image-tiff/src/decoder/mod.rs

use num_traits::{FromPrimitive, Num};
use std::collections::HashMap;
use std::io::{self, Read, Seek};
use std::cmp;

use {ColorType, TiffError, TiffFormatError, TiffResult, TiffUnsupportedError};

use self::ifd::Directory;

use self::stream::{ByteOrder, EndianReader, LZWReader, DeflateReader, PackBitsReader, SmartReader};

pub mod ifd;
mod stream;

/// Result of a decoding process
#[derive(Debug)]
pub enum DecodingResult {
    /// A vector of unsigned bytes
    U8(Vec<u8>),
    /// A vector of unsigned words
    U16(Vec<u16>),
}

impl DecodingResult {
    fn new_u8(size: usize, limits: &Limits) -> TiffResult<DecodingResult> {
        if size > limits.decoding_buffer_size {
            Err(TiffError::LimitsExceeded)
        } else {
            Ok(DecodingResult::U8(vec![0; size]))
        }
    }

    fn new_u16(size: usize, limits: &Limits) -> TiffResult<DecodingResult> {
        if size > limits.decoding_buffer_size / 2 {
            Err(TiffError::LimitsExceeded)
        } else {
            Ok(DecodingResult::U16(vec![0; size]))
        }
    }

    pub fn as_buffer(&mut self, start: usize) -> DecodingBuffer {
        match *self {
            DecodingResult::U8(ref mut buf) => DecodingBuffer::U8(&mut buf[start..]),
            DecodingResult::U16(ref mut buf) => DecodingBuffer::U16(&mut buf[start..]),
        }
    }
}

// A buffer for image decoding
pub enum DecodingBuffer<'a> {
    /// A slice of unsigned bytes
    U8(&'a mut [u8]),
    /// A slice of unsigned words
    U16(&'a mut [u16]),
}

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

    fn byte_len(&self) -> usize {
        match *self {
            DecodingBuffer::U8(_) => 1,
            DecodingBuffer::U16(_) => 2,
        }
    }

    fn copy<'b>(&'b mut self) -> DecodingBuffer<'b>
    where
        'a: 'b,
    {
        match *self {
            DecodingBuffer::U8(ref mut buf) => DecodingBuffer::U8(buf),
            DecodingBuffer::U16(ref mut buf) => DecodingBuffer::U16(buf),
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, FromPrimitive)]
pub enum PhotometricInterpretation {
    WhiteIsZero = 0,
    BlackIsZero = 1,
    RGB = 2,
    RGBPalette = 3,
    TransparencyMask = 4,
    CMYK = 5,
    YCbCr = 6,
    CIELab = 8,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, FromPrimitive)]
pub enum CompressionMethod {
    None = 1,
    Huffman = 2,
    Fax3 = 3,
    Fax4 = 4,
    LZW = 5,
    JPEG = 6,
    Deflate = 8,
    OldDeflate = 0x80B2,
    PackBits = 0x8005,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, FromPrimitive)]
pub enum PlanarConfiguration {
    Chunky = 1,
    Planar = 2,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, FromPrimitive)]
enum Predictor {
    None = 1,
    Horizontal = 2,
}

#[derive(Debug)]
struct StripDecodeState {
    strip_index: usize,
    strip_offsets: Vec<u32>,
    strip_bytes: Vec<u32>,
}

/// Decoding limits
#[derive(Clone, Debug)]
pub struct Limits {
    /// The maximum size of any `DecodingResult` in bytes, the default is
    /// 256MiB. If the entire image is decoded at once, then this will
    /// be the maximum size of the image. If it is decoded one strip at a
    /// time, this will be the maximum size of a strip.
    pub decoding_buffer_size: usize,
    /// The maximum size of any ifd value in bytes, the default is
    /// 1MiB.
    pub ifd_value_size: usize,
    /// The purpose of this is to prevent all the fields of the struct from
    /// being public, as this would make adding new fields a major version
    /// bump.
    _non_exhaustive: (),
}

impl Default for Limits {
    fn default() -> Limits {
        Limits {
            decoding_buffer_size: 256 * 1024 * 1024,
            ifd_value_size: 1024 * 1024,
            _non_exhaustive: (),
        }
    }
}

/// The representation of a TIFF decoder
///
/// Currently does not support decoding of interlaced images
#[derive(Debug)]
pub struct Decoder<R>
where
    R: Read + Seek,
{
    reader: SmartReader<R>,
    byte_order: ByteOrder,
    limits: Limits,
    next_ifd: Option<u32>,
    ifd: Option<Directory>,
    width: u32,
    height: u32,
    bits_per_sample: Vec<u8>,
    samples: u8,
    photometric_interpretation: PhotometricInterpretation,
    compression_method: CompressionMethod,
    strip_decoder: Option<StripDecodeState>,
}

trait Wrapping {
    fn wrapping_add(&self, other: Self) -> Self;
}

impl Wrapping for u8 {
    fn wrapping_add(&self, other: Self) -> Self {
        u8::wrapping_add(*self, other)
    }
}

impl Wrapping for u16 {
    fn wrapping_add(&self, other: Self) -> Self {
        u16::wrapping_add(*self, other)
    }
}

fn rev_hpredict_nsamp<T>(image: &mut [T], size: (u32, u32), samples: usize)
where
    T: Num + Copy + Wrapping,
{
    let width = size.0 as usize;
    let height = size.1 as usize;
    for row in 0..height {
        for col in samples..width * samples {
            let prev_pixel = image[(row * width * samples + col - samples)];
            let pixel = &mut image[(row * width * samples + col)];
            *pixel = pixel.wrapping_add(prev_pixel);
        }
    }
}

fn rev_hpredict(image: DecodingBuffer, size: (u32, u32), color_type: ColorType) -> TiffResult<()> {
    let samples = match color_type {
        ColorType::Gray(8) | ColorType::Gray(16) => 1,
        ColorType::RGB(8) | ColorType::RGB(16) => 3,
        ColorType::RGBA(8) | ColorType::RGBA(16) | ColorType::CMYK(8) => 4,
        _ => {
            return Err(TiffError::UnsupportedError(
                TiffUnsupportedError::HorizontalPredictor(color_type),
            ))
        }
    };
    match image {
        DecodingBuffer::U8(buf) => {
            rev_hpredict_nsamp(buf, size, samples);
        }
        DecodingBuffer::U16(buf) => {
            rev_hpredict_nsamp(buf, size, samples);
        }
    }
    Ok(())
}

impl<R: Read + Seek> Decoder<R> {
    /// Create a new decoder that decodes from the stream ```r```
    pub fn new(r: R) -> TiffResult<Decoder<R>> {
        Decoder {
            reader: SmartReader::wrap(r, ByteOrder::LittleEndian),
            byte_order: ByteOrder::LittleEndian,
            limits: Default::default(),
            next_ifd: None,
            ifd: None,
            width: 0,
            height: 0,
            bits_per_sample: vec![1],
            samples: 1,
            photometric_interpretation: PhotometricInterpretation::BlackIsZero,
            compression_method: CompressionMethod::None,
            strip_decoder: None,
        }
        .init()
    }

    pub fn with_limits(mut self, limits: Limits) -> Decoder<R> {
        self.limits = limits;
        self
    }

    pub fn dimensions(&mut self) -> TiffResult<(u32, u32)> {
        Ok((self.width, self.height))
    }

    pub fn colortype(&mut self) -> TiffResult<ColorType> {
        match self.photometric_interpretation {
            // TODO: catch also [ 8, 8, 8, _] this does not work due to a bug in rust atm
            PhotometricInterpretation::RGB if self.bits_per_sample == [8, 8, 8, 8] => {
                Ok(ColorType::RGBA(8))
            }
            PhotometricInterpretation::RGB if self.bits_per_sample == [8, 8, 8] => {
                Ok(ColorType::RGB(8))
            }
            PhotometricInterpretation::RGB if self.bits_per_sample == [16, 16, 16, 16] => {
                Ok(ColorType::RGBA(16))
            }
            PhotometricInterpretation::RGB if self.bits_per_sample == [16, 16, 16] => {
                Ok(ColorType::RGB(16))
            }
            PhotometricInterpretation::CMYK if self.bits_per_sample == [8, 8, 8, 8] => {
                Ok(ColorType::CMYK(8))
            }
            PhotometricInterpretation::BlackIsZero | PhotometricInterpretation::WhiteIsZero
                if self.bits_per_sample.len() == 1 =>
            {
                Ok(ColorType::Gray(self.bits_per_sample[0]))
            }

            // TODO: this is bad we should not fail at this point
            _ => Err(TiffError::UnsupportedError(
                TiffUnsupportedError::InterpretationWithBits(
                    self.photometric_interpretation,
                    self.bits_per_sample.clone(),
                ),
            )),
        }
    }

    fn read_header(&mut self) -> TiffResult<()> {
        let mut endianess = Vec::with_capacity(2);
        self.reader.by_ref().take(2).read_to_end(&mut endianess)?;
        match &*endianess {
            b"II" => {
                self.byte_order = ByteOrder::LittleEndian;
                self.reader.byte_order = ByteOrder::LittleEndian;
            }
            b"MM" => {
                self.byte_order = ByteOrder::BigEndian;
                self.reader.byte_order = ByteOrder::BigEndian;
            }
            _ => {
                return Err(TiffError::FormatError(
                    TiffFormatError::TiffSignatureNotFound,
                ))
            }
        }
        if self.read_short()? != 42 {
            return Err(TiffError::FormatError(
                TiffFormatError::TiffSignatureInvalid,
            ));
        }
        self.next_ifd = match self.read_long()? {
            0 => None,
            n => Some(n),
        };
        Ok(())
    }

    /// Initializes the decoder.
    pub fn init(mut self) -> TiffResult<Decoder<R>> {
        self.read_header()?;
        self.next_image()?;
        Ok(self)
    }

    /// Reads in the next image.
    /// If there is no further image in the TIFF file a format error is returned.
    /// To determine whether there are more images call `TIFFDecoder::more_images` instead.
    pub fn next_image(&mut self) -> TiffResult<()> {
        self.ifd = Some(self.read_ifd()?);
        self.width = self.get_tag_u32(ifd::Tag::ImageWidth)?;
        self.height = self.get_tag_u32(ifd::Tag::ImageLength)?;
        self.strip_decoder = None;
        self.photometric_interpretation = match FromPrimitive::from_u32(
            self.get_tag_u32(ifd::Tag::PhotometricInterpretation)?
        ) {
            Some(val) => val,
            None => {
                return Err(TiffError::UnsupportedError(
                    TiffUnsupportedError::UnknownInterpretation,
                ))
            }
        };
        if let Some(val) = self.find_tag_u32(ifd::Tag::Compression)? {
            match FromPrimitive::from_u32(val) {
                Some(method) => self.compression_method = method,
                None => {
                    return Err(TiffError::UnsupportedError(
                        TiffUnsupportedError::UnknownCompressionMethod,
                    ))
                }
            }
        }
        if let Some(val) = self.find_tag_u32(ifd::Tag::SamplesPerPixel)? {
            self.samples = val as u8
        }
        match self.samples {
            1 => {
                if let Some(val) = self.find_tag_u32(ifd::Tag::BitsPerSample)? {
                    self.bits_per_sample = vec![val as u8]
                }
            }
            3 | 4 => {
                if let Some(val) = self.find_tag_u32_vec(ifd::Tag::BitsPerSample)? {
                    self.bits_per_sample = val.iter().map(|&v| v as u8).collect()
                }
            }
            _ => {
                return Err(TiffError::UnsupportedError(
                    TiffUnsupportedError::UnsupportedSampleDepth(self.samples),
                ))
            }
        }
        Ok(())
    }

    /// Returns `true` if there is at least one more image available.
    pub fn more_images(&self) -> bool {
        self.next_ifd.is_some()
    }

    /// Returns the byte_order
    pub fn byte_order(&self) -> ByteOrder {
        self.byte_order
    }

    /// Reads a TIFF byte value
    #[inline]
    pub fn read_byte(&mut self) -> Result<u8, io::Error> {
        let mut buf = [0; 1];
        self.reader.read_exact(&mut buf)?;
        Ok(buf[0])
    }

    /// Reads a TIFF short value
    #[inline]
    pub fn read_short(&mut self) -> Result<u16, io::Error> {
        self.reader.read_u16()
    }

    /// Reads a TIFF sshort value
    #[inline]
    pub fn read_sshort(&mut self) -> Result<i16, io::Error> {
        self.reader.read_i16()
    }

    /// Reads a TIFF long value
    #[inline]
    pub fn read_long(&mut self) -> Result<u32, io::Error> {
        self.reader.read_u32()
    }

    /// Reads a TIFF slong value
    #[inline]
    pub fn read_slong(&mut self) -> Result<i32, io::Error> {
        self.reader.read_i32()
    }

    /// Reads a string
    #[inline]
    pub fn read_string(&mut self, length: usize) -> TiffResult<String> {
        let mut out = String::with_capacity(length);
        self.reader.read_to_string(&mut out)?;
        // Strings may be null-terminated, so we trim anything downstream of the null byte
        let trimmed = out.bytes().take_while(|&n| n != 0).collect::<Vec<u8>>();
        Ok(String::from_utf8(trimmed)?)
    }

    /// Reads a TIFF IFA offset/value field
    #[inline]
    pub fn read_offset(&mut self) -> Result<[u8; 4], io::Error> {
        let mut val = [0; 4];
        self.reader.read_exact(&mut val)?;
        Ok(val)
    }

    /// Moves the cursor to the specified offset
    #[inline]
    pub fn goto_offset(&mut self, offset: u32) -> io::Result<()> {
        self.reader
            .seek(io::SeekFrom::Start(u64::from(offset)))
            .map(|_| ())
    }

    /// Reads a IFD entry.
    // An IFD entry has four fields:
    //
    // Tag   2 bytes
    // Type  2 bytes
    // Count 4 bytes
    // Value 4 bytes either a pointer the value itself
    fn read_entry(&mut self) -> TiffResult<Option<(ifd::Tag, ifd::Entry)>> {
        let tag = ifd::Tag::from_u16(self.read_short()?);
        let type_ = match ifd::Type::from_u16(self.read_short()?) {
            Some(t) => t,
            None => {
                // Unknown type. Skip this entry according to spec.
                self.read_long()?;
                self.read_long()?;
                return Ok(None);
            }
        };
        Ok(Some((
            tag,
            ifd::Entry::new(
                type_,
                self.read_long()?,   // count
                self.read_offset()?, // offset
            ),
        )))
    }

    /// Reads the next IFD
    fn read_ifd(&mut self) -> TiffResult<Directory> {
        let mut dir: Directory = HashMap::new();
        match self.next_ifd {
            None => {
                return Err(TiffError::FormatError(
                    TiffFormatError::ImageFileDirectoryNotFound,
                ))
            }
            Some(offset) => self.goto_offset(offset)?,
        }
        for _ in 0..self.read_short()? {
            let (tag, entry) = match self.read_entry()? {
                Some(val) => val,
                None => continue, // Unknown data type in tag, skip
            };
            dir.insert(tag, entry);
        }
        self.next_ifd = match self.read_long()? {
            0 => None,
            n => Some(n),
        };
        Ok(dir)
    }

    /// Tries to retrieve a tag.
    /// Return `Ok(None)` if the tag is not present.
    pub fn find_tag(&mut self, tag: ifd::Tag) -> TiffResult<Option<ifd::Value>> {
        let entry = match self.ifd.as_ref().unwrap().get(&tag) {
            None => return Ok(None),
            Some(entry) => entry.clone(),
        };

        let limits = self.limits.clone();

        Ok(Some(entry.val(&limits, self)?))
    }

    /// Tries to retrieve a tag and convert it to the desired type.
    pub fn find_tag_u32(&mut self, tag: ifd::Tag) -> TiffResult<Option<u32>> {
        match self.find_tag(tag)? {
            Some(val) => val.into_u32().map(Some),
            None => Ok(None),
        }
    }

    /// Tries to retrieve a tag and convert it to the desired type.
    pub fn find_tag_u32_vec(&mut self, tag: ifd::Tag) -> TiffResult<Option<Vec<u32>>> {
        match self.find_tag(tag)? {
            Some(val) => val.into_u32_vec().map(Some),
            None => Ok(None),
        }
    }

    /// Tries to retrieve a tag.
    /// Returns an error if the tag is not present
    pub fn get_tag(&mut self, tag: ifd::Tag) -> TiffResult<ifd::Value> {
        match self.find_tag(tag)? {
            Some(val) => Ok(val),
            None => Err(TiffError::FormatError(
                TiffFormatError::RequiredTagNotFound(tag),
            )),
        }
    }

    /// Tries to retrieve a tag and convert it to the desired type.
    pub fn get_tag_u32(&mut self, tag: ifd::Tag) -> TiffResult<u32> {
        self.get_tag(tag)?.into_u32()
    }

    /// Tries to retrieve a tag and convert it to the desired type.
    pub fn get_tag_u32_vec(&mut self, tag: ifd::Tag) -> TiffResult<Vec<u32>> {
        self.get_tag(tag)?.into_u32_vec()
    }

    /// Decompresses the strip into the supplied buffer.
    /// Returns the number of bytes read.
    fn expand_strip<'a>(
        &mut self,
        buffer: DecodingBuffer<'a>,
        offset: u32,
        length: u32,
        max_uncompressed_length: usize,
    ) -> TiffResult<usize> {
        let color_type = self.colortype()?;
        self.goto_offset(offset)?;
        let (bytes, mut reader): (usize, Box<EndianReader>) = match self.compression_method {
            CompressionMethod::None => {
                let order = self.reader.byte_order;
                (
                    length as usize,
                    Box::new(SmartReader::wrap(&mut self.reader, order)),
                )
            }
            CompressionMethod::LZW => {
                let (bytes, reader) = LZWReader::new(
                    &mut self.reader,
                    length as usize,
                    max_uncompressed_length
                )?;
                (bytes, Box::new(reader))
            }
            CompressionMethod::PackBits => {
                let order = self.reader.byte_order;
                let (bytes, reader) = PackBitsReader::new(
                    &mut self.reader,
                    order,
                    length as usize
                )?;
                (bytes, Box::new(reader))
            }
            CompressionMethod::OldDeflate => {
                let (bytes, reader) = DeflateReader::new(&mut self.reader, max_uncompressed_length)?;
                (bytes, Box::new(reader))
            }
            method => {
                return Err(TiffError::UnsupportedError(
                    TiffUnsupportedError::UnsupportedCompressionMethod(method),
                ))
            }
        };

        if bytes / buffer.byte_len() > max_uncompressed_length {
            return Err(TiffError::FormatError(
                TiffFormatError::InconsistentSizesEncountered,
            ));
        }

        Ok(match (color_type, buffer) {
            (ColorType::RGB(8), DecodingBuffer::U8(ref mut buffer))
            | (ColorType::RGBA(8), DecodingBuffer::U8(ref mut buffer))
            | (ColorType::CMYK(8), DecodingBuffer::U8(ref mut buffer)) => {
                reader.read_exact(&mut buffer[..bytes])?;
                bytes
            }
            (ColorType::RGBA(16), DecodingBuffer::U16(ref mut buffer))
            | (ColorType::RGB(16), DecodingBuffer::U16(ref mut buffer)) => {
                reader.read_u16_into(&mut buffer[..bytes / 2])?;
                bytes / 2
            }
            (ColorType::Gray(16), DecodingBuffer::U16(ref mut buffer)) => {
                reader.read_u16_into(&mut buffer[..bytes / 2])?;
                if self.photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
                    for datum in buffer[..bytes / 2].iter_mut() {
                        *datum = 0xffff - *datum
                    }
                }
                bytes / 2
            }
            (ColorType::Gray(n), DecodingBuffer::U8(ref mut buffer)) if n <= 8 => {
                reader.read_exact(&mut buffer[..bytes])?;
                if self.photometric_interpretation == PhotometricInterpretation::WhiteIsZero {
                    for byte in buffer[..bytes].iter_mut() {
                        *byte = 0xff - *byte
                    }
                }
                bytes
            }
            (type_, _) => {
                return Err(TiffError::UnsupportedError(
                    TiffUnsupportedError::UnsupportedColorType(type_),
                ))
            }
        })
    }

    /// Number of strips in image
    pub fn strip_count(&mut self) -> TiffResult<u32> {
        let rows_per_strip = self
            .get_tag_u32(ifd::Tag::RowsPerStrip)
            .unwrap_or(self.height);

        if rows_per_strip == 0 {
            return Ok(0);
        }

        Ok((self.height + rows_per_strip - 1) / rows_per_strip)
    }

    fn initialize_strip_decoder(&mut self) -> TiffResult<()> {
        if self.strip_decoder.is_none() {
            let strip_offsets = self.get_tag_u32_vec(ifd::Tag::StripOffsets)?;
            let strip_bytes = self.get_tag_u32_vec(ifd::Tag::StripByteCounts)?;

            self.strip_decoder = Some(StripDecodeState {
                strip_index: 0,
                strip_offsets,
                strip_bytes,
            });
        }
        Ok(())
    }

    pub fn read_strip_to_buffer(&mut self, mut buffer: DecodingBuffer) -> TiffResult<()> {
        self.initialize_strip_decoder()?;

        let index = self.strip_decoder.as_ref().unwrap().strip_index;
        let offset = *self
            .strip_decoder
            .as_ref()
            .unwrap()
            .strip_offsets
            .get(index)
            .ok_or(TiffError::FormatError(
                TiffFormatError::InconsistentSizesEncountered,
            ))?;
        let byte_count = *self
            .strip_decoder
            .as_ref()
            .unwrap()
            .strip_bytes
            .get(index)
            .ok_or(TiffError::FormatError(
                TiffFormatError::InconsistentSizesEncountered,
            ))?;

        let rows_per_strip = self
            .get_tag_u32(ifd::Tag::RowsPerStrip)
            .unwrap_or(self.height) as usize;

        let strip_height = cmp::min(
            rows_per_strip,
            self.height as usize - index * rows_per_strip,
        );

        let buffer_size = self.width as usize * strip_height * self.bits_per_sample.len();

        if buffer.len() < buffer_size || byte_count as usize / buffer.byte_len() > buffer_size {
            return Err(TiffError::FormatError(
                TiffFormatError::InconsistentSizesEncountered,
            ));
        }

        let units_read = self.expand_strip(buffer.copy(), offset, byte_count, buffer_size)?;

        self.strip_decoder.as_mut().unwrap().strip_index += 1;

        if index as u32 == self.strip_count()? {
            self.strip_decoder = None;
        }

        if units_read < buffer_size {
            return Err(TiffError::FormatError(
                TiffFormatError::InconsistentSizesEncountered,
            ));
        }
        if let Ok(predictor) = self.get_tag_u32(ifd::Tag::Predictor) {
            match FromPrimitive::from_u32(predictor) {
                Some(Predictor::None) => (),
                Some(Predictor::Horizontal) => {
                    rev_hpredict(
                        buffer.copy(),
                        (self.width, strip_height as u32),
                        self.colortype()?,
                    )?;
                }
                None => {
                    return Err(TiffError::FormatError(TiffFormatError::UnknownPredictor(
                        predictor,
                    )))
                }
            }
        }
        Ok(())
    }

    /// Read a single strip from the image and return it as a Vector
    pub fn read_strip(&mut self) -> TiffResult<DecodingResult> {
        self.initialize_strip_decoder()?;
        let index = self.strip_decoder.as_ref().unwrap().strip_index;

        let rows_per_strip = self
            .get_tag_u32(ifd::Tag::RowsPerStrip)
            .unwrap_or(self.height) as usize;

        let strip_height = cmp::min(
            rows_per_strip,
            self.height as usize - index * rows_per_strip,
        );

        let buffer_size = self.width as usize * strip_height * self.bits_per_sample.iter().count();

        let mut result = match self.bits_per_sample.iter().cloned().max().unwrap_or(8) {
            n if n <= 8 => DecodingResult::new_u8(buffer_size, &self.limits)?,
            n if n <= 16 => DecodingResult::new_u16(buffer_size, &self.limits)?,
            n => {
                return Err(TiffError::UnsupportedError(
                    TiffUnsupportedError::UnsupportedBitsPerChannel(n),
                ))
            }
        };

        self.read_strip_to_buffer(result.as_buffer(0))?;

        Ok(result)
    }

    /// Decodes the entire image and return it as a Vector
    pub fn read_image(&mut self) -> TiffResult<DecodingResult> {
        self.initialize_strip_decoder()?;
        let rows_per_strip = self
            .get_tag_u32(ifd::Tag::RowsPerStrip)
            .unwrap_or(self.height) as usize;

        let samples_per_strip =
            self.width as usize * rows_per_strip * self.bits_per_sample.iter().count();

        let buffer_size =
            self.width as usize * self.height as usize * self.bits_per_sample.iter().count();

        let mut result = match self.bits_per_sample.iter().cloned().max().unwrap_or(8) {
            n if n <= 8 => DecodingResult::new_u8(buffer_size, &self.limits)?,
            n if n <= 16 => DecodingResult::new_u16(buffer_size, &self.limits)?,
            n => {
                return Err(TiffError::UnsupportedError(
                    TiffUnsupportedError::UnsupportedBitsPerChannel(n),
                ))
            }
        };

        for i in 0..self.strip_count()? as usize {
            self.read_strip_to_buffer(result.as_buffer(samples_per_strip * i))?;
        }

        Ok(result)
    }
}