## TOC »

- image-processing
- Color spaces
- Images
- Creating images
- Basic image information
- Logical and morphological operations
- PNM movies
- Image operations
- Image pairs
- Thresholding
- Colour Threshold
- Histogram Equalization
- Adaptive Thresholding
- Histogram
- Rendering Line Segments
- Points and bounding boxes
- Quantization
- Ellipses
- Resizing
- Connected Components
- Chains
- Conjuring
- Distance Transform
- Buffers
- Misc
- Stacking
- Angles
- Display
- License

## image-processing

This page is maintained in the package's github repository.

This is a Chicken Scheme egg with various image processing utilities.

Note that a few of these functions call ImageMagick.

### Color spaces

`*max-red*`constant`*max-green*`constant`*max-blue*`constant`*max-grey*`constant`*max-hue*`constant`*max-saturation*`constant`*max-value*`constantThese are exposed in case we want to switch to 16-bit grayscale or colors.

`rgb->hsv``rgb`procedure`hsv->rgb``hsv`procedure`rgb->cd``rgb`procedure`rgb->cmyk``rgb`procedure`rgb->uv-hsv``c`procedureVarious color space conversions. Colors are vectors of values.

`rgb->xyz``c`procedure`xyz->rgb``c`procedure`xyz->l*ab``c`procedure`l*ab->xyz``c`procedure`rgb->l*ab``c`procedure`l*ab->rgb``c`procedureConvert to l*ab. Colors are vectors of values. This is space in which Euclidean distance is similar to human perceputal distance. These implement a 2 degree observer and the D65 illuminant.

`rgb->html``c`procedureNot really a color space conversion, covert an rgb color to an HTML color

*#rrggbb*.

### Images

`define-structure``pbm``raw?``bitmap`record`define-structure``pgm``raw?``maxval``grey`record`define-structure``ppm``raw?``maxval``red``green``blue`record`pnm?``m`procedureThree image formats are supported. PBMs are binary images, PGMs are greyscale and PPMs are tri-plane (nominally RGB) images. All planes are stored as scheme matrices. Together all of these formats are called PNM. This is a standard format that many tools (such browser and ImageMagick) can read and write. PNMs can be serialized as either raw packed binaries or ascii text files. Note that we are unable to read or write raw PBMs.

`image-ref``i``p`procedureIndex into an PNM image or into a matrix. This is like indexing into a matrix except that the arguments are reversed. A

*matrix-ref*takes the row and then the column, image-ref takes a point which is an (x,y) coordinate.

`pbm-ascii``pbm`procedureEnsure that the PBM image is in ascii. We are unable to read or write raw PBMs.

`pnm-copy``pnm`procedureThe resulting image will not share any data with the original.

### Creating images

`read-pnm``pathname`procedureRead a PNM. We determine the kind of image (PBM, PGM, PPM see above) from the file header.

`write-pnm``pnm``pathname`procedureWrite a PNM. If don't provide an extension an appropriate one will be appended to your pathname.

`pbm-constant``width``height``bit`procedure`pgm-constant``width``height``grey`procedure`ppm-constant``width``height``red``green``blue`procedureCreate constant images.

`pbm-left-vertical-stripe``width``height``left`procedureCreate a black vertical stripe on a white image.

`crop-image``pnm``x``y``width``height`procedureCrop an image and return a new image of the given size.

`pnm->ppm``pnm`procedure`pnm->pgm``pnm`procedureConvert any image format to a color or greyscale image

`pbm->pgm``pbm`procedure`pgm->ppm``pgm`procedure`pbm->ppm``pbm`procedure`ppm->pgm``ppm`procedureVarious image conversions.

`pgm->pbm``pgm``threshold`procedure`ppm->pbm``ppm``threshold`procedureConvert a color or greyscale image to a binary image with the provided threshold.

### Basic image information

`pnm-width``pnm`procedure`pnm-height``pnm`procedureBasic image information.

`ppm-hue``ppm`procedure`ppm-saturation``ppm`procedure`ppm-value``ppm`procedureCreates a greyscale image representing one of the HSV channels from a color image.

`ppm-mean``image``colour-transform`procedure`ppm-covariance``image``colour-transform`procedure`pgm-mean``image`procedure`pgm-variance``image`procedureCompute the mean or covariance of an image. These take an optional colour transform.

### Logical and morphological operations

`pbm-and``pbm1``pbm2`procedure`pbm-or``pbm1``pbm2`procedure`pbm-not``pbm`procedure`pbm-xor``pbm1``pbm2`procedureBasic logical operations on binary images.

`pgm-absolute-difference``pgm1``pgm2`procedureCompute the difference between two greyscale images.

`empty-pnm?``pnm`procedureIs this image empty?

`pbm-skeletonize``pbm`procedure`pbm-bloat``pbm``n`procedureBloat or skeletonize a binary image.

`pbm-flood``pbm``point`procedureFloor fill a binary image.

### PNM movies

`pnm-movie-frame-pathname``pathname``i`procedure`pnm-movie-length``pathname`procedure`read-pnm-movie``pathname`procedure`write-pnm-movie``pnm-movie``pathname`procedureA PNM movie is a sequence of PNMs on disk.

### Image operations

`overlay-pbm-on-pnm``pbm``pnm`procedureThe white pixels in the pbm become white in the resulting image.

`pnm-black-window``pnm``upper-left``lower-right`procedure`pnm-white-window``pnm``upper-left``lower-right`procedureDraw white or black windows on an image.

`pbm-ppm-and``pbm``ppm`procedure`pgm-and-pbm``pgm``pbm`procedureBlack pixels in the PBM become black pixels in the result.

`pnm-shift``pnm``delta`procedureShift an image down and rightward by the give number of pixels.

`pgm-smooth``pgm``sigma`procedureSmooth a greyscale image with the given variance.

`pbm-proximity-clusterer``pbm``threshold`procedureCluster white pixels in the binary image with the given distance threshold.

`pnm-rotate``pnm`procedure`pnm-flip``pnm`procedureRotate (transpose) an image or flip (mirror) an image.

`ppm-burn``base``mask``colour`procedureBurn the ppm with the given mask and color.

### Image pairs

`normal-flow-magnitude``pgm1``pgm2``epsilon``sigma``sensitivity`procedure`threshold-normal-flow-magnitude``pgm1``pgm2``epsilon``sigma``threshold`procedureCompute normalized flow between two pairs of greyscale images.

### Thresholding

`flatten-ppm``ppm``colour-transform`procedureReturns a single matrix from a tri-plane PPM. This maps colour-transform over the image.

`binary-threshold``pgm``threshold`procedureThreshold a greyscale image.

`find-threshold-otsu``pgm`procedure`binary-threshold-optimal``pgm`procedureOtsu's Method to find an optional threshold and apply it.

`find-threshold-means``pgm`procedure`binary-threshold-means``pgm`procedureMethod of Successive Means to find an optimal threshold and apply it.

### Colour Threshold

`sample-image``ppm``colour-tx``window-centre``window-size`procedureMap colour-tx over an region of a color image.

`binary-threshold-colour``ppm``colour-tx``point``threshold`procedureBinary threshold a colour image by sampling a region around the given point and thresholding all values that are within the given distance threshold of the mean color of that region.

`colour-threshold``ppm``colour-tx``mu``isigma``threshold`procedureBinary threshold a colour image with the given mean and variance. The mahalanobis-distance between each pixel and the given mean and variance will be computed and compared to the threshold.

### Histogram Equalization

`histogram-equalise``pgm`procedureEqualize a greyscale image.

### Adaptive Thresholding

`make-integral-matrix``matrix`procedureGiven a matrix compute an integral matrix which can provide the mean value of a rectangular region in O(1).

`compute-integral-matrix-mu``integral-matrix``x``y``w`procedure`compute-integral-matrix-sigma``squared-integral-matrix``mu``x``y``w`procedureThis computes the mean and variance of a square of size w in the given integral matrix.

`compute-adaptive-threshold``integral-matrix``squared-integral-matrix``x``y``w`procedureCompute an adaptive threshold on the given integral matrix.

`adaptive-threshold``pgm``winsize`procedureCompute an adaptive threshold for a greyscale image with a given window size.

`slide-window``m``f``size`procedureMap f over a matrix passing it square submatrices of the given size. At the edges f is passed

*#f*.

`count-pixels``a`procedureCount number of true values in a matrix.

`ppm->label-closest``ppm``mu1``sigma1``mu2``sigma2``#!optional``colour-transform`procedureCreate a binary image from a color image where points are either white or black depending on which is closer to the given means and variances.

### Histogram

`find-histogram``pixmap``maxval`procedure`histogram-mean``histogram``i`procedure`histogram-variance``histogram``mu``i`procedure`normalised-histogram``histogram``val`procedure`weighted-histogram``histogram`procedure`cumulative-histogram``histogram`procedure`find-between-class-variances``omegas``mus``mu-total`procedureCompute histograms from a matrix.

### Rendering Line Segments

`midpoint``l`procedureCompute the midpoint of a line segment.

`orientation``v`procedureCompute the orientation of a vector.

`line-segment-orientation``l`procedureCompute the orientation of a line segment.

`line-segment->points``l`procedure`line-segments->points``ls`procedure`points->line-segments``ps`procedureConvert between points and line semgents.

### Points and bounding boxes

`points->pbm-of-size``points``height``width`procedureTake the list of points and create a binay image of the given size where those points are white.

`points-bounding-box``points`procedureComputing a bounding box for a set of points.

`bounding-box-size``bb`procedureCompute the size of a bounding box

`points->points-bounding-box``points``bb`procedureRecompute the coordinates of the given points relative to the top-left corner of the bounding box.

`points->bounding-box-points``points`procedureConvert points to a list of points on the bounding box of those points.

`normalize-to-bounding-box``ps`procedure`normalize-to-other-bounding-box``points``ps`procedure`points->target-bounding-box``points``target-bb`procedure`points->other-target-bounding-box``points``ps``target-bb`procedureNormalize the cooredinates of these points to their bounding box. Or to the bounding box of the given points.

`bounding-box-bloat``bb``p`procedureBloat a bounding box.

`bounding-box-crop``bb``image`procedureCrop a bounding box out of an image.

`pbm->points``pbm`procedure`points->pbm``points``height``width`procedureConvert a binary image to a set of points or vice versa.

### Quantization

`quantize-coordinate``x`procedure`quantize-point``p`procedure`quantize-points``ps`procedure`quantize-line-segment``l`procedure`quantize-line-segments``ls`procedureQuantize coordinates, points or line segments.

### Ellipses

`define-structure``ellipse``x0``y0``t0``a``b`procedure`ellipse-center``ellipse`procedure`ellipse-area``ellipse`procedure`ellipse-eccentricity``ellipse`procedureDefine and compute basic properties of ellipses.

`radial-distance``theta``phi`procedureThe radial distance between two angles.

`point-on-ellipse?``p``ellipse``tolerance`procedureCompute if a point is on an ellipse.

`line-segment->ellipse``l`procedurePlace an ellipse around a line segment

`ellipse->points``e``#!optional`(`n``360`)procedureSample

*n*points on an ellipse.

### Resizing

`resize-image``w``h``i`procedureResize an image. This is quite slow as it writes the image out and calls imagemagick to resize it.

`subsample-pbm``pbm`procedureSubsample a pbm by a factor of 2.

`scale-ppm``ppm``scale`procedureScale a pbm by a factor of 2 or 4.

### Connected Components

`connected-component-filter``pbm``delta``threshold`procedureCompute connected components of a binary image with distance thershold

*delta*and size threshold*threshold*.x

`define-private-structure``vertex``pixels``vertex``edges`record`define-private-structure``edge``u``v`record`define-private-structure``graph``vertices``edges`recordThese are defined private for now as they need to be renamed.

`pbm->graph``pbm``delta`procedure`labeling->graph``labeling``delta`procedureConvert a binary image to a graph where pixels within

*delta*of each other are connected.

`dereference-vertex``u`procedure`connected-components``g`procedureCompute the connect components of a graph.

`vertices->pbm``vertices``height``width`procedure`graph->pbm``g``height``width`procedureConvert a graph or list of vertices to a pbm.

### Chains

`pbm->chains``pbm`procedureConvert a binary image to a list of chains, pixels that are connected to each other.

`chains->pbm``chains``height``width`procedureConvert a list of chains to a pbm.

`chain-filter``pbm``threshold`procedureFilters chains below a certain length.

`break-chain``chain``l`procedure`break-chains``chains``l`procedureBreak chains below a certain length.

### Conjuring

`conjure``pbms``delta``span``threshold1``threshold2`procedureFill in missing values in pairs of frames.

### Distance Transform

`distance-transform``pbm`procedure`closest-transform-ref``closest-transform``p`procedureCompute the Manhattan distance transform for a binary image and reference into that distance transform.

`euclidean-1d-dt``v`procedure`euclidean-2d-dt``m`procedure`euclidean-1d-dt-vals``v`procedure`euclidean-2d-dt-vals``m`procedureCompute a generalized squared-euclidean distance transform on the given vector or matrix. The

*-vals*version also returns a map of the closest points.

### Buffers

`define-structure``pnm-buffer``buffer``width``height``pixfmt``storage``type`recordA mechanism to store raw image pointers.

`pnm->pixfmt``p``p4?`procedure`pixfmt->stride``pixfmt`procedure`image-type->pixfmt``t``p4?`procedure`image-type->storage-size``t``p4?`procedure`pnm->image-type``p`procedure`pnm->storage``p`procedure`pixfmt->red``pixfmt`procedure`pixfmt->green``pixfmt`procedure`pixfmt->blue``pixfmt`procedure`pnm-buffer-size``p``p4?`procedure`pnm->pnm-buffer!``p``#!rest``p4?`procedure`pnm-fill-buffer!``p``b``pixfmt`procedure`free-pnm-buffer!``p`procedureMisc raw image buffer operations.

`imlib-image->pnm-buffer!``image`procedure`imlib-image->ppm``image`procedure`ppm->imlib-image``ppm`procedureConvert between PPMs and Imlib images. PGMs and PBMs must first be converted to PPMs because Imlib only handles RGB images.

`pnm-buffer->pnm``b`procedure`pnm-buffer->pbm``p`procedure`pnm-buffer->pgm``p`procedure`pnm-buffer->ppm``p`procedureConvert a raw image buffer to a scheme image.

`image->pnm-buffer!``image`procedureConvert any image to a raw image buffer.

### Misc

`ppm-absolute-difference``ppm1``ppm2`procedureCompute the absolute difference between two color images.

`set-ppm-pixel!``ppm``x``y``value`procedureSet a pixel in a color image to a given value (a 3-vector).

`pnm-pixel?``i``x``y`procedureIs this a valid position in the given image?

`map-ppm-values``ppm``f`procedureMap

*f*on each component of each pixel in the image.

### Stacking

`pbm-stack-vertical``pbm1``pbm2`procedure`pbm-stack-horizontal``pbm1``pbm2`procedure`ppm-stack-vertical``ppm1``ppm2`procedureStack pbms.

`ppm-stack-horizontal``ppm1``ppm2`procedureStack ppms.

### Angles

`degrees->radians``angle`procedure`radians->degrees``angle`procedure`normalize-rotation``rotation`procedure`rotation+``x``y`procedure`rotation-``x``y`procedure`angle-separation``x``y`procedure`mean-angle``angles`procedureMisc operation on angles.

`rotation-matrix-2d``theta`procedureProduce the 2D rotation matrix for the given angle.

### Display

`show``i`procedureDisplay an image. This invokes feh.

### License

Written by the [[Center for the Computational Study of Cognition, Control, and Perception|http://upplysingaoflun.ecn.purdue.edu/~qobi/cccp/]].

Maintainer: Andrei Barbu, andrei@0xab.com

Copyright 1993-1995 University of Toronto. All rights reserved. Copyright 1996 Technion. All rights reserved. Copyright 1996 and 1997 University of Vermont. All rights reserved. Copyright 1997-2001 NEC Research Institute, Inc. All rights reserved. Copyright 2002-2013 Purdue University. All rights reserved. This program is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this program. If not, see http://www.gnu.org/licenses.