• Wiki
• Download
• Manual
• Eggs
• API
• Tests
• Bugs

chicken-stb-image

This is a CHICKEN egg that wraps stb_image.h version 2.19 from Sean Barrett and friends. It works on CHICKEN 4 and 5.

API

[procedure] (read-image #!key channels)
[procedure] (load-image u8vector #!key channels)

Decodes an image into raw pixel data. read-image reads the image from from (current-input-port) while load-image gets this from the provided u8vector. The image type is detected by content, and may be: JPEG, PNG, TGA, BMP, PSD, GIF, HDR, PIC, PNM as explained in the heading comments of stb_image.h.

Both procedures return 4 values:

1. raw pixel data (as u8vector)
2. width
3. height
4. number of channels

You can force the number of channels with the channels keyword. If channels is #f or not given, the number of channels in the original image will be used.

The size of the pixel data blob is always (* width height channels) bytes. The first pixel is the top-left-most in the image. Each pixel is channel number of bytes long. The number of channels define the pixel color, interleaved as follows:

1. grey
2. grey, alpha
3. red, green, blue
4. red, green, blue, alpha

read-image may read beyond the image data, so the data in current-input-port should contain only one image.

[procedure] (read-image-info)
[procedure] (load-image-info blob)

Like read-image and load-image, but does not load pixel data and should be faster. Returns three values:

1. width
2. height
3. number of channels

Note that on 32-bit systems, blobs cannot be larger than 16M. This limits image sizes as pixel data is stored as blobs.

Examples

For quick testing, you can read PNGs from ImageMagick's convert:

$ convert -size 4x4 xc:blue -draw 'line 0,0 4,4' png:- | csi -R stb-image -p '(read-image)'
#u8(0 0 0     0 0 234   0 0 255   0 0 255
    0 0 234   0 0 0     0 0 234   0 0 255
    0 0 255   0 0 234   0 0 0     0 0 234
    0 0 255   0 0 255   0 0 234   0 0 0)
4
4
3

Which reveal the black line along the diagonal and informs that the image is 4x4 with 3-channels.

Remerber to open files in #:binary mode for things to work on Windows:

 (with-input-from-file "rose.png" read-image-info #:binary)

Known limitations

backwards seek not implemented

Some special-case images try to seek backwards in the internal API. This hasn't been implemented due to increased complexity: you may see a "backwards seek not implemented" error. If this is a show-stopper, contact the author.