image 0.21.2

Imaging library written in Rust. Provides basic filters and decoders for the most common image formats.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320

use byteorder::{LittleEndian, WriteBytesExt};
use std::io::{self, Write};

use color;

const BITMAPFILEHEADER_SIZE: u32 = 14;
const BITMAPINFOHEADER_SIZE: u32 = 40;
const BITMAPV4HEADER_SIZE: u32 = 108;

/// The representation of a BMP encoder.
pub struct BMPEncoder<'a, W: 'a> {
    writer: &'a mut W,
}

impl<'a, W: Write + 'a> BMPEncoder<'a, W> {
    /// Create a new encoder that writes its output to ```w```.
    pub fn new(w: &'a mut W) -> Self {
        BMPEncoder { writer: w }
    }

    /// Encodes the image ```image```
    /// that has dimensions ```width``` and ```height```
    /// and ```ColorType``` ```c```.
    pub fn encode(
        &mut self,
        image: &[u8],
        width: u32,
        height: u32,
        c: color::ColorType,
    ) -> io::Result<()> {
        let bmp_header_size = BITMAPFILEHEADER_SIZE;

        let (dib_header_size, written_pixel_size, palette_color_count) = try!(get_pixel_info(c));
        let row_pad_size = (4 - (width * written_pixel_size) % 4) % 4; // each row must be padded to a multiple of 4 bytes

        let image_size = width * height * written_pixel_size + (height * row_pad_size);
        let palette_size = palette_color_count * 4; // all palette colors are BGRA
        let file_size = bmp_header_size + dib_header_size + palette_size + image_size;

        // write BMP header
        try!(self.writer.write_u8(b'B'));
        try!(self.writer.write_u8(b'M'));
        try!(self.writer.write_u32::<LittleEndian>(file_size)); // file size
        try!(self.writer.write_u16::<LittleEndian>(0)); // reserved 1
        try!(self.writer.write_u16::<LittleEndian>(0)); // reserved 2
        try!(
            self.writer
                .write_u32::<LittleEndian>(bmp_header_size + dib_header_size + palette_size)
        ); // image data offset

        // write DIB header
        try!(self.writer.write_u32::<LittleEndian>(dib_header_size));
        try!(self.writer.write_i32::<LittleEndian>(width as i32));
        try!(self.writer.write_i32::<LittleEndian>(height as i32));
        try!(self.writer.write_u16::<LittleEndian>(1)); // color planes
        try!(
            self.writer
                .write_u16::<LittleEndian>((written_pixel_size * 8) as u16)
        ); // bits per pixel
        if dib_header_size >= BITMAPV4HEADER_SIZE {
            // Assume BGRA32
            try!(self.writer.write_u32::<LittleEndian>(3)); // compression method - bitfields
        } else {
            try!(self.writer.write_u32::<LittleEndian>(0)); // compression method - no compression
        }
        try!(self.writer.write_u32::<LittleEndian>(image_size));
        try!(self.writer.write_i32::<LittleEndian>(0)); // horizontal ppm
        try!(self.writer.write_i32::<LittleEndian>(0)); // vertical ppm
        try!(self.writer.write_u32::<LittleEndian>(palette_color_count));
        try!(self.writer.write_u32::<LittleEndian>(0)); // all colors are important
        if dib_header_size >= BITMAPV4HEADER_SIZE {
            // Assume BGRA32
            try!(self.writer.write_u32::<LittleEndian>(0xff << 16)); // red mask
            try!(self.writer.write_u32::<LittleEndian>(0xff << 8)); // green mask
            try!(self.writer.write_u32::<LittleEndian>(0xff << 0)); // blue mask
            try!(self.writer.write_u32::<LittleEndian>(0xff << 24)); // alpha mask
            try!(self.writer.write_u32::<LittleEndian>(0x73524742)); // colorspace - sRGB
            // endpoints (3x3) and gamma (3)
            for _ in 0..12 {
                try!(self.writer.write_u32::<LittleEndian>(0));
            }
        }

        // write image data
        match c {
            color::ColorType::RGB(8) => {
                try!(self.encode_rgb(image, width, height, row_pad_size, 3))
            }
            color::ColorType::RGBA(8) => {
                try!(self.encode_rgba(image, width, height, row_pad_size, 4))
            }
            color::ColorType::Gray(8) => {
                try!(self.encode_gray(image, width, height, row_pad_size, 1))
            }
            color::ColorType::GrayA(8) => {
                try!(self.encode_gray(image, width, height, row_pad_size, 2))
            }
            _ => {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidInput,
                    &get_unsupported_error_message(c)[..],
                ))
            }
        }

        Ok(())
    }

    fn encode_rgb(
        &mut self,
        image: &[u8],
        width: u32,
        height: u32,
        row_pad_size: u32,
        bytes_per_pixel: u32,
    ) -> io::Result<()> {
        let x_stride = bytes_per_pixel;
        let y_stride = width * x_stride;
        for row in 0..height {
            // from the bottom up
            let row_start = (height - row - 1) * y_stride;
            for col in 0..width {
                let pixel_start = (row_start + (col * x_stride)) as usize;
                let r = image[pixel_start];
                let g = image[pixel_start + 1];
                let b = image[pixel_start + 2];
                // written as BGR
                try!(self.writer.write_u8(b));
                try!(self.writer.write_u8(g));
                try!(self.writer.write_u8(r));
                // alpha is never written as it's not widely supported
            }

            try!(self.write_row_pad(row_pad_size));
        }

        Ok(())
    }

    fn encode_rgba(
        &mut self,
        image: &[u8],
        width: u32,
        height: u32,
        row_pad_size: u32,
        bytes_per_pixel: u32,
    ) -> io::Result<()> {
        let x_stride = bytes_per_pixel;
        let y_stride = width * x_stride;
        for row in 0..height {
            // from the bottom up
            let row_start = (height - row - 1) * y_stride;
            for col in 0..width {
                let pixel_start = (row_start + (col * x_stride)) as usize;
                let r = image[pixel_start];
                let g = image[pixel_start + 1];
                let b = image[pixel_start + 2];
                let a = image[pixel_start + 3];
                // written as BGRA
                try!(self.writer.write_u8(b));
                try!(self.writer.write_u8(g));
                try!(self.writer.write_u8(r));
                try!(self.writer.write_u8(a));
            }

            try!(self.write_row_pad(row_pad_size));
        }

        Ok(())
    }

    fn encode_gray(
        &mut self,
        image: &[u8],
        width: u32,
        height: u32,
        row_pad_size: u32,
        bytes_per_pixel: u32,
    ) -> io::Result<()> {
        // write grayscale palette
        for val in 0..256 {
            // each color is written as BGRA, where A is always 0 and since only grayscale is being written, B = G = R = index
            let val = val as u8;
            try!(self.writer.write_u8(val));
            try!(self.writer.write_u8(val));
            try!(self.writer.write_u8(val));
            try!(self.writer.write_u8(0));
        }

        // write image data
        let x_stride = bytes_per_pixel;
        let y_stride = width * x_stride;
        for row in 0..height {
            // from the bottom up
            let row_start = (height - row - 1) * y_stride;
            for col in 0..width {
                let pixel_start = (row_start + (col * x_stride)) as usize;
                // color value is equal to the palette index
                try!(self.writer.write_u8(image[pixel_start]));
                // alpha is never written as it's not widely supported
            }

            try!(self.write_row_pad(row_pad_size));
        }

        Ok(())
    }

    fn write_row_pad(&mut self, row_pad_size: u32) -> io::Result<()> {
        for _ in 0..row_pad_size {
            try!(self.writer.write_u8(0));
        }

        Ok(())
    }
}

fn get_unsupported_error_message(c: color::ColorType) -> String {
    format!(
        "Unsupported color type {:?}.  Supported types: RGB(8), RGBA(8), Gray(8), GrayA(8).",
        c
    )
}

/// Returns a tuple representing: (dib header size, written pixel size, palette color count).
fn get_pixel_info(c: color::ColorType) -> io::Result<(u32, u32, u32)> {
    let sizes = match c {
        color::ColorType::RGB(8) => (BITMAPINFOHEADER_SIZE, 3, 0),
        color::ColorType::RGBA(8) => (BITMAPV4HEADER_SIZE, 4, 0),
        color::ColorType::Gray(8) => (BITMAPINFOHEADER_SIZE, 1, 256),
        color::ColorType::GrayA(8) => (BITMAPINFOHEADER_SIZE, 1, 256),
        _ => {
            return Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                &get_unsupported_error_message(c)[..],
            ))
        }
    };

    Ok(sizes)
}

#[cfg(test)]
mod tests {
    use super::super::BMPDecoder;
    use super::BMPEncoder;
    use color::ColorType;
    use image::ImageDecoder;
    use std::io::Cursor;

    fn round_trip_image(image: &[u8], width: u32, height: u32, c: ColorType) -> Vec<u8> {
        let mut encoded_data = Vec::new();
        {
            let mut encoder = BMPEncoder::new(&mut encoded_data);
            encoder
                .encode(&image, width, height, c)
                .expect("could not encode image");
        }

        let decoder = BMPDecoder::new(Cursor::new(&encoded_data)).expect("failed to decode");
        decoder.read_image().expect("failed to decode")
    }

    #[test]
    fn round_trip_single_pixel_rgb() {
        let image = [255u8, 0, 0]; // single red pixel
        let decoded = round_trip_image(&image, 1, 1, ColorType::RGB(8));
        assert_eq!(3, decoded.len());
        assert_eq!(255, decoded[0]);
        assert_eq!(0, decoded[1]);
        assert_eq!(0, decoded[2]);
    }

    #[test]
    fn round_trip_single_pixel_rgba() {
        let image = [1, 2, 3, 4];
        let decoded = round_trip_image(&image, 1, 1, ColorType::RGBA(8));
        assert_eq!(&decoded[..], &image[..]);
    }

    #[test]
    fn round_trip_3px_rgb() {
        let image = [0u8; 3 * 3 * 3]; // 3x3 pixels, 3 bytes per pixel
        let _decoded = round_trip_image(&image, 3, 3, ColorType::RGB(8));
    }

    #[test]
    fn round_trip_gray() {
        let image = [0u8, 1, 2]; // 3 pixels
        let decoded = round_trip_image(&image, 3, 1, ColorType::Gray(8));
        // should be read back as 3 RGB pixels
        assert_eq!(9, decoded.len());
        assert_eq!(0, decoded[0]);
        assert_eq!(0, decoded[1]);
        assert_eq!(0, decoded[2]);
        assert_eq!(1, decoded[3]);
        assert_eq!(1, decoded[4]);
        assert_eq!(1, decoded[5]);
        assert_eq!(2, decoded[6]);
        assert_eq!(2, decoded[7]);
        assert_eq!(2, decoded[8]);
    }

    #[test]
    fn round_trip_graya() {
        let image = [0u8, 0, 1, 0, 2, 0]; // 3 pixels, each with an alpha channel
        let decoded = round_trip_image(&image, 1, 3, ColorType::GrayA(8));
        // should be read back as 3 RGB pixels
        assert_eq!(9, decoded.len());
        assert_eq!(0, decoded[0]);
        assert_eq!(0, decoded[1]);
        assert_eq!(0, decoded[2]);
        assert_eq!(1, decoded[3]);
        assert_eq!(1, decoded[4]);
        assert_eq!(1, decoded[5]);
        assert_eq!(2, decoded[6]);
        assert_eq!(2, decoded[7]);
        assert_eq!(2, decoded[8]);
    }
}