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
//! Encoding of PNM Images
use std::fmt;
use std::io;

use std::io::Write;

use super::AutoBreak;
use super::{ArbitraryHeader, ArbitraryTuplType, BitmapHeader, GraymapHeader, PixmapHeader};
use super::{HeaderRecord, PnmHeader, PNMSubtype, SampleEncoding};
use crate::color::{ColorType, ExtendedColorType};
use crate::error::{
    ImageError, ImageResult, ParameterError, ParameterErrorKind, UnsupportedError,
    UnsupportedErrorKind,
};
use crate::image::{ImageEncoder, ImageFormat};

use byteorder::{BigEndian, WriteBytesExt};

enum HeaderStrategy {
    Dynamic,
    Subtype(PNMSubtype),
    Chosen(PnmHeader),
}

#[derive(Clone, Copy)]
pub enum FlatSamples<'a> {
    U8(&'a [u8]),
    U16(&'a [u16]),
}

/// Encodes images to any of the `pnm` image formats.
pub struct PnmEncoder<W: Write> {
    writer: W,
    header: HeaderStrategy,
}

/// PNM Encoder
///
/// An alias of [`PnmEncoder`].
///
/// TODO: remove
///
/// [`PnmEncoder`]: struct.PnmEncoder.html
#[allow(dead_code)]
#[deprecated(note = "Use `PnmEncoder` instead")]
pub type PNMEncoder<W> = PnmEncoder<W>;

/// Encapsulate the checking system in the type system. Non of the fields are actually accessed
/// but requiring them forces us to validly construct the struct anyways.
struct CheckedImageBuffer<'a> {
    _image: FlatSamples<'a>,
    _width: u32,
    _height: u32,
    _color: ExtendedColorType,
}

// Check the header against the buffer. Each struct produces the next after a check.
struct UncheckedHeader<'a> {
    header: &'a PnmHeader,
}

struct CheckedDimensions<'a> {
    unchecked: UncheckedHeader<'a>,
    width: u32,
    height: u32,
}

struct CheckedHeaderColor<'a> {
    dimensions: CheckedDimensions<'a>,
    color: ExtendedColorType,
}

struct CheckedHeader<'a> {
    color: CheckedHeaderColor<'a>,
    encoding: TupleEncoding<'a>,
    _image: CheckedImageBuffer<'a>,
}

enum TupleEncoding<'a> {
    PbmBits {
        samples: FlatSamples<'a>,
        width: u32,
    },
    Ascii {
        samples: FlatSamples<'a>,
    },
    Bytes {
        samples: FlatSamples<'a>,
    },
}

impl<W: Write> PnmEncoder<W> {
    /// Create new PNMEncoder from the `writer`.
    ///
    /// The encoded images will have some `pnm` format. If more control over the image type is
    /// required, use either one of `with_subtype` or `with_header`. For more information on the
    /// behaviour, see `with_dynamic_header`.
    pub fn new(writer: W) -> Self {
        PnmEncoder {
            writer,
            header: HeaderStrategy::Dynamic,
        }
    }

    /// Encode a specific pnm subtype image.
    ///
    /// The magic number and encoding type will be chosen as provided while the rest of the header
    /// data will be generated dynamically. Trying to encode incompatible images (e.g. encoding an
    /// RGB image as Graymap) will result in an error.
    ///
    /// This will overwrite the effect of earlier calls to `with_header` and `with_dynamic_header`.
    pub fn with_subtype(self, subtype: PNMSubtype) -> Self {
        PnmEncoder {
            writer: self.writer,
            header: HeaderStrategy::Subtype(subtype),
        }
    }

    /// Enforce the use of a chosen header.
    ///
    /// While this option gives the most control over the actual written data, the encoding process
    /// will error in case the header data and image parameters do not agree. It is the users
    /// obligation to ensure that the width and height are set accordingly, for example.
    ///
    /// Choose this option if you want a lossless decoding/encoding round trip.
    ///
    /// This will overwrite the effect of earlier calls to `with_subtype` and `with_dynamic_header`.
    pub fn with_header(self, header: PnmHeader) -> Self {
        PnmEncoder {
            writer: self.writer,
            header: HeaderStrategy::Chosen(header),
        }
    }

    /// Create the header dynamically for each image.
    ///
    /// This is the default option upon creation of the encoder. With this, most images should be
    /// encodable but the specific format chosen is out of the users control. The pnm subtype is
    /// chosen arbitrarily by the library.
    ///
    /// This will overwrite the effect of earlier calls to `with_subtype` and `with_header`.
    pub fn with_dynamic_header(self) -> Self {
        PnmEncoder {
            writer: self.writer,
            header: HeaderStrategy::Dynamic,
        }
    }

    /// Encode an image whose samples are represented as `u8`.
    ///
    /// Some `pnm` subtypes are incompatible with some color options, a chosen header most
    /// certainly with any deviation from the original decoded image.
    pub fn encode<'s, S>(
        &mut self,
        image: S,
        width: u32,
        height: u32,
        color: ColorType,
    ) -> ImageResult<()>
    where
        S: Into<FlatSamples<'s>>,
    {
        let image = image.into();
        match self.header {
            HeaderStrategy::Dynamic => self.write_dynamic_header(image, width, height, color.into()),
            HeaderStrategy::Subtype(subtype) => {
                self.write_subtyped_header(subtype, image, width, height, color.into())
            }
            HeaderStrategy::Chosen(ref header) => {
                Self::write_with_header(&mut self.writer, header, image, width, height, color.into())
            }
        }
    }

    /// Choose any valid pnm format that the image can be expressed in and write its header.
    ///
    /// Returns how the body should be written if successful.
    fn write_dynamic_header(
        &mut self,
        image: FlatSamples,
        width: u32,
        height: u32,
        color: ExtendedColorType,
    ) -> ImageResult<()> {
        let depth = u32::from(color.channel_count());
        let (maxval, tupltype) = match color {
            ExtendedColorType::L1 => (1, ArbitraryTuplType::BlackAndWhite),
            ExtendedColorType::L8 => (0xff, ArbitraryTuplType::Grayscale),
            ExtendedColorType::L16 => (0xffff, ArbitraryTuplType::Grayscale),
            ExtendedColorType::La1 => (1, ArbitraryTuplType::BlackAndWhiteAlpha),
            ExtendedColorType::La8 => (0xff, ArbitraryTuplType::GrayscaleAlpha),
            ExtendedColorType::La16 => (0xffff, ArbitraryTuplType::GrayscaleAlpha),
            ExtendedColorType::Rgb8 => (0xff, ArbitraryTuplType::RGB),
            ExtendedColorType::Rgb16 => (0xffff, ArbitraryTuplType::RGB),
            ExtendedColorType::Rgba8 => (0xff, ArbitraryTuplType::RGBAlpha),
            ExtendedColorType::Rgba16 => (0xffff, ArbitraryTuplType::RGBAlpha),
            _ => {
                return Err(ImageError::Unsupported(
                    UnsupportedError::from_format_and_kind(
                        ImageFormat::Pnm.into(),
                        UnsupportedErrorKind::Color(color),
                    ),
                ))
            }
        };

        let header = PnmHeader {
            decoded: HeaderRecord::Arbitrary(ArbitraryHeader {
                width,
                height,
                depth,
                maxval,
                tupltype: Some(tupltype),
            }),
            encoded: None,
        };

        Self::write_with_header(&mut self.writer, &header, image, width, height, color)
    }

    /// Try to encode the image with the chosen format, give its corresponding pixel encoding type.
    fn write_subtyped_header(
        &mut self,
        subtype: PNMSubtype,
        image: FlatSamples,
        width: u32,
        height: u32,
        color: ExtendedColorType,
    ) -> ImageResult<()> {
        let header = match (subtype, color) {
            (PNMSubtype::ArbitraryMap, color) => {
                return self.write_dynamic_header(image, width, height, color)
            }
            (PNMSubtype::Pixmap(encoding), ExtendedColorType::Rgb8) => PnmHeader {
                decoded: HeaderRecord::Pixmap(PixmapHeader {
                    encoding,
                    width,
                    height,
                    maxval: 255,
                }),
                encoded: None,
            },
            (PNMSubtype::Graymap(encoding), ExtendedColorType::L8) => PnmHeader {
                decoded: HeaderRecord::Graymap(GraymapHeader {
                    encoding,
                    width,
                    height,
                    maxwhite: 255,
                }),
                encoded: None,
            },
            (PNMSubtype::Bitmap(encoding), ExtendedColorType::L8)
            | (PNMSubtype::Bitmap(encoding), ExtendedColorType::L1) => PnmHeader {
                decoded: HeaderRecord::Bitmap(BitmapHeader {
                    encoding,
                    width,
                    height,
                }),
                encoded: None,
            },
            (_, _) => {
                return Err(ImageError::Parameter(ParameterError::from_kind(
                    ParameterErrorKind::Generic(
                        "Color type can not be represented in the chosen format".to_owned(),
                    ),
                )));
            }
        };

        Self::write_with_header(&mut self.writer, &header, image, width, height, color)
    }

    /// Try to encode the image with the chosen header, checking if values are correct.
    ///
    /// Returns how the body should be written if successful.
    fn write_with_header(
        writer: &mut dyn Write,
        header: &PnmHeader,
        image: FlatSamples,
        width: u32,
        height: u32,
        color: ExtendedColorType,
    ) -> ImageResult<()> {
        let unchecked = UncheckedHeader { header };

        unchecked
            .check_header_dimensions(width, height)?
            .check_header_color(color)?
            .check_sample_values(image)?
            .write_header(writer)?
            .write_image(writer)
    }
}

impl<W: Write> ImageEncoder for PnmEncoder<W> {
    fn write_image(
        mut self,
        buf: &[u8],
        width: u32,
        height: u32,
        color_type: ColorType,
    ) -> ImageResult<()> {
        self.encode(buf, width, height, color_type)
    }
}

impl<'a> CheckedImageBuffer<'a> {
    fn check(
        image: FlatSamples<'a>,
        width: u32,
        height: u32,
        color: ExtendedColorType,
    ) -> ImageResult<CheckedImageBuffer<'a>> {
        let components = color.channel_count() as usize;
        let uwidth = width as usize;
        let uheight = height as usize;
        let expected_len = components
            .checked_mul(uwidth)
            .and_then(|v| v.checked_mul(uheight));
        if Some(image.len()) != expected_len {
            // Image buffer does not correspond to size and colour.
            return Err(ImageError::Parameter(ParameterError::from_kind(
                ParameterErrorKind::DimensionMismatch,
            )));
        }
        Ok(CheckedImageBuffer {
            _image: image,
            _width: width,
            _height: height,
            _color: color,
        })
    }
}

impl<'a> UncheckedHeader<'a> {
    fn check_header_dimensions(
        self,
        width: u32,
        height: u32,
    ) -> ImageResult<CheckedDimensions<'a>> {
        if self.header.width() != width || self.header.height() != height {
            // Chosen header does not match Image dimensions.
            return Err(ImageError::Parameter(ParameterError::from_kind(
                ParameterErrorKind::DimensionMismatch,
            )));
        }

        Ok(CheckedDimensions {
            unchecked: self,
            width,
            height,
        })
    }
}

impl<'a> CheckedDimensions<'a> {
    // Check color compatibility with the header. This will only error when we are certain that
    // the comination is bogus (e.g. combining Pixmap and Palette) but allows uncertain
    // combinations (basically a ArbitraryTuplType::Custom with any color of fitting depth).
    fn check_header_color(self, color: ExtendedColorType) -> ImageResult<CheckedHeaderColor<'a>> {
        let components = u32::from(color.channel_count());

        match *self.unchecked.header {
            PnmHeader {
                decoded: HeaderRecord::Bitmap(_),
                ..
            } => match color {
                ExtendedColorType::L1 | ExtendedColorType::L8 | ExtendedColorType::L16 => (),
                _ => {
                    return Err(ImageError::Parameter(ParameterError::from_kind(
                        ParameterErrorKind::Generic(
                            "PBM format only support luma color types".to_owned(),
                        ),
                    )))
                }
            },
            PnmHeader {
                decoded: HeaderRecord::Graymap(_),
                ..
            } => match color {
                ExtendedColorType::L1 | ExtendedColorType::L8 | ExtendedColorType::L16 => (),
                _ => {
                    return Err(ImageError::Parameter(ParameterError::from_kind(
                        ParameterErrorKind::Generic(
                            "PGM format only support luma color types".to_owned(),
                        ),
                    )))
                }
            },
            PnmHeader {
                decoded: HeaderRecord::Pixmap(_),
                ..
            } => match color {
                ExtendedColorType::Rgb8 => (),
                _ => {
                    return Err(ImageError::Parameter(ParameterError::from_kind(
                        ParameterErrorKind::Generic(
                            "PPM format only support ExtendedColorType::Rgb8".to_owned(),
                        ),
                    )))
                }
            },
            PnmHeader {
                decoded:
                    HeaderRecord::Arbitrary(ArbitraryHeader {
                        depth,
                        ref tupltype,
                        ..
                    }),
                ..
            } => match (tupltype, color) {
                (&Some(ArbitraryTuplType::BlackAndWhite), ExtendedColorType::L1) => (),
                (&Some(ArbitraryTuplType::BlackAndWhiteAlpha), ExtendedColorType::La8) => (),

                (&Some(ArbitraryTuplType::Grayscale), ExtendedColorType::L1) => (),
                (&Some(ArbitraryTuplType::Grayscale), ExtendedColorType::L8) => (),
                (&Some(ArbitraryTuplType::Grayscale), ExtendedColorType::L16) => (),
                (&Some(ArbitraryTuplType::GrayscaleAlpha), ExtendedColorType::La8) => (),

                (&Some(ArbitraryTuplType::RGB), ExtendedColorType::Rgb8) => (),
                (&Some(ArbitraryTuplType::RGBAlpha), ExtendedColorType::Rgba8) => (),

                (&None, _) if depth == components => (),
                (&Some(ArbitraryTuplType::Custom(_)), _) if depth == components => (),
                _ if depth != components => {
                    return Err(ImageError::Parameter(ParameterError::from_kind(
                        ParameterErrorKind::Generic(format!(
                            "Depth mismatch: header {} vs. color {}",
                            depth, components
                        )),
                    )))
                }
                _ => {
                    return Err(ImageError::Parameter(ParameterError::from_kind(
                        ParameterErrorKind::Generic(
                            "Invalid color type for selected PAM color type".to_owned(),
                        ),
                    )))
                }
            },
        }

        Ok(CheckedHeaderColor {
            dimensions: self,
            color,
        })
    }
}

impl<'a> CheckedHeaderColor<'a> {
    fn check_sample_values(self, image: FlatSamples<'a>) -> ImageResult<CheckedHeader<'a>> {
        let header_maxval = match self.dimensions.unchecked.header.decoded {
            HeaderRecord::Bitmap(_) => 1,
            HeaderRecord::Graymap(GraymapHeader { maxwhite, .. }) => maxwhite,
            HeaderRecord::Pixmap(PixmapHeader { maxval, .. }) => maxval,
            HeaderRecord::Arbitrary(ArbitraryHeader { maxval, .. }) => maxval,
        };

        // We trust the image color bit count to be correct at least.
        let max_sample = match self.color {
            ExtendedColorType::Unknown(n) if n <= 16 => (1 << n) - 1,
            ExtendedColorType::L1 => 1,
            ExtendedColorType::L8
            | ExtendedColorType::La8
            | ExtendedColorType::Rgb8
            | ExtendedColorType::Rgba8
            | ExtendedColorType::Bgr8
            | ExtendedColorType::Bgra8
                => 0xff,
            ExtendedColorType::L16
            | ExtendedColorType::La16
            | ExtendedColorType::Rgb16
            | ExtendedColorType::Rgba16
                => 0xffff,
            ExtendedColorType::__NonExhaustive(marker) => match marker._private {},
            _ => {
                // Unsupported target color type.
                return Err(ImageError::Unsupported(
                    UnsupportedError::from_format_and_kind(
                        ImageFormat::Pnm.into(),
                        UnsupportedErrorKind::Color(self.color),
                    ),
                ));
            }
        };

        // Avoid the performance heavy check if possible, e.g. if the header has been chosen by us.
        if header_maxval < max_sample && !image.all_smaller(header_maxval) {
            // Sample value greater than allowed for chosen header.
            return Err(ImageError::Unsupported(
                UnsupportedError::from_format_and_kind(
                    ImageFormat::Pnm.into(),
                    UnsupportedErrorKind::GenericFeature(
                        "Sample value greater than allowed for chosen header".to_owned(),
                    ),
                ),
            ));
        }

        let encoding = image.encoding_for(&self.dimensions.unchecked.header.decoded);

        let image = CheckedImageBuffer::check(
            image,
            self.dimensions.width,
            self.dimensions.height,
            self.color,
        )?;

        Ok(CheckedHeader {
            color: self,
            encoding,
            _image: image,
        })
    }
}

impl<'a> CheckedHeader<'a> {
    fn write_header(self, writer: &mut dyn Write) -> ImageResult<TupleEncoding<'a>> {
        self.header().write(writer)?;
        Ok(self.encoding)
    }

    fn header(&self) -> &PnmHeader {
        self.color.dimensions.unchecked.header
    }
}

struct SampleWriter<'a>(&'a mut dyn Write);

impl<'a> SampleWriter<'a> {
    fn write_samples_ascii<V>(self, samples: V) -> io::Result<()>
    where
        V: Iterator,
        V::Item: fmt::Display,
    {
        let mut auto_break_writer = AutoBreak::new(self.0, 70);
        for value in samples {
            write!(auto_break_writer, "{} ", value)?;
        }
        auto_break_writer.flush()
    }

    fn write_pbm_bits<V>(self, samples: &[V], width: u32) -> io::Result<()>
    /* Default gives 0 for all primitives. TODO: replace this with `Zeroable` once it hits stable */
    where
        V: Default + Eq + Copy,
    {
        // The length of an encoded scanline
        let line_width = (width - 1) / 8 + 1;

        // We'll be writing single bytes, so buffer
        let mut line_buffer = Vec::with_capacity(line_width as usize);

        for line in samples.chunks(width as usize) {
            for byte_bits in line.chunks(8) {
                let mut byte = 0u8;
                for i in 0..8 {
                    // Black pixels are encoded as 1s
                    if let Some(&v) = byte_bits.get(i) {
                        if v == V::default() {
                            byte |= 1u8 << (7 - i)
                        }
                    }
                }
                line_buffer.push(byte)
            }
            self.0.write_all(line_buffer.as_slice())?;
            line_buffer.clear();
        }

        self.0.flush()
    }
}

impl<'a> FlatSamples<'a> {
    fn len(&self) -> usize {
        match *self {
            FlatSamples::U8(arr) => arr.len(),
            FlatSamples::U16(arr) => arr.len(),
        }
    }

    fn all_smaller(&self, max_val: u32) -> bool {
        match *self {
            FlatSamples::U8(arr) => arr.iter().any(|&val| u32::from(val) > max_val),
            FlatSamples::U16(arr) => arr.iter().any(|&val| u32::from(val) > max_val),
        }
    }

    fn encoding_for(&self, header: &HeaderRecord) -> TupleEncoding<'a> {
        match *header {
            HeaderRecord::Bitmap(BitmapHeader {
                encoding: SampleEncoding::Binary,
                width,
                ..
            }) => TupleEncoding::PbmBits {
                samples: *self,
                width,
            },

            HeaderRecord::Bitmap(BitmapHeader {
                encoding: SampleEncoding::Ascii,
                ..
            }) => TupleEncoding::Ascii { samples: *self },

            HeaderRecord::Arbitrary(_) => TupleEncoding::Bytes { samples: *self },

            HeaderRecord::Graymap(GraymapHeader {
                encoding: SampleEncoding::Ascii,
                ..
            })
            | HeaderRecord::Pixmap(PixmapHeader {
                encoding: SampleEncoding::Ascii,
                ..
            }) => TupleEncoding::Ascii { samples: *self },

            HeaderRecord::Graymap(GraymapHeader {
                encoding: SampleEncoding::Binary,
                ..
            })
            | HeaderRecord::Pixmap(PixmapHeader {
                encoding: SampleEncoding::Binary,
                ..
            }) => TupleEncoding::Bytes { samples: *self },
        }
    }
}

impl<'a> From<&'a [u8]> for FlatSamples<'a> {
    fn from(samples: &'a [u8]) -> Self {
        FlatSamples::U8(samples)
    }
}

impl<'a> From<&'a [u16]> for FlatSamples<'a> {
    fn from(samples: &'a [u16]) -> Self {
        FlatSamples::U16(samples)
    }
}

impl<'a> TupleEncoding<'a> {
    fn write_image(&self, writer: &mut dyn Write) -> ImageResult<()> {
        match *self {
            TupleEncoding::PbmBits {
                samples: FlatSamples::U8(samples),
                width,
            } => SampleWriter(writer)
                .write_pbm_bits(samples, width)
                .map_err(ImageError::IoError),
            TupleEncoding::PbmBits {
                samples: FlatSamples::U16(samples),
                width,
            } => SampleWriter(writer)
                .write_pbm_bits(samples, width)
                .map_err(ImageError::IoError),

            TupleEncoding::Bytes {
                samples: FlatSamples::U8(samples),
            } => writer.write_all(samples).map_err(ImageError::IoError),
            TupleEncoding::Bytes {
                samples: FlatSamples::U16(samples),
            } => samples
                .iter()
                .try_for_each(|&sample| {
                    writer
                        .write_u16::<BigEndian>(sample)
                        .map_err(ImageError::IoError)
                }),

            TupleEncoding::Ascii {
                samples: FlatSamples::U8(samples),
            } => SampleWriter(writer)
                .write_samples_ascii(samples.iter())
                .map_err(ImageError::IoError),
            TupleEncoding::Ascii {
                samples: FlatSamples::U16(samples),
            } => SampleWriter(writer)
                .write_samples_ascii(samples.iter())
                .map_err(ImageError::IoError),
        }
    }
}