Support 16-bit encoded TGA images.

The decoder does the same thing as the BMP decoder, and converts 16-bit images to 32-bit ones on load.

Author: red-001

src/codecs/bmp/decoder.rs

@@ -13,28 +13,16 @@ use crate::error::{
 use crate::image::{self, ImageDecoder, ImageFormat};
 use crate::ImageDecoderRect;
 
+use crate::utils::packed_color::Bitfield;
+use crate::utils::packed_color::{BitfieldError, Bitfields};
+
 const BITMAPCOREHEADER_SIZE: u32 = 12;
 const BITMAPINFOHEADER_SIZE: u32 = 40;
 const BITMAPV2HEADER_SIZE: u32 = 52;
 const BITMAPV3HEADER_SIZE: u32 = 56;
 const BITMAPV4HEADER_SIZE: u32 = 108;
 const BITMAPV5HEADER_SIZE: u32 = 124;
 
-static LOOKUP_TABLE_3_BIT_TO_8_BIT: [u8; 8] = [0, 36, 73, 109, 146, 182, 219, 255];
-static LOOKUP_TABLE_4_BIT_TO_8_BIT: [u8; 16] = [
-    0, 17, 34, 51, 68, 85, 102, 119, 136, 153, 170, 187, 204, 221, 238, 255,
-];
-static LOOKUP_TABLE_5_BIT_TO_8_BIT: [u8; 32] = [
-    0, 8, 16, 25, 33, 41, 49, 58, 66, 74, 82, 90, 99, 107, 115, 123, 132, 140, 148, 156, 165, 173,
-    181, 189, 197, 206, 214, 222, 230, 239, 247, 255,
-];
-static LOOKUP_TABLE_6_BIT_TO_8_BIT: [u8; 64] = [
-    0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 45, 49, 53, 57, 61, 65, 69, 73, 77, 81, 85, 89, 93,
-    97, 101, 105, 109, 113, 117, 121, 125, 130, 134, 138, 142, 146, 150, 154, 158, 162, 166, 170,
-    174, 178, 182, 186, 190, 194, 198, 202, 206, 210, 215, 219, 223, 227, 231, 235, 239, 243, 247,
-    251, 255,
-];
-
 static R5_G5_B5_COLOR_MASK: Bitfields = Bitfields {
     r: Bitfield { len: 5, shift: 10 },
     g: Bitfield { len: 5, shift: 5 },
@@ -120,14 +108,8 @@ enum DecoderError {
     // Failed to decompress RLE data.
     CorruptRleData,
 
-    /// The bitfield mask interleaves set and unset bits
-    BitfieldMaskNonContiguous,
-    /// Bitfield mask invalid (e.g. too long for specified type)
-    BitfieldMaskInvalid,
-    /// Bitfield (of the specified width – 16- or 32-bit) mask not present
-    BitfieldMaskMissing(u32),
     /// Bitfield (of the specified width – 16- or 32-bit) masks not present
-    BitfieldMasksMissing(u32),
+    BitfieldError(BitfieldError),
 
     /// BMP's "BM" signature wrong or missing
     BmpSignatureInvalid,
@@ -164,13 +146,8 @@ impl fmt::Display for DecoderError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             DecoderError::CorruptRleData => f.write_str("Corrupt RLE data"),
-            DecoderError::BitfieldMaskNonContiguous => f.write_str("Non-contiguous bitfield mask"),
-            DecoderError::BitfieldMaskInvalid => f.write_str("Invalid bitfield mask"),
-            DecoderError::BitfieldMaskMissing(bb) => {
-                f.write_fmt(format_args!("Missing {bb}-bit bitfield mask"))
-            }
-            DecoderError::BitfieldMasksMissing(bb) => {
-                f.write_fmt(format_args!("Missing {bb}-bit bitfield masks"))
+            DecoderError::BitfieldError(bb) => {
+                f.write_fmt(format_args!("Bitfield error: {bb}"))
             }
             DecoderError::BmpSignatureInvalid => f.write_str("BMP signature not found"),
             DecoderError::MoreThanOnePlane => f.write_str("More than one plane"),
@@ -207,6 +184,15 @@ impl From<DecoderError> for ImageError {
     }
 }
 
+impl From<BitfieldError> for ImageError {
+    fn from(e: BitfieldError) -> ImageError {
+        ImageError::Decoding(DecodingError::new(
+            ImageFormat::Bmp.into(),
+            DecoderError::BitfieldError(e),
+        ))
+    }
+}
+
 impl error::Error for DecoderError {}
 
 /// Distinct image types whose saved channel width can be invalid
@@ -397,77 +383,6 @@ fn set_1bit_pixel_run<'a, T: Iterator<Item = &'a u8>>(
     }
 }
 
-#[derive(PartialEq, Eq)]
-struct Bitfield {
-    shift: u32,
-    len: u32,
-}
-
-impl Bitfield {
-    fn from_mask(mask: u32, max_len: u32) -> ImageResult<Bitfield> {
-        if mask == 0 {
-            return Ok(Bitfield { shift: 0, len: 0 });
-        }
-        let mut shift = mask.trailing_zeros();
-        let mut len = (!(mask >> shift)).trailing_zeros();
-        if len != mask.count_ones() {
-            return Err(DecoderError::BitfieldMaskNonContiguous.into());
-        }
-        if len + shift > max_len {
-            return Err(DecoderError::BitfieldMaskInvalid.into());
-        }
-        if len > 8 {
-            shift += len - 8;
-            len = 8;
-        }
-        Ok(Bitfield { shift, len })
-    }
-
-    fn read(&self, data: u32) -> u8 {
-        let data = data >> self.shift;
-        match self.len {
-            1 => ((data & 0b1) * 0xff) as u8,
-            2 => ((data & 0b11) * 0x55) as u8,
-            3 => LOOKUP_TABLE_3_BIT_TO_8_BIT[(data & 0b00_0111) as usize],
-            4 => LOOKUP_TABLE_4_BIT_TO_8_BIT[(data & 0b00_1111) as usize],
-            5 => LOOKUP_TABLE_5_BIT_TO_8_BIT[(data & 0b01_1111) as usize],
-            6 => LOOKUP_TABLE_6_BIT_TO_8_BIT[(data & 0b11_1111) as usize],
-            7 => ((data & 0x7f) << 1 | (data & 0x7f) >> 6) as u8,
-            8 => (data & 0xff) as u8,
-            _ => panic!(),
-        }
-    }
-}
-
-#[derive(PartialEq, Eq)]
-struct Bitfields {
-    r: Bitfield,
-    g: Bitfield,
-    b: Bitfield,
-    a: Bitfield,
-}
-
-impl Bitfields {
-    fn from_mask(
-        r_mask: u32,
-        g_mask: u32,
-        b_mask: u32,
-        a_mask: u32,
-        max_len: u32,
-    ) -> ImageResult<Bitfields> {
-        let bitfields = Bitfields {
-            r: Bitfield::from_mask(r_mask, max_len)?,
-            g: Bitfield::from_mask(g_mask, max_len)?,
-            b: Bitfield::from_mask(b_mask, max_len)?,
-            a: Bitfield::from_mask(a_mask, max_len)?,
-        };
-        if bitfields.r.len == 0 || bitfields.g.len == 0 || bitfields.b.len == 0 {
-            return Err(DecoderError::BitfieldMaskMissing(max_len).into());
-        }
-        Ok(bitfields)
-    }
-}
-
 /// A bmp decoder
 pub struct BmpDecoder<R> {
     reader: R,
@@ -1308,7 +1223,7 @@ impl<R: BufRead + Seek> BmpDecoder<R> {
             ImageType::RLE4 => self.read_rle_data(buf, ImageType::RLE4),
             ImageType::Bitfields16 => match self.bitfields {
                 Some(_) => self.read_16_bit_pixel_data(buf, None),
-                None => Err(DecoderError::BitfieldMasksMissing(16).into()),
+                None => Err(BitfieldError::MasksMissing(16).into()),
             },
             ImageType::Bitfields32 => match self.bitfields {
                 Some(R8_G8_B8_COLOR_MASK) => {
@@ -1318,7 +1233,7 @@ impl<R: BufRead + Seek> BmpDecoder<R> {
                     self.read_full_byte_pixel_data(buf, &FormatFullBytes::RGBA32)
                 }
                 Some(_) => self.read_32_bit_pixel_data(buf),
-                None => Err(DecoderError::BitfieldMasksMissing(32).into()),
+                None => Err(BitfieldError::MasksMissing(32).into()),
             },
         }
     }

src/codecs/tga/decoder.rs

@@ -2,12 +2,29 @@ use super::header::{Header, ImageType, ALPHA_BIT_MASK, SCREEN_ORIGIN_BIT_MASK};
 use crate::{
     color::{ColorType, ExtendedColorType},
     error::{
-        ImageError, ImageResult, LimitError, LimitErrorKind, UnsupportedError, UnsupportedErrorKind,
+        ImageError, ImageFormatHint, ImageResult, LimitError, LimitErrorKind, UnsupportedError,
+        UnsupportedErrorKind,
     },
     image::{ImageDecoder, ImageFormat},
+    utils::packed_color::{Bitfield, Bitfields},
+};
+use byteorder_lite::{LittleEndian, ReadBytesExt};
+use num_traits::ToPrimitive;
+use std::io::{self, Cursor, Read};
+
+static R5_G5_B5_COLOR_MASK: Bitfields = Bitfields {
+    r: Bitfield { len: 5, shift: 10 },
+    g: Bitfield { len: 5, shift: 5 },
+    b: Bitfield { len: 5, shift: 0 },
+    a: Bitfield { len: 0, shift: 0 },
+};
+
+static R5_G5_B5_A1_COLOR_MASK: Bitfields = Bitfields {
+    r: Bitfield { len: 5, shift: 10 },
+    g: Bitfield { len: 5, shift: 5 },
+    b: Bitfield { len: 5, shift: 0 },
+    a: Bitfield { len: 1, shift: 15 },
 };
-use byteorder_lite::ReadBytesExt;
-use std::io::{self, Read};
 
 struct ColorMap {
     /// sizes in bytes
@@ -57,6 +74,8 @@ pub struct TgaDecoder<R> {
 
     header: Header,
     color_map: Option<ColorMap>,
+
+    packing: Option<&'static Bitfields>,
 }
 
 impl<R: Read> TgaDecoder<R> {
@@ -76,6 +95,8 @@ impl<R: Read> TgaDecoder<R> {
 
             header: Header::default(),
             color_map: None,
+
+            packing: None,
         };
         decoder.read_metadata()?;
         Ok(decoder)
@@ -152,6 +173,16 @@ impl<R: Read> TgaDecoder<R> {
                 self.color_type = ColorType::L8;
                 self.original_color_type = Some(ExtendedColorType::A8);
             }
+            (0, 15, false) => {
+                self.color_type = ColorType::Rgb8;
+                self.original_color_type = Some(ExtendedColorType::Rgb5);
+                self.packing = Some(&R5_G5_B5_COLOR_MASK);
+            }
+            (1, 15, true) => {
+                self.color_type = ColorType::Rgba8;
+                self.original_color_type = Some(ExtendedColorType::Rgb5a1);
+                self.packing = Some(&R5_G5_B5_A1_COLOR_MASK);
+            }
             _ => {
                 return Err(ImageError::Unsupported(
                     UnsupportedError::from_format_and_kind(
@@ -350,16 +381,21 @@ impl<R: Read> ImageDecoder for TgaDecoder<R> {
             .unwrap_or_else(|| self.color_type().into())
     }
 
+    #[allow(clippy::identity_op)]
     fn read_image(mut self, buf: &mut [u8]) -> ImageResult<()> {
         assert_eq!(u64::try_from(buf.len()), Ok(self.total_bytes()));
 
         // In indexed images, we might need more bytes than pixels to read them. That's nonsensical
         // to encode but we'll not want to crash.
+        //
+        // also used for packed (<8 bit per channel) images
         let mut fallback_buf = vec![];
         // read the pixels from the data region
         let rawbuf = if self.image_type.is_encoded() {
             let pixel_data = self.read_all_encoded_data()?;
-            if self.bytes_per_pixel <= usize::from(self.color_type.bytes_per_pixel()) {
+            if self.bytes_per_pixel <= usize::from(self.color_type.bytes_per_pixel())
+                && self.packing.is_none()
+            {
                 buf[..pixel_data.len()].copy_from_slice(&pixel_data);
                 &buf[..pixel_data.len()]
             } else {
@@ -368,7 +404,9 @@ impl<R: Read> ImageDecoder for TgaDecoder<R> {
             }
         } else {
             let num_raw_bytes = self.width * self.height * self.bytes_per_pixel;
-            if self.bytes_per_pixel <= usize::from(self.color_type.bytes_per_pixel()) {
+            if self.bytes_per_pixel <= usize::from(self.color_type.bytes_per_pixel())
+                && self.packing.is_none()
+            {
                 self.r.by_ref().read_exact(&mut buf[..num_raw_bytes])?;
                 &buf[..num_raw_bytes]
             } else {
@@ -389,10 +427,55 @@ impl<R: Read> ImageDecoder for TgaDecoder<R> {
                     LimitErrorKind::DimensionError,
                 )));
             }
-            buf.copy_from_slice(&pixel_data);
+
+            if self.packing.is_none() {
+                buf.copy_from_slice(&pixel_data);
+            } else {
+                fallback_buf.resize(buf.len(), 0);
+                fallback_buf.copy_from_slice(&pixel_data);
+            }
         }
 
-        self.reverse_encoding_in_output(buf);
+        if let Some(bitfields) = &self.packing {
+            let num_pixels = self.width * self.height;
+            let bytes_per_unpacked_pixel = if bitfields.a.len > 0 { 4 } else { 3 };
+            let mut stream = Cursor::new(fallback_buf);
+            let bytes_per_packed_pixel = self.bytes_per_pixel;
+
+            // this check shouldn't get hit, unsupported formats should have been rejected in `read_color_information`
+            // but it seemed better to check this here instead of panicing below if there is an issue
+            if !(1..=3).contains(&bytes_per_packed_pixel) {
+                return Err(ImageError::Unsupported(
+                    UnsupportedError::from_format_and_kind(
+                        ImageFormatHint::Exact(ImageFormat::Tga),
+                        UnsupportedErrorKind::GenericFeature(
+                            "Unsupported packed pixel format".to_string(),
+                        ),
+                    ),
+                ));
+            }
+
+            for i in 0..num_pixels {
+                let value = match bytes_per_packed_pixel {
+                    1 => stream.read_u8().map(|i| -> u32 { i.to_u32().unwrap() }),
+                    2 => stream
+                        .read_u16::<LittleEndian>()
+                        .map(|i| -> u32 { i.to_u32().unwrap() }),
+                    3 => stream.read_u24::<LittleEndian>(),
+                    _ => unimplemented!(),
+                }
+                .map_err(|e| -> ImageError { ImageError::IoError(e) })?;
+
+                buf[i * bytes_per_unpacked_pixel + 0] = bitfields.r.read(value);
+                buf[i * bytes_per_unpacked_pixel + 1] = bitfields.g.read(value);
+                buf[i * bytes_per_unpacked_pixel + 2] = bitfields.b.read(value);
+                if bytes_per_unpacked_pixel == 4 {
+                    buf[i * bytes_per_unpacked_pixel + 3] = bitfields.a.read(value);
+                }
+            }
+        } else {
+            self.reverse_encoding_in_output(buf);
+        }
 
         self.flip_vertically(buf);
 

src/color.rs

@@ -120,6 +120,10 @@ pub enum ExtendedColorType {
     Rgb4,
     /// Pixel is 4-bit RGB with an alpha channel
     Rgba4,
+    /// Pixel is 5-bit RGB with one unused bit
+    Rgb5,
+    /// Pixel is 5-bit RGB with one bit alpha
+    Rgb5a1,
     /// Pixel is 8-bit luminance
     L8,
     /// Pixel is 8-bit luminance with an alpha channel
@@ -179,13 +183,15 @@ impl ExtendedColorType {
             ExtendedColorType::Rgb1
             | ExtendedColorType::Rgb2
             | ExtendedColorType::Rgb4
+            | ExtendedColorType::Rgb5
             | ExtendedColorType::Rgb8
             | ExtendedColorType::Rgb16
             | ExtendedColorType::Rgb32F
             | ExtendedColorType::Bgr8 => 3,
             ExtendedColorType::Rgba1
             | ExtendedColorType::Rgba2
             | ExtendedColorType::Rgba4
+            | ExtendedColorType::Rgb5a1
             | ExtendedColorType::Rgba8
             | ExtendedColorType::Rgba16
             | ExtendedColorType::Rgba32F
@@ -213,6 +219,8 @@ impl ExtendedColorType {
             ExtendedColorType::Rgba4 => 16,
             ExtendedColorType::L8 => 8,
             ExtendedColorType::La8 => 16,
+            ExtendedColorType::Rgb5 => 16, // somewhat of a lie, it's actually 15 bits of image data and one unused bit.
+            ExtendedColorType::Rgb5a1 => 16,
             ExtendedColorType::Rgb8 => 24,
             ExtendedColorType::Rgba8 => 32,
             ExtendedColorType::L16 => 16,

src/utils/mod.rs

@@ -2,6 +2,8 @@
 
 use std::iter::repeat;
 
+pub(crate) mod packed_color;
+
 #[inline(always)]
 pub(crate) fn expand_packed<F>(buf: &mut [u8], channels: usize, bit_depth: u8, mut func: F)
 where