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
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
use std::ops::{Index, IndexMut};

use num_traits::{NumCast, ToPrimitive, Zero};

use crate::traits::{Enlargeable, Pixel, Primitive};

/// An enumeration over supported color types and bit depths
#[derive(Copy, PartialEq, Eq, Debug, Clone, Hash)]
#[non_exhaustive]
pub enum ColorType {
    /// Pixel is 8-bit luminance
    L8,
    /// Pixel is 8-bit luminance with an alpha channel
    La8,
    /// Pixel contains 8-bit R, G and B channels
    Rgb8,
    /// Pixel is 8-bit RGB with an alpha channel
    Rgba8,

    /// Pixel is 16-bit luminance
    L16,
    /// Pixel is 16-bit luminance with an alpha channel
    La16,
    /// Pixel is 16-bit RGB
    Rgb16,
    /// Pixel is 16-bit RGBA
    Rgba16,

    /// Pixel is 32-bit float RGB
    Rgb32F,
    /// Pixel is 32-bit float RGBA
    Rgba32F,
}

impl ColorType {
    /// Returns the number of bytes contained in a pixel of `ColorType` ```c```
    pub fn bytes_per_pixel(self) -> u8 {
        match self {
            ColorType::L8 => 1,
            ColorType::L16 | ColorType::La8 => 2,
            ColorType::Rgb8 => 3,
            ColorType::Rgba8 | ColorType::La16 => 4,
            ColorType::Rgb16 => 6,
            ColorType::Rgba16 => 8,
            ColorType::Rgb32F => 3 * 4,
            ColorType::Rgba32F => 4 * 4,
        }
    }

    /// Returns if there is an alpha channel.
    pub fn has_alpha(self) -> bool {
        use ColorType::*;
        match self {
            L8 | L16 | Rgb8 | Rgb16 | Rgb32F => false,
            La8 | Rgba8 | La16 | Rgba16 | Rgba32F => true,
        }
    }

    /// Returns false if the color scheme is grayscale, true otherwise.
    pub fn has_color(self) -> bool {
        use ColorType::*;
        match self {
            L8 | L16 | La8 | La16 => false,
            Rgb8 | Rgb16 | Rgba8 | Rgba16 | Rgb32F | Rgba32F => true,
        }
    }

    /// Returns the number of bits contained in a pixel of `ColorType` ```c``` (which will always be
    /// a multiple of 8).
    pub fn bits_per_pixel(self) -> u16 {
        <u16 as From<u8>>::from(self.bytes_per_pixel()) * 8
    }

    /// Returns the number of color channels that make up this pixel
    pub fn channel_count(self) -> u8 {
        let e: ExtendedColorType = self.into();
        e.channel_count()
    }
}

/// An enumeration of color types encountered in image formats.
///
/// This is not exhaustive over all existing image formats but should be granular enough to allow
/// round tripping of decoding and encoding as much as possible. The variants will be extended as
/// necessary to enable this.
///
/// Another purpose is to advise users of a rough estimate of the accuracy and effort of the
/// decoding from and encoding to such an image format.
#[derive(Copy, PartialEq, Eq, Debug, Clone, Hash)]
#[non_exhaustive]
pub enum ExtendedColorType {
    /// Pixel is 8-bit alpha
    A8,
    /// Pixel is 1-bit luminance
    L1,
    /// Pixel is 1-bit luminance with an alpha channel
    La1,
    /// Pixel contains 1-bit R, G and B channels
    Rgb1,
    /// Pixel is 1-bit RGB with an alpha channel
    Rgba1,
    /// Pixel is 2-bit luminance
    L2,
    /// Pixel is 2-bit luminance with an alpha channel
    La2,
    /// Pixel contains 2-bit R, G and B channels
    Rgb2,
    /// Pixel is 2-bit RGB with an alpha channel
    Rgba2,
    /// Pixel is 4-bit luminance
    L4,
    /// Pixel is 4-bit luminance with an alpha channel
    La4,
    /// Pixel contains 4-bit R, G and B channels
    Rgb4,
    /// Pixel is 4-bit RGB with an alpha channel
    Rgba4,
    /// Pixel is 8-bit luminance
    L8,
    /// Pixel is 8-bit luminance with an alpha channel
    La8,
    /// Pixel contains 8-bit R, G and B channels
    Rgb8,
    /// Pixel is 8-bit RGB with an alpha channel
    Rgba8,
    /// Pixel is 16-bit luminance
    L16,
    /// Pixel is 16-bit luminance with an alpha channel
    La16,
    /// Pixel contains 16-bit R, G and B channels
    Rgb16,
    /// Pixel is 16-bit RGB with an alpha channel
    Rgba16,
    /// Pixel contains 8-bit B, G and R channels
    Bgr8,
    /// Pixel is 8-bit BGR with an alpha channel
    Bgra8,

    // TODO f16 types?
    /// Pixel is 32-bit float RGB
    Rgb32F,
    /// Pixel is 32-bit float RGBA
    Rgba32F,

    /// Pixel is of unknown color type with the specified bits per pixel. This can apply to pixels
    /// which are associated with an external palette. In that case, the pixel value is an index
    /// into the palette.
    Unknown(u8),
}

impl ExtendedColorType {
    /// Get the number of channels for colors of this type.
    ///
    /// Note that the `Unknown` variant returns a value of `1` since pixels can only be treated as
    /// an opaque datum by the library.
    pub fn channel_count(self) -> u8 {
        match self {
            ExtendedColorType::A8
            | ExtendedColorType::L1
            | ExtendedColorType::L2
            | ExtendedColorType::L4
            | ExtendedColorType::L8
            | ExtendedColorType::L16
            | ExtendedColorType::Unknown(_) => 1,
            ExtendedColorType::La1
            | ExtendedColorType::La2
            | ExtendedColorType::La4
            | ExtendedColorType::La8
            | ExtendedColorType::La16 => 2,
            ExtendedColorType::Rgb1
            | ExtendedColorType::Rgb2
            | ExtendedColorType::Rgb4
            | ExtendedColorType::Rgb8
            | ExtendedColorType::Rgb16
            | ExtendedColorType::Rgb32F
            | ExtendedColorType::Bgr8 => 3,
            ExtendedColorType::Rgba1
            | ExtendedColorType::Rgba2
            | ExtendedColorType::Rgba4
            | ExtendedColorType::Rgba8
            | ExtendedColorType::Rgba16
            | ExtendedColorType::Rgba32F
            | ExtendedColorType::Bgra8 => 4,
        }
    }
}
impl From<ColorType> for ExtendedColorType {
    fn from(c: ColorType) -> Self {
        match c {
            ColorType::L8 => ExtendedColorType::L8,
            ColorType::La8 => ExtendedColorType::La8,
            ColorType::Rgb8 => ExtendedColorType::Rgb8,
            ColorType::Rgba8 => ExtendedColorType::Rgba8,
            ColorType::L16 => ExtendedColorType::L16,
            ColorType::La16 => ExtendedColorType::La16,
            ColorType::Rgb16 => ExtendedColorType::Rgb16,
            ColorType::Rgba16 => ExtendedColorType::Rgba16,
            ColorType::Rgb32F => ExtendedColorType::Rgb32F,
            ColorType::Rgba32F => ExtendedColorType::Rgba32F,
        }
    }
}

macro_rules! define_colors {
    {$(
        $(#[$doc:meta])*
        pub struct $ident:ident<T: $($bound:ident)*>([T; $channels:expr, $alphas:expr])
            = $interpretation:literal;
    )*} => {

$( // START Structure definitions

$(#[$doc])*
#[derive(PartialEq, Eq, Clone, Debug, Copy, Hash)]
#[repr(C)]
#[allow(missing_docs)]
pub struct $ident<T> (pub [T; $channels]);

impl<T: $($bound+)*> Pixel for $ident<T> {
    type Subpixel = T;

    const CHANNEL_COUNT: u8 = $channels;

    #[inline(always)]
    fn channels(&self) -> &[T] {
        &self.0
    }

    #[inline(always)]
    fn channels_mut(&mut self) -> &mut [T] {
        &mut self.0
    }

    const COLOR_MODEL: &'static str = $interpretation;

    fn channels4(&self) -> (T, T, T, T) {
        const CHANNELS: usize = $channels;
        let mut channels = [T::DEFAULT_MAX_VALUE; 4];
        channels[0..CHANNELS].copy_from_slice(&self.0);
        (channels[0], channels[1], channels[2], channels[3])
    }

    fn from_channels(a: T, b: T, c: T, d: T,) -> $ident<T> {
        const CHANNELS: usize = $channels;
        *<$ident<T> as Pixel>::from_slice(&[a, b, c, d][..CHANNELS])
    }

    fn from_slice(slice: &[T]) -> &$ident<T> {
        assert_eq!(slice.len(), $channels);
        unsafe { &*(slice.as_ptr() as *const $ident<T>) }
    }
    fn from_slice_mut(slice: &mut [T]) -> &mut $ident<T> {
        assert_eq!(slice.len(), $channels);
        unsafe { &mut *(slice.as_mut_ptr() as *mut $ident<T>) }
    }

    fn to_rgb(&self) -> Rgb<T> {
        let mut pix = Rgb([Zero::zero(), Zero::zero(), Zero::zero()]);
        pix.from_color(self);
        pix
    }

    fn to_rgba(&self) -> Rgba<T> {
        let mut pix = Rgba([Zero::zero(), Zero::zero(), Zero::zero(), Zero::zero()]);
        pix.from_color(self);
        pix
    }

    fn to_luma(&self) -> Luma<T> {
        let mut pix = Luma([Zero::zero()]);
        pix.from_color(self);
        pix
    }

    fn to_luma_alpha(&self) -> LumaA<T> {
        let mut pix = LumaA([Zero::zero(), Zero::zero()]);
        pix.from_color(self);
        pix
    }

    fn map<F>(& self, f: F) -> $ident<T> where F: FnMut(T) -> T {
        let mut this = (*self).clone();
        this.apply(f);
        this
    }

    fn apply<F>(&mut self, mut f: F) where F: FnMut(T) -> T {
        for v in &mut self.0 {
            *v = f(*v)
        }
    }

    fn map_with_alpha<F, G>(&self, f: F, g: G) -> $ident<T> where F: FnMut(T) -> T, G: FnMut(T) -> T {
        let mut this = (*self).clone();
        this.apply_with_alpha(f, g);
        this
    }

    fn apply_with_alpha<F, G>(&mut self, mut f: F, mut g: G) where F: FnMut(T) -> T, G: FnMut(T) -> T {
        const ALPHA: usize = $channels - $alphas;
        for v in self.0[..ALPHA].iter_mut() {
            *v = f(*v)
        }
        // The branch of this match is `const`. This way ensures that no subexpression fails the
        // `const_err` lint (the expression `self.0[ALPHA]` would).
        if let Some(v) = self.0.get_mut(ALPHA) {
            *v = g(*v)
        }
    }

    fn map2<F>(&self, other: &Self, f: F) -> $ident<T> where F: FnMut(T, T) -> T {
        let mut this = (*self).clone();
        this.apply2(other, f);
        this
    }

    fn apply2<F>(&mut self, other: &$ident<T>, mut f: F) where F: FnMut(T, T) -> T {
        for (a, &b) in self.0.iter_mut().zip(other.0.iter()) {
            *a = f(*a, b)
        }
    }

    fn invert(&mut self) {
        Invert::invert(self)
    }

    fn blend(&mut self, other: &$ident<T>) {
        Blend::blend(self, other)
    }
}

impl<T> Index<usize> for $ident<T> {
    type Output = T;
    #[inline(always)]
    fn index(&self, _index: usize) -> &T {
        &self.0[_index]
    }
}

impl<T> IndexMut<usize> for $ident<T> {
    #[inline(always)]
    fn index_mut(&mut self, _index: usize) -> &mut T {
        &mut self.0[_index]
    }
}

impl<T> From<[T; $channels]> for $ident<T> {
    fn from(c: [T; $channels]) -> Self {
        Self(c)
    }
}

)* // END Structure definitions

    }
}

define_colors! {
    /// RGB colors.
    ///
    /// For the purpose of color conversion, as well as blending, the implementation of `Pixel`
    /// assumes an `sRGB` color space of its data.
    pub struct Rgb<T: Primitive Enlargeable>([T; 3, 0]) = "RGB";
    /// Grayscale colors.
    pub struct Luma<T: Primitive>([T; 1, 0]) = "Y";
    /// RGB colors + alpha channel
    pub struct Rgba<T: Primitive Enlargeable>([T; 4, 1]) = "RGBA";
    /// Grayscale colors + alpha channel
    pub struct LumaA<T: Primitive>([T; 2, 1]) = "YA";
}

/// Convert from one pixel component type to another. For example, convert from `u8` to `f32` pixel values.
pub trait FromPrimitive<Component> {
    /// Converts from any pixel component type to this type.
    fn from_primitive(component: Component) -> Self;
}

impl<T: Primitive> FromPrimitive<T> for T {
    fn from_primitive(sample: T) -> Self {
        sample
    }
}

// from f32:
// Note that in to-integer-conversion we are performing rounding but NumCast::from is implemented
// as truncate towards zero. We emulate rounding by adding a bias.

impl FromPrimitive<f32> for u8 {
    fn from_primitive(float: f32) -> Self {
        let inner = (float.clamp(0.0, 1.0) * u8::MAX as f32).round();
        NumCast::from(inner).unwrap()
    }
}

impl FromPrimitive<f32> for u16 {
    fn from_primitive(float: f32) -> Self {
        let inner = (float.clamp(0.0, 1.0) * u16::MAX as f32).round();
        NumCast::from(inner).unwrap()
    }
}

// from u16:

impl FromPrimitive<u16> for u8 {
    fn from_primitive(c16: u16) -> Self {
        fn from(c: impl Into<u32>) -> u32 {
            c.into()
        }
        // The input c is the numerator of `c / u16::MAX`.
        // Derive numerator of `num / u8::MAX`, with rounding.
        //
        // This method is based on the inverse (see FromPrimitive<u8> for u16) and was tested
        // exhaustively in Python. It's the same as the reference function:
        //  round(c * (2**8 - 1) / (2**16 - 1))
        NumCast::from((from(c16) + 128) / 257).unwrap()
    }
}

impl FromPrimitive<u16> for f32 {
    fn from_primitive(int: u16) -> Self {
        (int as f32 / u16::MAX as f32).clamp(0.0, 1.0)
    }
}

// from u8:

impl FromPrimitive<u8> for f32 {
    fn from_primitive(int: u8) -> Self {
        (int as f32 / u8::MAX as f32).clamp(0.0, 1.0)
    }
}

impl FromPrimitive<u8> for u16 {
    fn from_primitive(c8: u8) -> Self {
        let x = c8.to_u64().unwrap();
        NumCast::from((x << 8) | x).unwrap()
    }
}

/// Provides color conversions for the different pixel types.
pub trait FromColor<Other> {
    /// Changes `self` to represent `Other` in the color space of `Self`
    fn from_color(&mut self, _: &Other);
}

/// Copy-based conversions to target pixel types using `FromColor`.
// FIXME: this trait should be removed and replaced with real color space models
// rather than assuming sRGB.
pub(crate) trait IntoColor<Other> {
    /// Constructs a pixel of the target type and converts this pixel into it.
    fn into_color(&self) -> Other;
}

impl<O, S> IntoColor<O> for S
where
    O: Pixel + FromColor<S>,
{
    fn into_color(&self) -> O {
        // Note we cannot use Pixel::CHANNELS_COUNT here to directly construct
        // the pixel due to a current bug/limitation of consts.
        #[allow(deprecated)]
        let mut pix = O::from_channels(Zero::zero(), Zero::zero(), Zero::zero(), Zero::zero());
        pix.from_color(self);
        pix
    }
}

/// Coefficients to transform from sRGB to a CIE Y (luminance) value.
const SRGB_LUMA: [u32; 3] = [2126, 7152, 722];
const SRGB_LUMA_DIV: u32 = 10000;

#[inline]
fn rgb_to_luma<T: Primitive + Enlargeable>(rgb: &[T]) -> T {
    let l = <T::Larger as NumCast>::from(SRGB_LUMA[0]).unwrap() * rgb[0].to_larger()
        + <T::Larger as NumCast>::from(SRGB_LUMA[1]).unwrap() * rgb[1].to_larger()
        + <T::Larger as NumCast>::from(SRGB_LUMA[2]).unwrap() * rgb[2].to_larger();
    T::clamp_from(l / <T::Larger as NumCast>::from(SRGB_LUMA_DIV).unwrap())
}

// `FromColor` for Luma
impl<S: Primitive, T: Primitive> FromColor<Luma<S>> for Luma<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Luma<S>) {
        let own = self.channels_mut();
        let other = other.channels();
        own[0] = T::from_primitive(other[0]);
    }
}

impl<S: Primitive, T: Primitive> FromColor<LumaA<S>> for Luma<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &LumaA<S>) {
        self.channels_mut()[0] = T::from_primitive(other.channels()[0])
    }
}

impl<S: Primitive + Enlargeable, T: Primitive> FromColor<Rgb<S>> for Luma<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Rgb<S>) {
        let gray = self.channels_mut();
        let rgb = other.channels();
        gray[0] = T::from_primitive(rgb_to_luma(rgb));
    }
}

impl<S: Primitive + Enlargeable, T: Primitive> FromColor<Rgba<S>> for Luma<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Rgba<S>) {
        let gray = self.channels_mut();
        let rgb = other.channels();
        let l = rgb_to_luma(rgb);
        gray[0] = T::from_primitive(l);
    }
}

// `FromColor` for LumaA

impl<S: Primitive, T: Primitive> FromColor<LumaA<S>> for LumaA<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &LumaA<S>) {
        let own = self.channels_mut();
        let other = other.channels();
        own[0] = T::from_primitive(other[0]);
        own[1] = T::from_primitive(other[1]);
    }
}

impl<S: Primitive + Enlargeable, T: Primitive> FromColor<Rgb<S>> for LumaA<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Rgb<S>) {
        let gray_a = self.channels_mut();
        let rgb = other.channels();
        gray_a[0] = T::from_primitive(rgb_to_luma(rgb));
        gray_a[1] = T::DEFAULT_MAX_VALUE;
    }
}

impl<S: Primitive + Enlargeable, T: Primitive> FromColor<Rgba<S>> for LumaA<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Rgba<S>) {
        let gray_a = self.channels_mut();
        let rgba = other.channels();
        gray_a[0] = T::from_primitive(rgb_to_luma(rgba));
        gray_a[1] = T::from_primitive(rgba[3]);
    }
}

impl<S: Primitive, T: Primitive> FromColor<Luma<S>> for LumaA<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Luma<S>) {
        let gray_a = self.channels_mut();
        gray_a[0] = T::from_primitive(other.channels()[0]);
        gray_a[1] = T::DEFAULT_MAX_VALUE;
    }
}

// `FromColor` for RGBA

impl<S: Primitive, T: Primitive> FromColor<Rgba<S>> for Rgba<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Rgba<S>) {
        let own = &mut self.0;
        let other = &other.0;
        own[0] = T::from_primitive(other[0]);
        own[1] = T::from_primitive(other[1]);
        own[2] = T::from_primitive(other[2]);
        own[3] = T::from_primitive(other[3]);
    }
}

impl<S: Primitive, T: Primitive> FromColor<Rgb<S>> for Rgba<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Rgb<S>) {
        let rgba = &mut self.0;
        let rgb = &other.0;
        rgba[0] = T::from_primitive(rgb[0]);
        rgba[1] = T::from_primitive(rgb[1]);
        rgba[2] = T::from_primitive(rgb[2]);
        rgba[3] = T::DEFAULT_MAX_VALUE;
    }
}

impl<S: Primitive, T: Primitive> FromColor<LumaA<S>> for Rgba<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, gray: &LumaA<S>) {
        let rgba = &mut self.0;
        let gray = &gray.0;
        rgba[0] = T::from_primitive(gray[0]);
        rgba[1] = T::from_primitive(gray[0]);
        rgba[2] = T::from_primitive(gray[0]);
        rgba[3] = T::from_primitive(gray[1]);
    }
}

impl<S: Primitive, T: Primitive> FromColor<Luma<S>> for Rgba<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, gray: &Luma<S>) {
        let rgba = &mut self.0;
        let gray = gray.0[0];
        rgba[0] = T::from_primitive(gray);
        rgba[1] = T::from_primitive(gray);
        rgba[2] = T::from_primitive(gray);
        rgba[3] = T::DEFAULT_MAX_VALUE;
    }
}

// `FromColor` for RGB

impl<S: Primitive, T: Primitive> FromColor<Rgb<S>> for Rgb<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Rgb<S>) {
        let own = &mut self.0;
        let other = &other.0;
        own[0] = T::from_primitive(other[0]);
        own[1] = T::from_primitive(other[1]);
        own[2] = T::from_primitive(other[2]);
    }
}

impl<S: Primitive, T: Primitive> FromColor<Rgba<S>> for Rgb<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Rgba<S>) {
        let rgb = &mut self.0;
        let rgba = &other.0;
        rgb[0] = T::from_primitive(rgba[0]);
        rgb[1] = T::from_primitive(rgba[1]);
        rgb[2] = T::from_primitive(rgba[2]);
    }
}

impl<S: Primitive, T: Primitive> FromColor<LumaA<S>> for Rgb<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &LumaA<S>) {
        let rgb = &mut self.0;
        let gray = other.0[0];
        rgb[0] = T::from_primitive(gray);
        rgb[1] = T::from_primitive(gray);
        rgb[2] = T::from_primitive(gray);
    }
}

impl<S: Primitive, T: Primitive> FromColor<Luma<S>> for Rgb<T>
where
    T: FromPrimitive<S>,
{
    fn from_color(&mut self, other: &Luma<S>) {
        let rgb = &mut self.0;
        let gray = other.0[0];
        rgb[0] = T::from_primitive(gray);
        rgb[1] = T::from_primitive(gray);
        rgb[2] = T::from_primitive(gray);
    }
}

/// Blends a color inter another one
pub(crate) trait Blend {
    /// Blends a color in-place.
    fn blend(&mut self, other: &Self);
}

impl<T: Primitive> Blend for LumaA<T> {
    fn blend(&mut self, other: &LumaA<T>) {
        let max_t = T::DEFAULT_MAX_VALUE;
        let max_t = max_t.to_f32().unwrap();
        let (bg_luma, bg_a) = (self.0[0], self.0[1]);
        let (fg_luma, fg_a) = (other.0[0], other.0[1]);

        let (bg_luma, bg_a) = (
            bg_luma.to_f32().unwrap() / max_t,
            bg_a.to_f32().unwrap() / max_t,
        );
        let (fg_luma, fg_a) = (
            fg_luma.to_f32().unwrap() / max_t,
            fg_a.to_f32().unwrap() / max_t,
        );

        let alpha_final = bg_a + fg_a - bg_a * fg_a;
        if alpha_final == 0.0 {
            return;
        };
        let bg_luma_a = bg_luma * bg_a;
        let fg_luma_a = fg_luma * fg_a;

        let out_luma_a = fg_luma_a + bg_luma_a * (1.0 - fg_a);
        let out_luma = out_luma_a / alpha_final;

        *self = LumaA([
            NumCast::from(max_t * out_luma).unwrap(),
            NumCast::from(max_t * alpha_final).unwrap(),
        ])
    }
}

impl<T: Primitive> Blend for Luma<T> {
    fn blend(&mut self, other: &Luma<T>) {
        *self = *other
    }
}

impl<T: Primitive> Blend for Rgba<T> {
    fn blend(&mut self, other: &Rgba<T>) {
        // http://stackoverflow.com/questions/7438263/alpha-compositing-algorithm-blend-modes#answer-11163848

        if other.0[3].is_zero() {
            return;
        }
        if other.0[3] == T::DEFAULT_MAX_VALUE {
            *self = *other;
            return;
        }

        // First, as we don't know what type our pixel is, we have to convert to floats between 0.0 and 1.0
        let max_t = T::DEFAULT_MAX_VALUE;
        let max_t = max_t.to_f32().unwrap();
        let (bg_r, bg_g, bg_b, bg_a) = (self.0[0], self.0[1], self.0[2], self.0[3]);
        let (fg_r, fg_g, fg_b, fg_a) = (other.0[0], other.0[1], other.0[2], other.0[3]);
        let (bg_r, bg_g, bg_b, bg_a) = (
            bg_r.to_f32().unwrap() / max_t,
            bg_g.to_f32().unwrap() / max_t,
            bg_b.to_f32().unwrap() / max_t,
            bg_a.to_f32().unwrap() / max_t,
        );
        let (fg_r, fg_g, fg_b, fg_a) = (
            fg_r.to_f32().unwrap() / max_t,
            fg_g.to_f32().unwrap() / max_t,
            fg_b.to_f32().unwrap() / max_t,
            fg_a.to_f32().unwrap() / max_t,
        );

        // Work out what the final alpha level will be
        let alpha_final = bg_a + fg_a - bg_a * fg_a;
        if alpha_final == 0.0 {
            return;
        };

        // We premultiply our channels by their alpha, as this makes it easier to calculate
        let (bg_r_a, bg_g_a, bg_b_a) = (bg_r * bg_a, bg_g * bg_a, bg_b * bg_a);
        let (fg_r_a, fg_g_a, fg_b_a) = (fg_r * fg_a, fg_g * fg_a, fg_b * fg_a);

        // Standard formula for src-over alpha compositing
        let (out_r_a, out_g_a, out_b_a) = (
            fg_r_a + bg_r_a * (1.0 - fg_a),
            fg_g_a + bg_g_a * (1.0 - fg_a),
            fg_b_a + bg_b_a * (1.0 - fg_a),
        );

        // Unmultiply the channels by our resultant alpha channel
        let (out_r, out_g, out_b) = (
            out_r_a / alpha_final,
            out_g_a / alpha_final,
            out_b_a / alpha_final,
        );

        // Cast back to our initial type on return
        *self = Rgba([
            NumCast::from(max_t * out_r).unwrap(),
            NumCast::from(max_t * out_g).unwrap(),
            NumCast::from(max_t * out_b).unwrap(),
            NumCast::from(max_t * alpha_final).unwrap(),
        ])
    }
}

impl<T: Primitive> Blend for Rgb<T> {
    fn blend(&mut self, other: &Rgb<T>) {
        *self = *other
    }
}

/// Invert a color
pub(crate) trait Invert {
    /// Inverts a color in-place.
    fn invert(&mut self);
}

impl<T: Primitive> Invert for LumaA<T> {
    fn invert(&mut self) {
        let l = self.0;
        let max = T::DEFAULT_MAX_VALUE;

        *self = LumaA([max - l[0], l[1]])
    }
}

impl<T: Primitive> Invert for Luma<T> {
    fn invert(&mut self) {
        let l = self.0;

        let max = T::DEFAULT_MAX_VALUE;
        let l1 = max - l[0];

        *self = Luma([l1])
    }
}

impl<T: Primitive> Invert for Rgba<T> {
    fn invert(&mut self) {
        let rgba = self.0;

        let max = T::DEFAULT_MAX_VALUE;

        *self = Rgba([max - rgba[0], max - rgba[1], max - rgba[2], rgba[3]])
    }
}

impl<T: Primitive> Invert for Rgb<T> {
    fn invert(&mut self) {
        let rgb = self.0;

        let max = T::DEFAULT_MAX_VALUE;

        let r1 = max - rgb[0];
        let g1 = max - rgb[1];
        let b1 = max - rgb[2];

        *self = Rgb([r1, g1, b1])
    }
}

#[cfg(test)]
mod tests {
    use super::{Luma, LumaA, Pixel, Rgb, Rgba};

    #[test]
    fn test_apply_with_alpha_rgba() {
        let mut rgba = Rgba([0, 0, 0, 0]);
        rgba.apply_with_alpha(|s| s, |_| 0xFF);
        assert_eq!(rgba, Rgba([0, 0, 0, 0xFF]));
    }

    #[test]
    fn test_apply_with_alpha_rgb() {
        let mut rgb = Rgb([0, 0, 0]);
        rgb.apply_with_alpha(|s| s, |_| panic!("bug"));
        assert_eq!(rgb, Rgb([0, 0, 0]));
    }

    #[test]
    fn test_map_with_alpha_rgba() {
        let rgba = Rgba([0, 0, 0, 0]).map_with_alpha(|s| s, |_| 0xFF);
        assert_eq!(rgba, Rgba([0, 0, 0, 0xFF]));
    }

    #[test]
    fn test_map_with_alpha_rgb() {
        let rgb = Rgb([0, 0, 0]).map_with_alpha(|s| s, |_| panic!("bug"));
        assert_eq!(rgb, Rgb([0, 0, 0]));
    }

    #[test]
    fn test_blend_luma_alpha() {
        let ref mut a = LumaA([255 as u8, 255]);
        let b = LumaA([255 as u8, 255]);
        a.blend(&b);
        assert_eq!(a.0[0], 255);
        assert_eq!(a.0[1], 255);

        let ref mut a = LumaA([255 as u8, 0]);
        let b = LumaA([255 as u8, 255]);
        a.blend(&b);
        assert_eq!(a.0[0], 255);
        assert_eq!(a.0[1], 255);

        let ref mut a = LumaA([255 as u8, 255]);
        let b = LumaA([255 as u8, 0]);
        a.blend(&b);
        assert_eq!(a.0[0], 255);
        assert_eq!(a.0[1], 255);

        let ref mut a = LumaA([255 as u8, 0]);
        let b = LumaA([255 as u8, 0]);
        a.blend(&b);
        assert_eq!(a.0[0], 255);
        assert_eq!(a.0[1], 0);
    }

    #[test]
    fn test_blend_rgba() {
        let ref mut a = Rgba([255 as u8, 255, 255, 255]);
        let b = Rgba([255 as u8, 255, 255, 255]);
        a.blend(&b);
        assert_eq!(a.0, [255, 255, 255, 255]);

        let ref mut a = Rgba([255 as u8, 255, 255, 0]);
        let b = Rgba([255 as u8, 255, 255, 255]);
        a.blend(&b);
        assert_eq!(a.0, [255, 255, 255, 255]);

        let ref mut a = Rgba([255 as u8, 255, 255, 255]);
        let b = Rgba([255 as u8, 255, 255, 0]);
        a.blend(&b);
        assert_eq!(a.0, [255, 255, 255, 255]);

        let ref mut a = Rgba([255 as u8, 255, 255, 0]);
        let b = Rgba([255 as u8, 255, 255, 0]);
        a.blend(&b);
        assert_eq!(a.0, [255, 255, 255, 0]);
    }

    #[test]
    fn test_apply_without_alpha_rgba() {
        let mut rgba = Rgba([0, 0, 0, 0]);
        rgba.apply_without_alpha(|s| s + 1);
        assert_eq!(rgba, Rgba([1, 1, 1, 0]));
    }

    #[test]
    fn test_apply_without_alpha_rgb() {
        let mut rgb = Rgb([0, 0, 0]);
        rgb.apply_without_alpha(|s| s + 1);
        assert_eq!(rgb, Rgb([1, 1, 1]));
    }

    #[test]
    fn test_map_without_alpha_rgba() {
        let rgba = Rgba([0, 0, 0, 0]).map_without_alpha(|s| s + 1);
        assert_eq!(rgba, Rgba([1, 1, 1, 0]));
    }

    #[test]
    fn test_map_without_alpha_rgb() {
        let rgb = Rgb([0, 0, 0]).map_without_alpha(|s| s + 1);
        assert_eq!(rgb, Rgb([1, 1, 1]));
    }

    macro_rules! test_lossless_conversion {
        ($a:ty, $b:ty, $c:ty) => {
            let a: $a = [<$a as Pixel>::Subpixel::DEFAULT_MAX_VALUE >> 2;
                <$a as Pixel>::CHANNEL_COUNT as usize]
                .into();
            let b: $b = a.into_color();
            let c: $c = b.into_color();
            assert_eq!(a.channels(), c.channels());
        };
    }

    #[test]
    fn test_lossless_conversions() {
        use super::IntoColor;
        use crate::traits::Primitive;

        test_lossless_conversion!(Luma<u8>, Luma<u16>, Luma<u8>);
        test_lossless_conversion!(LumaA<u8>, LumaA<u16>, LumaA<u8>);
        test_lossless_conversion!(Rgb<u8>, Rgb<u16>, Rgb<u8>);
        test_lossless_conversion!(Rgba<u8>, Rgba<u16>, Rgba<u8>);
    }

    #[test]
    fn accuracy_conversion() {
        use super::{Luma, Pixel, Rgb};
        let pixel = Rgb::from([13, 13, 13]);
        let Luma([luma]) = pixel.to_luma();
        assert_eq!(luma, 13);
    }
}