This is an egg for CHICKEN 4, the unsupported old release. You're almost certainly looking for the CHICKEN 5 version of this egg, if it exists.
If it does not exist, there may be equivalent functionality provided by another egg; have a look at the egg index. Otherwise, please consider porting this egg to the current version of CHICKEN.
- read-image #!key channelsprocedure
- load-image u8vector #!key channelsprocedure
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:
- raw pixel data (as u8vector)
- 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:
- grey, alpha
- red, green, blue
- red, green, blue, alpha
read-image may read beyond the image data, so the data in current-input-port should contain only one image.
- load-image-info blobprocedure
- 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.
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.
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.