Images

image.ss

This teachpack provides primitives for constructing and manipulating images. These functions create basic shapes. The mode can be either 'solid or "solid", meaning the shape is filled in, or 'outline or "outline", meaning the shape is hollow. Image colors can be either symbols (like 'blue), strings (like "blue"), or color structs (like (make-color 0 0 255)) -- see below for more information about color structs.

rectangle : int int mode image-color -> image
to create a rectangle using the given width, height, mode, and color

circle : int mode image-color -> image
to create a circle using the given radius, mode, and color

ellipse : int int mode image-color -> image
to create an ellipse using the given width, height, and color

triangle : int mode iamge-color -> image
to create an upward pointing equilateral triangle using the given edge size and color

line : number number image-color -> image
to create an image with a colored line from (0,0) to the point with the given coordinates

add-line : image number number number number image-color -> image
to add a line to an existing image, drawn between the two given points

text : string size image-color -> image
to create an image of the text in the given string, with the point size, and color specified by the last two arguments

These functions build complex images from the basic shapes. When two images are laid on top of each other, the are lined up at their pinhole. Most shapes have their pinholes in the middle. The exceptions are text and line which have their pinholes in the top-left corner.

overlay : image image image ... -> image
to add the pixels of the second image onto the first image, lining up the pinholes

overlay/xy : image int int image -> image
to add the pixels of the second image onto the first image. Instead of lining up on the pinhole, the second image's pinhole is lined up with an offset from the first image's pinhole. The two coordinates specify how far down and to the right the offset should be. The pinhole of the resulting image is the same place as the pinhole in the first image.

After an image has been overlaid on another, it is possible to recover the position of overlaid image, using the next two functions.

image-inside? : image image -> boolean
to determine whether the pixels of the second image appear in the first

Be careful when using this function with jpeg images. If you use an image-editing program to crop a jpeg image and then save it, image-inside? will not recognize the cropped image, due to jpeg's compression.

Use png images instead.

find-image : image image -> posn
to determine where the pixels of the second image appear in the first, with respect to the pinhole of the first image.

The shrink functions trim an image by eliminating extraneous pixels.

shrink-tl : image number number -> image
to shrink the image, starting from the top-left corner. The two numbers indicate how many pixels to save. The pinhole of the resulting image is in the middle of the image.

shrink-tr : image number number -> image
to shrink the image, starting from the top-right corner. The two numbers indicate how many pixels to save. The pinhole of the resulting image is in the middle of the image.

shrink-bl : image number number -> image
to shrink the image, starting from the bottom-left corner. The two numbers indicate how many pixels to save. The pinhole of the resulting image is in the middle of the image.

shrink-br : image number number -> image
to shrink the image, starting from the bottom-right corner. The two numbers indicate how many pixels to save. The pinhole of the resulting image is in the middle of the image.

shrink : image number number number number -> image
to shrink an image around its pinhole. The numbers are the pixels to save to left, above, to the right, and below the pinhole, respectively. The pixel directly on the pinhole is always saved.

These functions provide information about the image's size.

image-width : image -> number
to obtain an image's width in pixels

image-height : image -> number
to obtain an image's height in pixels

This functions provide information and manipulate an image's pinhole.

pinhole-x : image -> number
to determine the x coordinate of the pinhole, measuring from the left of the image

pinhole-y : image -> number
to determine the y coordinate of the pinhole, measuring down from the left of the image

move-pinhole : image number number -> image
to move the pinhole down and to the right (by the specified amounts) of its current location. Use negative numbers to move it up or to the left.

put-pinhole : image number number -> image
to put the pinhole in the location specified by the arguments, counting from the left and down from the top, respectively.

This function precisely specifies what a valid image color is.

image-color? : anything -> boolean
to determine if the input is a valid image color

The next functions separate an image into its consitiuent colors and combine pixels together to build an image.

image->color-list : image -> list-of-color
to convert an image to a list of colors

color-list->image : list-of-color int int int int -> image
to convert a list of colors to an image with the given width and height, and pinhole coordinates (the pinhole coordinates are with respect to the top-left of the image).

make-color : int int int -> color
to construct a color

color? : anything -> boolean
to determine if its input is a color

color-red : color -> int
to extract the red component of a color

color-green : color -> int
to extract the green component of a color

color-blue : color -> int
to extract the blue component of a color

Like the last group of functions, these functions separate an image into its consitiuent colors and combine pixels together to build an image, but these provide alpha-channel information as well. Alpha channels are a measure of transparency; 0 indicates fully opaque and 255 indicates fully transparent.

image->alpha-color-list : image -> list-of-alpha-color
to convert an image to a list of alpha colors

alpha-color-list->image : list-of-alpha-color int int int int -> image
to convert a list of alpha colors to an image with the given width and height, and pinhole coordinates (the pinhole coordinates are with respect to the top-left of the image).

make-alpha-color : int int int int -> color
to construct an alpha color

alpha-color? : anything -> boolean
to determine if its input is a color

alpha-color-alpha : color -> int
to extract the alpha value of a color

alpha-color-red : color -> int
to extract the red component of a color

alpha-color-green : color -> int
to extract the green component of a color

alpha-color-blue : color -> int
to extract the blue component of a color"