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
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
use scoped_threadpool::Pool;
use num_traits::cast::NumCast;
use num_traits::identities::Zero;
use std::mem;
#[cfg(test)]
use std::borrow::Cow;
use std::error::Error;
use std::io::{self, BufRead, Cursor, Seek};
use std::iter::Iterator;
use std::path::Path;
use Primitive;

use color::{ColorType, Rgb};
use image::{self, ImageDecoder, ImageDecoderExt, ImageError, ImageResult, Progress};

/// Adapter to conform to ```ImageDecoder``` trait
#[derive(Debug)]
pub struct HDRAdapter<R: BufRead> {
    inner: Option<HDRDecoder<R>>,
    data: Option<Vec<u8>>,
    meta: HDRMetadata,
}

impl<R: BufRead> HDRAdapter<R> {
    /// Creates adapter
    pub fn new(r: R) -> ImageResult<HDRAdapter<R>> {
        let decoder = try!(HDRDecoder::new(r));
        let meta = decoder.metadata();
        Ok(HDRAdapter {
            inner: Some(decoder),
            data: None,
            meta,
        })
    }

    /// Allows reading old Radiance HDR images
    pub fn new_nonstrict(r: R) -> ImageResult<HDRAdapter<R>> {
        let decoder = try!(HDRDecoder::with_strictness(r, false));
        let meta = decoder.metadata();
        Ok(HDRAdapter {
            inner: Some(decoder),
            data: None,
            meta,
        })
    }

    /// Read the actual data of the image, and store it in Self::data.
    fn read_image_data(&mut self) -> ImageResult<()> {
        match self.inner.take() {
            Some(decoder) => {
                let img: Vec<Rgb<u8>> = decoder.read_image_ldr()?;

                let len = img.len() * mem::size_of::<Rgb<u8>>(); // length in bytes
                let target = self.data.get_or_insert_with(|| Vec::with_capacity(len));
                target.clear();

                for Rgb { data } in img {
                    target.extend_from_slice(&data);
                }

                Ok(())
            }
            None => Err(ImageError::ImageEnd),
        }
    }

}

impl<R: BufRead> ImageDecoder for HDRAdapter<R> {
    type Reader = Cursor<Vec<u8>>;

    fn dimensions(&self) -> (u64, u64) {
        (self.meta.width as u64, self.meta.height as u64)
    }

    fn colortype(&self) -> ColorType {
        ColorType::RGB(8)
    }

    fn into_reader(self) -> ImageResult<Self::Reader> {
        Ok(Cursor::new(self.read_image()?))
    }

    fn read_image(mut self) -> ImageResult<Vec<u8>> {
        if let Some(data) = self.data {
            return Ok(data);
        }

        self.read_image_data()?;
        Ok(self.data.unwrap())
    }
}

impl<R: BufRead + Seek> ImageDecoderExt for HDRAdapter<R> {
    fn read_rect_with_progress<F: Fn(Progress)>(
        &mut self,
        x: u64,
        y: u64,
        width: u64,
        height: u64,
        buf: &mut [u8],
        progress_callback: F,
    ) -> ImageResult<()> {
        if self.data.is_none() {
            self.read_image_data()?;
        }

        image::load_rect(x, y, width, height, buf, progress_callback, self, |_, _| unreachable!(),
                         |s, buf| {
                             buf.copy_from_slice(&*s.data.as_ref().unwrap());
                             Ok(buf.len())
                         })
    }
}

/// Radiance HDR file signature
pub const SIGNATURE: &[u8] = b"#?RADIANCE";
const SIGNATURE_LENGTH: usize = 10;

/// An Radiance HDR decoder
#[derive(Debug)]
pub struct HDRDecoder<R> {
    r: R,
    width: u32,
    height: u32,
    meta: HDRMetadata,
}

/// Refer to [wikipedia](https://en.wikipedia.org/wiki/RGBE_image_format)
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct RGBE8Pixel {
    /// Color components
    pub c: [u8; 3],
    /// Exponent
    pub e: u8,
}

/// Creates ```RGBE8Pixel``` from components
pub fn rgbe8(r: u8, g: u8, b: u8, e: u8) -> RGBE8Pixel {
    RGBE8Pixel { c: [r, g, b], e }
}

impl RGBE8Pixel {
    /// Converts ```RGBE8Pixel``` into ```Rgb<f32>``` linearly
    #[inline]
    pub fn to_hdr(self) -> Rgb<f32> {
        if self.e == 0 {
            Rgb([0.0, 0.0, 0.0])
        } else {
            //            let exp = f32::ldexp(1., self.e as isize - (128 + 8)); // unstable
            let exp = f32::exp2(<f32 as From<_>>::from(self.e) - (128.0 + 8.0));
            Rgb([
                exp * <f32 as From<_>>::from(self.c[0]),
                exp * <f32 as From<_>>::from(self.c[1]),
                exp * <f32 as From<_>>::from(self.c[2]),
            ])
        }
    }

    /// Converts ```RGBE8Pixel``` into ```Rgb<T>``` with scale=1 and gamma=2.2
    ///
    /// color_ldr = (color_hdr*scale)<sup>gamma</sup>
    ///
    /// # Panic
    ///
    /// Panics when ```T::max_value()``` cannot be represented as f32.
    #[inline]
    pub fn to_ldr<T: Primitive + Zero>(self) -> Rgb<T> {
        self.to_ldr_scale_gamma(1.0, 2.2)
    }

    /// Converts RGBE8Pixel into Rgb<T> using provided scale and gamma
    ///
    /// color_ldr = (color_hdr*scale)<sup>gamma</sup>
    ///
    /// # Panic
    ///
    /// Panics when T::max_value() cannot be represented as f32.
    /// Panics when scale or gamma is NaN
    #[inline]
    pub fn to_ldr_scale_gamma<T: Primitive + Zero>(self, scale: f32, gamma: f32) -> Rgb<T> {
        let Rgb { data } = self.to_hdr();
        let (r, g, b) = (data[0], data[1], data[2]);
        #[inline]
        fn sg<T: Primitive + Zero>(v: f32, scale: f32, gamma: f32) -> T {
            let t_max = T::max_value();
            // Disassembly shows that t_max_f32 is compiled into constant
            let t_max_f32: f32 = NumCast::from(t_max)
                .expect("to_ldr_scale_gamma: maximum value of type is not representable as f32");
            let fv = f32::powf(v * scale, gamma) * t_max_f32 + 0.5;
            if fv < 0.0 {
                T::zero()
            } else if fv > t_max_f32 {
                t_max
            } else {
                NumCast::from(fv)
                    .expect("to_ldr_scale_gamma: cannot convert f32 to target type. NaN?")
            }
        }
        Rgb([
            sg(r, scale, gamma),
            sg(g, scale, gamma),
            sg(b, scale, gamma),
        ])
    }
}

impl<R: BufRead> HDRDecoder<R> {
    /// Reads Radiance HDR image header from stream ```r```
    /// if the header is valid, creates HDRDecoder
    /// strict mode is enabled
    pub fn new(reader: R) -> ImageResult<HDRDecoder<R>> {
        HDRDecoder::with_strictness(reader, true)
    }

    /// Reads Radiance HDR image header from stream ```reader```,
    /// if the header is valid, creates ```HDRDecoder```.
    ///
    /// strict enables strict mode
    ///
    /// Warning! Reading wrong file in non-strict mode
    ///   could consume file size worth of memory in the process.
    pub fn with_strictness(mut reader: R, strict: bool) -> ImageResult<HDRDecoder<R>> {
        let mut attributes = HDRMetadata::new();

        {
            // scope to make borrowck happy
            let r = &mut reader;
            if strict {
                let mut signature = [0; SIGNATURE_LENGTH];
                try!(r.read_exact(&mut signature));
                if signature != SIGNATURE {
                    return Err(ImageError::FormatError(
                        "Radiance HDR signature not found".to_string(),
                    ));
                } // no else
                  // skip signature line ending
                try!(read_line_u8(r));
            } else {
                // Old Radiance HDR files (*.pic) don't use signature
                // Let them be parsed in non-strict mode
            }
            // read header data until empty line
            loop {
                match try!(read_line_u8(r)) {
                    None => {
                        // EOF before end of header
                        return Err(ImageError::FormatError("EOF in header".into()));
                    }
                    Some(line) => {
                        if line.is_empty() {
                            // end of header
                            break;
                        } else if line[0] == b'#' {
                            // line[0] will not panic, line.len() == 0 is false here
                            // skip comments
                            continue;
                        } // no else
                          // process attribute line
                        let line = String::from_utf8_lossy(&line[..]);
                        try!(attributes.update_header_info(&line, strict));
                    } // <= Some(line)
                } // match read_line_u8()
            } // loop
        } // scope to end borrow of reader
          // parse dimensions
        let (width, height) = match try!(read_line_u8(&mut reader)) {
            None => {
                // EOF instead of image dimensions
                return Err(ImageError::FormatError("EOF in dimensions line".into()));
            }
            Some(dimensions) => {
                let dimensions = String::from_utf8_lossy(&dimensions[..]);
                try!(parse_dimensions_line(&dimensions, strict))
            }
        };

        Ok(HDRDecoder {
            r: reader,

            width,
            height,
            meta: HDRMetadata {
                width,
                height,
                ..attributes
            },
        })
    } // end with_strictness

    /// Returns file metadata. Refer to ```HDRMetadata``` for details.
    pub fn metadata(&self) -> HDRMetadata {
        self.meta.clone()
    }

    /// Consumes decoder and returns a vector of RGBE8 pixels
    pub fn read_image_native(mut self) -> ImageResult<Vec<RGBE8Pixel>> {
        // Don't read anything if image is empty
        if self.width == 0 || self.height == 0 {
            return Ok(vec![]);
        }
        // expression self.width > 0 && self.height > 0 is true from now to the end of this method
        let pixel_count = self.width as usize * self.height as usize;
        let mut ret = vec![Default::default(); pixel_count];
        for chunk in ret.chunks_mut(self.width as usize) {
            try!(read_scanline(&mut self.r, chunk));
        }
        Ok(ret)
    }

    /// Consumes decoder and returns a vector of transformed pixels
    pub fn read_image_transform<T: Send, F: Send + Sync + Fn(RGBE8Pixel) -> T>(
        mut self,
        f: F,
    ) -> ImageResult<Vec<T>> {
        // Don't read anything if image is empty
        if self.width == 0 || self.height == 0 {
            return Ok(vec![]);
        }
        // expression self.width > 0 && self.height > 0 is true from now to the end of this method
        // scanline buffer
        let uszwidth = self.width as usize;

        let pixel_count = self.width as usize * self.height as usize;
        let mut ret = Vec::with_capacity(pixel_count);
        unsafe {
            // RGBE8Pixel doesn't implement Drop, so it's Ok to drop half-initialized ret
            ret.set_len(pixel_count);
        } // ret contains uninitialized data, so now it's my responsibility to return fully initialized ret

        {
            let chunks_iter = ret.chunks_mut(uszwidth);
            let mut pool = Pool::new(8); //

            try!(pool.scoped(|scope| {
                for chunk in chunks_iter {
                    let mut buf = Vec::<RGBE8Pixel>::with_capacity(uszwidth);
                    unsafe {
                        buf.set_len(uszwidth);
                    }
                    try!(read_scanline(&mut self.r, &mut buf[..]));
                    let f = &f;
                    scope.execute(move || {
                        for (dst, &pix) in chunk.iter_mut().zip(buf.iter()) {
                            *dst = f(pix);
                        }
                    });
                }
                Ok(())
            }) as Result<(), ImageError>);
        }

        Ok(ret)
    }

    /// Consumes decoder and returns a vector of Rgb<u8> pixels.
    /// scale = 1, gamma = 2.2
    pub fn read_image_ldr(self) -> ImageResult<Vec<Rgb<u8>>> {
        self.read_image_transform(|pix| pix.to_ldr())
    }

    /// Consumes decoder and returns a vector of Rgb<f32> pixels.
    ///
    pub fn read_image_hdr(self) -> ImageResult<Vec<Rgb<f32>>> {
        self.read_image_transform(|pix| pix.to_hdr())
    }
}

impl<R: BufRead> IntoIterator for HDRDecoder<R> {
    type Item = ImageResult<RGBE8Pixel>;
    type IntoIter = HDRImageDecoderIterator<R>;

    fn into_iter(self) -> Self::IntoIter {
        HDRImageDecoderIterator {
            r: self.r,
            scanline_cnt: self.height as usize,
            buf: vec![Default::default(); self.width as usize],
            col: 0,
            scanline: 0,
            trouble: true, // make first call to `next()` read scanline
            error_encountered: false,
        }
    }
}

/// Scanline buffered pixel by pixel iterator
pub struct HDRImageDecoderIterator<R: BufRead> {
    r: R,
    scanline_cnt: usize,
    buf: Vec<RGBE8Pixel>, // scanline buffer
    col: usize,           // current position in scanline
    scanline: usize,      // current scanline
    trouble: bool,        // optimization, true indicates that we need to check something
    error_encountered: bool,
}

impl<R: BufRead> HDRImageDecoderIterator<R> {
    // Advances counter to the next pixel
    #[inline]
    fn advance(&mut self) {
        self.col += 1;
        if self.col == self.buf.len() {
            self.col = 0;
            self.scanline += 1;
            self.trouble = true;
        }
    }
}

impl<R: BufRead> Iterator for HDRImageDecoderIterator<R> {
    type Item = ImageResult<RGBE8Pixel>;

    fn next(&mut self) -> Option<Self::Item> {
        if !self.trouble {
            let ret = self.buf[self.col];
            self.advance();
            Some(Ok(ret))
        } else {
            // some condition is pending
            if self.buf.is_empty() || self.scanline == self.scanline_cnt {
                // No more pixels
                return None;
            } // no else
            if self.error_encountered {
                self.advance();
                // Error was encountered. Keep producing errors.
                // ImageError can't implement Clone, so just dump some error
                return Some(Err(ImageError::ImageEnd));
            } // no else
            if self.col == 0 {
                // fill scanline buffer
                match read_scanline(&mut self.r, &mut self.buf[..]) {
                    Ok(_) => {
                        // no action required
                    }
                    Err(err) => {
                        self.advance();
                        self.error_encountered = true;
                        self.trouble = true;
                        return Some(Err(err));
                    }
                }
            } // no else
            self.trouble = false;
            let ret = self.buf[0];
            self.advance();
            Some(Ok(ret))
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let total_cnt = self.buf.len() * self.scanline_cnt;
        let cur_cnt = self.buf.len() * self.scanline + self.col;
        let remaining = total_cnt - cur_cnt;
        (remaining, Some(remaining))
    }
}

impl<R: BufRead> ExactSizeIterator for HDRImageDecoderIterator<R> {}

// Precondition: buf.len() > 0
fn read_scanline<R: BufRead>(r: &mut R, buf: &mut [RGBE8Pixel]) -> ImageResult<()> {
    assert!(!buf.is_empty());
    let width = buf.len();
    // first 4 bytes in scanline allow to determine compression method
    let fb = try!(read_rgbe(r));
    if fb.c[0] == 2 && fb.c[1] == 2 && fb.c[2] < 128 {
        // denormalized pixel value (2,2,<128,_) indicates new per component RLE method
        // decode_component guarantees that offset is within 0 .. width
        // therefore we can skip bounds checking here, but we will not
        try!(decode_component(r, width, |offset, value| buf[offset].c[0] = value));
        try!(decode_component(r, width, |offset, value| buf[offset].c[1] = value));
        try!(decode_component(r, width, |offset, value| buf[offset].c[2] = value));
        try!(decode_component(r, width, |offset, value| buf[offset].e = value));
    } else {
        // old RLE method (it was considered old around 1991, should it be here?)
        try!(decode_old_rle(r, fb, buf));
    }
    Ok(())
}

#[inline(always)]
fn read_byte<R: BufRead>(r: &mut R) -> io::Result<u8> {
    let mut buf = [0u8];
    try!(r.read_exact(&mut buf[..]));
    Ok(buf[0])
}

// Guarantees that first parameter of set_component will be within pos .. pos+width
#[inline]
fn decode_component<R: BufRead, S: FnMut(usize, u8)>(
    r: &mut R,
    width: usize,
    mut set_component: S,
) -> ImageResult<()> {
    let mut buf = [0; 128];
    let mut pos = 0;
    while pos < width {
        // increment position by a number of decompressed values
        pos += {
            let rl = try!(read_byte(r));
            if rl <= 128 {
                // sanity check
                if pos + rl as usize > width {
                    return Err(ImageError::FormatError(
                        "Wrong length of decoded scanline".into(),
                    ));
                }
                // read values
                try!(r.read_exact(&mut buf[0..rl as usize]));
                for (offset, &value) in buf[0..rl as usize].iter().enumerate() {
                    set_component(pos + offset, value);
                }
                rl as usize
            } else {
                // run
                let rl = rl - 128;
                // sanity check
                if pos + rl as usize > width {
                    return Err(ImageError::FormatError(
                        "Wrong length of decoded scanline".into(),
                    ));
                }
                // fill with same value
                let value = try!(read_byte(r));
                for offset in 0..rl as usize {
                    set_component(pos + offset, value);
                }
                rl as usize
            }
        };
    }
    if pos != width {
        return Err(ImageError::FormatError(
            "Wrong length of decoded scanline".into(),
        ));
    }
    Ok(())
}

// Decodes scanline, places it into buf
// Precondition: buf.len() > 0
// fb - first 4 bytes of scanline
fn decode_old_rle<R: BufRead>(
    r: &mut R,
    fb: RGBE8Pixel,
    buf: &mut [RGBE8Pixel],
) -> ImageResult<()> {
    assert!(!buf.is_empty());
    let width = buf.len();
    // convenience function.
    // returns run length if pixel is a run length marker
    #[inline]
    fn rl_marker(pix: RGBE8Pixel) -> Option<usize> {
        if pix.c == [1, 1, 1] {
            Some(pix.e as usize)
        } else {
            None
        }
    }
    // first pixel in scanline should not be run length marker
    // it is error if it is
    if rl_marker(fb).is_some() {
        return Err(ImageError::FormatError(
            "First pixel of a scanline shouldn't be run length marker".into(),
        ));
    }
    buf[0] = fb; // set first pixel of scanline

    let mut x_off = 1; // current offset from beginning of a scanline
    let mut rl_mult = 1; // current run length multiplier
    let mut prev_pixel = fb;
    while x_off < width {
        let pix = try!(read_rgbe(r));
        // it's harder to forget to increase x_off if I write this this way.
        x_off += {
            if let Some(rl) = rl_marker(pix) {
                // rl_mult takes care of consecutive RL markers
                let rl = rl * rl_mult;
                rl_mult *= 256;
                if x_off + rl <= width {
                    // do run
                    for b in &mut buf[x_off..x_off + rl] {
                        *b = prev_pixel;
                    }
                } else {
                    return Err(ImageError::FormatError(
                        "Wrong length of decoded scanline".into(),
                    ));
                };
                rl // value to increase x_off by
            } else {
                rl_mult = 1; // chain of consecutive RL markers is broken
                prev_pixel = pix;
                buf[x_off] = pix;
                1 // value to increase x_off by
            }
        };
    }
    if x_off != width {
        return Err(ImageError::FormatError(
            "Wrong length of decoded scanline".into(),
        ));
    }
    Ok(())
}

fn read_rgbe<R: BufRead>(r: &mut R) -> io::Result<RGBE8Pixel> {
    let mut buf = [0u8; 4];
    try!(r.read_exact(&mut buf[..]));
    Ok(RGBE8Pixel {c: [buf[0], buf[1], buf[2]], e: buf[3] })
}

/// Metadata for Radiance HDR image
#[derive(Debug, Clone)]
pub struct HDRMetadata {
    /// Width of decoded image. It could be either scanline length,
    /// or scanline count, depending on image orientation.
    pub width: u32,
    /// Height of decoded image. It depends on orientation too.
    pub height: u32,
    /// Orientation matrix. For standard orientation it is ((1,0),(0,1)) - left to right, top to bottom.
    /// First pair tells how resulting pixel coordinates change along a scanline.
    /// Second pair tells how they change from one scanline to the next.
    pub orientation: ((i8, i8), (i8, i8)),
    /// Divide color values by exposure to get to get physical radiance in
    /// watts/steradian/m<sup>2</sup>
    ///
    /// Image may not contain physical data, even if this field is set.
    pub exposure: Option<f32>,
    /// Divide color values by corresponding tuple member (r, g, b) to get to get physical radiance
    /// in watts/steradian/m<sup>2</sup>
    ///
    /// Image may not contain physical data, even if this field is set.
    pub color_correction: Option<(f32, f32, f32)>,
    /// Pixel height divided by pixel width
    pub pixel_aspect_ratio: Option<f32>,
    /// All lines contained in image header are put here. Ordering of lines is preserved.
    /// Lines in the form "key=value" are represented as ("key", "value").
    /// All other lines are ("", "line")
    pub custom_attributes: Vec<(String, String)>,
}

impl HDRMetadata {
    fn new() -> HDRMetadata {
        HDRMetadata {
            width: 0,
            height: 0,
            orientation: ((1, 0), (0, 1)),
            exposure: None,
            color_correction: None,
            pixel_aspect_ratio: None,
            custom_attributes: vec![],
        }
    }

    // Updates header info, in strict mode returns error for malformed lines (no '=' separator)
    // unknown attributes are skipped
    fn update_header_info(&mut self, line: &str, strict: bool) -> ImageResult<()> {
        // split line at first '='
        // old Radiance HDR files (*.pic) feature tabs in key, so                vvv trim
        let maybe_key_value = split_at_first(line, "=").map(|(key, value)| (key.trim(), value));
        // save all header lines in custom_attributes
        match maybe_key_value {
            Some((key, val)) => self.custom_attributes
                .push((key.to_owned(), val.to_owned())),
            None => self.custom_attributes.push(("".into(), line.to_owned())),
        }
        // parse known attributes
        match maybe_key_value {
            Some(("FORMAT", val)) => {
                if val.trim() != "32-bit_rle_rgbe" {
                    // XYZE isn't supported yet
                    return Err(ImageError::UnsupportedError(limit_string_len(val, 20)));
                }
            }
            Some(("EXPOSURE", val)) => {
                match val.trim().parse::<f32>() {
                    Ok(v) => {
                        self.exposure = Some(self.exposure.unwrap_or(1.0) * v); // all encountered exposure values should be multiplied
                    }
                    Err(parse_error) => {
                        if strict {
                            return Err(ImageError::FormatError(format!(
                                "Cannot parse EXPOSURE value: {}",
                                parse_error.description()
                            )));
                        } // no else, skip this line in non-strict mode
                    }
                };
            }
            Some(("PIXASPECT", val)) => {
                match val.trim().parse::<f32>() {
                    Ok(v) => {
                        self.pixel_aspect_ratio = Some(self.pixel_aspect_ratio.unwrap_or(1.0) * v); // all encountered exposure values should be multiplied
                    }
                    Err(parse_error) => {
                        if strict {
                            return Err(ImageError::FormatError(format!(
                                "Cannot parse PIXASPECT value: {}",
                                parse_error.description()
                            )));
                        } // no else, skip this line in non-strict mode
                    }
                };
            }
            Some(("COLORCORR", val)) => {
                let mut rgbcorr = [1.0, 1.0, 1.0];
                match parse_space_separated_f32(val, &mut rgbcorr, "COLORCORR") {
                    Ok(extra_numbers) => {
                        if strict && extra_numbers {
                            return Err(ImageError::FormatError(
                                "Extra numbers in COLORCORR".into(),
                            ));
                        } // no else, just ignore extra numbers
                        let (rc, gc, bc) = self.color_correction.unwrap_or((1.0, 1.0, 1.0));
                        self.color_correction =
                            Some((rc * rgbcorr[0], gc * rgbcorr[1], bc * rgbcorr[2]));
                    }
                    Err(err) => {
                        if strict {
                            return Err(err);
                        } // no else, skip malformed line in non-strict mode
                    }
                }
            }
            None => {
                // old Radiance HDR files (*.pic) contain commands in a header
                // just skip them
            }
            _ => {
                // skip unknown attribute
            }
        } // match attributes
        Ok(())
    }
}

fn parse_space_separated_f32(line: &str, vals: &mut [f32], name: &str) -> ImageResult<bool> {
    let mut nums = line.split_whitespace();
    for val in vals.iter_mut() {
        if let Some(num) = nums.next() {
            match num.parse::<f32>() {
                Ok(v) => *val = v,
                Err(err) => {
                    return Err(ImageError::FormatError(format!(
                        "f32 parse error in {}: {}",
                        name,
                        err.description()
                    )));
                }
            }
        } else {
            // not enough numbers in line
            return Err(ImageError::FormatError(format!(
                "Not enough numbers in {}",
                name
            )));
        }
    }
    Ok(nums.next().is_some())
}

// Parses dimension line "-Y height +X width"
// returns (width, height) or error
fn parse_dimensions_line(line: &str, strict: bool) -> ImageResult<(u32, u32)> {
    let mut dim_parts = line.split_whitespace();
    let err = "Malformed dimensions line";
    let c1_tag = try!(
        dim_parts
            .next()
            .ok_or_else(|| ImageError::FormatError(err.into()))
    );
    let c1_str = try!(
        dim_parts
            .next()
            .ok_or_else(|| ImageError::FormatError(err.into()))
    );
    let c2_tag = try!(
        dim_parts
            .next()
            .ok_or_else(|| ImageError::FormatError(err.into()))
    );
    let c2_str = try!(
        dim_parts
            .next()
            .ok_or_else(|| ImageError::FormatError(err.into()))
    );
    if strict && dim_parts.next().is_some() {
        // extra data in dimensions line
        return Err(ImageError::FormatError(err.into()));
    } // no else
      // dimensions line is in the form "-Y 10 +X 20"
      // There are 8 possible orientations: +Y +X, +X -Y and so on
    match (c1_tag, c2_tag) {
        ("-Y", "+X") => {
            // Common orientation (left-right, top-down)
            // c1_str is height, c2_str is width
            let height = try!(c1_str.parse::<u32>().into_image_error(err));
            let width = try!(c2_str.parse::<u32>().into_image_error(err));
            Ok((width, height))
        }
        _ => Err(ImageError::FormatError(format!(
            "Unsupported orientation {} {}",
            limit_string_len(c1_tag, 4),
            limit_string_len(c2_tag, 4)
        ))),
    } // final expression. Returns value
}

trait IntoImageError<T> {
    fn into_image_error(self, description: &str) -> ImageResult<T>;
}

impl<T> IntoImageError<T> for ::std::result::Result<T, ::std::num::ParseFloatError> {
    fn into_image_error(self, description: &str) -> ImageResult<T> {
        self.map_err(|err| {
            ImageError::FormatError(format!("{} {}", description, err.description()))
        })
    }
}

impl<T> IntoImageError<T> for ::std::result::Result<T, ::std::num::ParseIntError> {
    fn into_image_error(self, description: &str) -> ImageResult<T> {
        self.map_err(|err| {
            ImageError::FormatError(format!("{} {}", description, err.description()))
        })
    }
}

// Returns string with no more than len+3 characters
fn limit_string_len(s: &str, len: usize) -> String {
    let s_char_len = s.chars().count();
    if s_char_len > len {
        s.chars().take(len).chain("...".chars()).collect()
    } else {
        s.into()
    }
}

// Splits string into (before separator, after separator) tuple
// or None if separator isn't found
fn split_at_first<'a>(s: &'a str, separator: &str) -> Option<(&'a str, &'a str)> {
    match s.find(separator) {
        None | Some(0) => None,
        Some(p) if p >= s.len() - separator.len() => None,
        Some(p) => Some((&s[..p], &s[(p + separator.len())..])),
    }
}

#[test]
fn split_at_first_test() {
    assert_eq!(split_at_first(&Cow::Owned("".into()), "="), None);
    assert_eq!(split_at_first(&Cow::Owned("=".into()), "="), None);
    assert_eq!(split_at_first(&Cow::Owned("= ".into()), "="), None);
    assert_eq!(
        split_at_first(&Cow::Owned(" = ".into()), "="),
        Some((" ", " "))
    );
    assert_eq!(
        split_at_first(&Cow::Owned("EXPOSURE= ".into()), "="),
        Some(("EXPOSURE", " "))
    );
    assert_eq!(
        split_at_first(&Cow::Owned("EXPOSURE= =".into()), "="),
        Some(("EXPOSURE", " ="))
    );
    assert_eq!(
        split_at_first(&Cow::Owned("EXPOSURE== =".into()), "=="),
        Some(("EXPOSURE", " ="))
    );
    assert_eq!(split_at_first(&Cow::Owned("EXPOSURE".into()), ""), None);
}

// Reads input until b"\n" or EOF
// Returns vector of read bytes NOT including end of line characters
//   or return None to indicate end of file
fn read_line_u8<R: BufRead>(r: &mut R) -> ::std::io::Result<Option<Vec<u8>>> {
    let mut ret = Vec::with_capacity(16);
    match r.read_until(b'\n', &mut ret) {
        Ok(0) => Ok(None),
        Ok(_) => {
            if let Some(&b'\n') = ret[..].last() {
                let _ = ret.pop();
            }
            Ok(Some(ret))
        }
        Err(err) => Err(err),
    }
}

#[test]
fn read_line_u8_test() {
    let buf: Vec<_> = (&b"One\nTwo\nThree\nFour\n\n\n"[..]).into();
    let input = &mut ::std::io::Cursor::new(buf);
    assert_eq!(&read_line_u8(input).unwrap().unwrap()[..], &b"One"[..]);
    assert_eq!(&read_line_u8(input).unwrap().unwrap()[..], &b"Two"[..]);
    assert_eq!(&read_line_u8(input).unwrap().unwrap()[..], &b"Three"[..]);
    assert_eq!(&read_line_u8(input).unwrap().unwrap()[..], &b"Four"[..]);
    assert_eq!(&read_line_u8(input).unwrap().unwrap()[..], &b""[..]);
    assert_eq!(&read_line_u8(input).unwrap().unwrap()[..], &b""[..]);
    assert_eq!(read_line_u8(input).unwrap(), None);
}

/// Helper function for reading raw 3-channel f32 images
pub fn read_raw_file<P: AsRef<Path>>(path: P) -> ::std::io::Result<Vec<Rgb<f32>>> {
    use byteorder::{LittleEndian as LE, ReadBytesExt};
    use std::fs::File;
    use std::io::BufReader;

    let mut r = BufReader::new(try!(File::open(path)));
    let w = try!(r.read_u32::<LE>()) as usize;
    let h = try!(r.read_u32::<LE>()) as usize;
    let c = try!(r.read_u32::<LE>()) as usize;
    assert_eq!(c, 3);
    let cnt = w * h;
    let mut ret = Vec::with_capacity(cnt);
    for _ in 0..cnt {
        let cr = try!(r.read_f32::<LE>());
        let cg = try!(r.read_f32::<LE>());
        let cb = try!(r.read_f32::<LE>());
        ret.push(Rgb([cr, cg, cb]));
    }
    Ok(ret)
}