculate-pixels! image fun
MediaScheme GIMP Procedure. Fills in all the pixels in the image by setting the color at each position to the result of applying fun to the column and row. fun should have the form (lambda (col row) color). Unlike image-compute-pixels!, which can compute pixels in any order, image-calculate-pixels! is guaranteed to do a row-by-row, left-to-right scan through the image. However, image-calculate-pixels! is likely to be slower than image-compute-pixels! (although faster than coding the iteration yourself).
(image-compute pos2color width height)
MediaScript GIMP Procedure. Create a new width-by-height image by using pos2color (a function of the form (lambda (col row) color)) to compute the color at each position in the image.
(image-compute-pixels! image pos2color)
MediaScheme GIMP Procedure. Set each pixel in the image to the result of applying function to the position of the pixel. function must have the form (lambda (col row) expression-to-compute-color).
(image-redo! image fun)
MediaScheme GIMP Procedure. Scans through the image, replacing the color at each pixel in the selected region (or the whole image, if nothing is selected) with the result of applying fun to the column, row, and current color at each position. fun should therefore have the form (lambda (col row color) newcolor). If fun returns IRGB-TRANSPARENT, leaves the pixel unchanged.
(image-scan image proc!)
MediaScheme GIMP Procedure. Scans through the image, applying proc! the the column, row, and color at each position. proc! should have the form (lambda (col row color) ...). In contrast to many of the other image iteration procedures, image-scan is guaranteed to scan row-by-row from top-to-bottom, scanning each row from left to right.
(image-transform! image fun)
MediaScheme GIMP Procedure. Transform image in place by setting each pixel to the result of applying fun to that current pixel color.
(image-variant image fun)
MediaScheme GIMP Procedure. Create a new image of the same width and height as image, each of whose pixels is computed by applying fun to the color of the corresponding pixel in image.
(region-calculate-pixels! image left top width height fun
MediaScheme GIMP Procedure. Creates a region of the image by applying fun at each position in the region. fun should have the form (lambda (col row) color). Unlike region-compute-pixels!, which can compute pixels in any order, region-calculate-pixels! is guaranteed to do a row-by-row, left-to-right scan through the image. However, region-calculate-pixels! is likely to be slower than region-compute-pixels! (although faster than coding the iteration yourself).
(region-compute-pixels! image left top width height pos2color)
MediaScheme GIMP Procedure. Create a portion of an image by setting each pixel in the specified region to the result of applying function to the position of the pixel. function must be a function of the form (lambda (col row) expression-to-compute-color).
(region-scan image left top width height proc!)
MediaScheme GIMP Procedure. Scans through a region of the image, applying proc! at each position in the region. proc! should have the form (lambda (col row color) ...). In contrast to many of the other region procedures, region-scan is guaranteed to scan row-by-row from top-to-bottom, scanning each row from left to right.

Selection Procedures

(image-select-all! image)
MediaScheme GIMP Procedure. Selects all of the pixels in the image.
(image-select-ellipse! image selection-type left top width height)
MediaScheme GIMP Procedure. Select an ellipse whose left margin is left, top margin is top, width is width and height is height. If selection-type is REPLACE, the ellipse replaces the current selection. If selection-type is ADD, the ellipse is added to the current selection. If selection-type is SUBTRACT, the ellipse is subtracted from the current selection. If selection-type is INTERSECT, the ellipse is intersected with the current selection (that is, only points that are in both the current selection and the ellipse remain selected).
(image-select-inverse! image)
MediaScheme GIMP Procedure. Selects the inverse of all selected images in the image.
(image-select-nothing! image)
MediaScheme GIMP Procedure. Clears the current selection. Afterwards, nothing is selected.
(image-select-polygon! image selection-type positions)
MediaScheme GIMP Procedure. Select a polygon described by the given list of positions (each created by position-new). If selection-type is REPLACE, the polygon replaces the current selection. If selection-type is ADD, the polygon is added to the current selection. If selection-type is SUBTRACT, the polygon is subtracted from the current selection. If selection-type is INTERSECT, the polygon is intersected with the current selection (that is, only points that are in both the current selection and the polygon remain selected).
(image-select-rectangle! image selection-type left top width height)
MediaScheme GIMP Procedure. Select an rectangle whose left margin is left, top margin is top, width is width and height is height. If selection-type is REPLACE, the rectangle replaces the current selection. If selection-type is ADD, the rectangle is added to the current selection. If selection-type is SUBTRACT, the rectangle is subtracted from the current selection. If selection-type is INTERSECT, the rectangle is intersected with the current selection (that is, only points that are in both the current selection and the rectangle remain selected).
(image-fill-selection! image)
MediaScheme GIMP Procedure. Fill the selected region of the given image with the current foreground color.
(image-stroke-selection! image)
MediaScheme GIMP Procedure. Traces the edge of the selected region of the given image with the current brush and foreground color.

Additional Image Procedures

(image-airbrush-line! image pressure col1 row1 col2 row2)
MediaScheme GIMP Procedure. Draw a line in image from (col1,row1) to (col2,row2). Uses the airbrush and foreground color. The pressure should be between 0 and 100 (inclusive).
(image-copy-paste-block! source source-col source-row target target-col target-row width height)
MediaScheme GIMP Procedure. Copy a width-by-height region from source to target. The (col,row) pairs specify the top-left corner of the region in each image.
(image-refresh-display! image)
MediaScheme GIMP Procedure. Refreshes the display of the given image. (While context-update-displays! should update displays, it doesn't always work. This procedure forces an update. And it still doesn't always work. Doing a new call to image-show seems to refresh all copies of the image.)

Accessibility statement. Check accessibility with WAVE.

Copyright © Charlie Curtsinger, Janet Davis, Titus Klinge, Samuel A. Rebelsky, and Jerod Weinman. Selected materials are copyright by John David Stone or Henry Walker and are used with permission.

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