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# R7RS-PNM
R7RS-PNM is a R7RS library for handling PNM (Portable Any Map) files,
providing functionality for reading and writing PNM files,as well as
accessing and modifying pixel data.
## Usage
### Import `(pnm)` library
```scheme
(import (pnm))
```
### Image
#### `(image? x) → boolean`
Returns `#t` if `x` is a valid image object; otherwise, it returns
`#f`.
#### `(image-type image) → 'pbm | 'pgm | 'ppm`
Returns the type of the given image.
- `pbm`: Portable Bit Map
- `pgm`: Portable Gray Map
- `ppm`: Portable Pixel Map
#### `(image-width image) → integer`
Returns the width of `image`.
#### `(image-height image) → integer`
Returns the height of `image`.
### PBM (Portable Bit Map)
#### `(make-pbm-image width height) → <image>`
Returns a new Portable Bit Map (PBM) image with the specified width
and height.
#### `(image-maxval pbm-image) → #t`
Returns the maximum value for pixel intensity in a PBM image, which is
always `#t` for PBM images, indicating binary values (black and
white).
#### `(image-ref pbm-image x y) → boolean`
Returns the value of the pixel at coordinates `(x, y)` in the
specified `image`. The return value is `#t` for a white pixel and `#f`
for a black pixel.
#### `(image-set! pbm-image x y b)`
Sets the pixel at coordinates `(x, y)` in the specified `image` to
the boolean value `b`. If `b` is `#t`, the pixel is set to white; if
`#f`, it is set to black.
### PGM (Portable PGM Map)
#### `(make-pgm-image width height [maxval]) → <image>`
Creates a new Portable Gray Map (PGM) image with the specified width
and height. The optional `maxval` parameter defines the maximum pixel
intensity, defaulting to 255 if not provided.
#### `(image-maxval pgm-image) → integer`
Returns the maximum pixel intensity value for the specified PGM image.
#### `(image-ref pgm-image x y) → integer`
Returns the gray value of the pixel at coordinates `(x, y)` in the
specified PGM image. The value is an integer between 0 and `maxval`.
#### `(image-set! pgm-image x y v)`
Sets the pixel at coordinates `(x, y)` in the specified PGM image to
the given integer value `v`, which must be between 0 and `maxval`.
### PPM (Portable PPM Map)
#### `(make-ppm-image width height [maxval]) → <image>`
Creates a new Portable Pixel Map (PPM) image with the specified width
and height. The optional `maxval` parameter defines the maximum color
intensity, defaulting to 255 if not provided.
#### `(image-maxval ppm-image) → integer`
Returns the maximum color intensity value for the specified PPM image.
#### `(image-ref ppm-image x y) → (values integer integer integer)`
Returns the RGB values of the pixel at coordinates `(x, y)` in the
specified PPM image as three integers, representing the red, green,
and blue components, respectively.
### `(image-set! ppm-image x y r g b)`
Sets the pixel at coordinates `(x, y)` in the specified PPM image to
the given RGB values `r`, `g`, and `b`, which must be integers between
0 and `maxval`.
### Reading
#### `(image-read port) → <image>`
Reads a PNM image from the specified input `port` and returns the
corresponding image object (PBM, PGM, or PPM).
### `(pnm-parse-error? exn) → boolean`
Returns `#t` if the exception `exn` is a parse error that occurred
during the execution of the `image-read` procedure; otherwise, it
returns `#f`.
### Writing
### `(image-write image port)`
Writes the specified `image` (PBM, PGM, or PPM) to the given output
`port`.
### Downloading Code with Git
```bash
git clone https://git.tojo.tokyo/r7rs-pnm.git
```
## License
This library is released under the LGPLv3+ License.
See the COPYING and COPYING.LESSER files for more details.
## Copyright
Copyright (c) 2024 Masaya Tojo <masaya@tojo.tokyo>
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