Write decoded planar data in example

examples/decode.rs

@@ -1,4 +1,4 @@
-use tiff::decoder::Decoder;
+use tiff::decoder::{BufferLayoutPreference, Decoder, DecodingBuffer, DecodingResult};
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     let Some(image) = std::env::args_os().nth(1) else {
@@ -10,10 +10,93 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let io = std::io::BufReader::new(file);
     let mut reader = Decoder::new(io)?;
 
-    while {
-        reader.read_image()?;
-        reader.more_images()
-    } {}
+    for i in 0u32.. {
+        let layout = reader.image_buffer_layout()?;
+        let colortype = reader.colortype()?;
+        let dimensions = reader.dimensions()?;
+
+        let mut data = reader.read_image()?;
+        debug_planes(i, &mut data, &layout, &colortype, dimensions);
+
+        if !reader.more_images() {
+            break;
+        }
+
+        reader.next_image()?
+    }
 
     Ok(())
 }
+
+fn debug_planes(
+    index: u32,
+    data: &mut DecodingResult,
+    layout: &BufferLayoutPreference,
+    colortype: &tiff::ColorType,
+    (width, height): (u32, u32),
+) {
+    let (depth, mut tupltype) = match colortype {
+        tiff::ColorType::Gray(_) => (1, "GRAYSCALE"),
+        tiff::ColorType::RGB(_) => (3, "RGB"),
+        tiff::ColorType::RGBA(_) => (4, "RGB_ALPHA"),
+        tiff::ColorType::Palette(_) => (1, "PALETTE"),
+        tiff::ColorType::CMYK(_) => (4, "CMYK"),
+        tiff::ColorType::Multiband { num_samples: 2, .. } => (2, "GRAYSCALE_ALPHA"),
+        _ => {
+            eprintln!("Unsupported color type for PAM output: {:?}", colortype);
+            return;
+        }
+    };
+
+    let maxval = match data.as_buffer(0) {
+        DecodingBuffer::U8(_) => u64::from(u8::MAX),
+        DecodingBuffer::U16(_) => u64::from(u16::MAX),
+        DecodingBuffer::U32(_) => u64::from(u32::MAX),
+        DecodingBuffer::U64(_) => u64::MAX,
+        // Eh, this is a good effort I guess.
+        DecodingBuffer::I8(items) => {
+            items.iter_mut().for_each(|v| *v = 0.max(*v));
+            u64::from(i8::MAX as u8)
+        }
+        DecodingBuffer::I16(items) => {
+            items.iter_mut().for_each(|v| *v = 0.max(*v));
+            u64::from(i16::MAX as u16)
+        }
+        DecodingBuffer::I32(items) => {
+            items.iter_mut().for_each(|v| *v = 0.max(*v));
+            u64::from(i32::MAX as u32)
+        }
+        DecodingBuffer::I64(items) => {
+            items.iter_mut().for_each(|v| *v = 0.max(*v));
+            i64::MAX as u64
+        }
+        // Not supported by PAM.
+        DecodingBuffer::F16(_) | DecodingBuffer::F32(_) | DecodingBuffer::F64(_) => return,
+    };
+
+    let byte_len = if layout.planes > 1 {
+        tupltype = "GRAYSCALE";
+        layout.plane_stride.unwrap().get()
+    } else {
+        data.as_buffer(0).byte_len()
+    };
+
+    // Write out this image's planes to PAM files.
+    let header = format!("P7\nWIDTH {width}\nHEIGHT {height}\nDEPTH {depth}\nMAXVAL {maxval}\nTUPLTYPE {tupltype}\nENDHDR\n");
+
+    for (plane, plane_data) in data
+        .as_buffer(0)
+        .as_bytes_mut()
+        .chunks_exact(byte_len)
+        .enumerate()
+    {
+        let filename = format!("image_{index:03}_plane_{plane:03}.pam");
+        let mut file = std::fs::File::create(filename).expect("Failed to create output file");
+
+        use std::io::Write;
+        file.write_all(header.as_bytes())
+            .expect("Failed to write PAM header");
+        file.write_all(plane_data)
+            .expect("Failed to write PAM data");
+    }
+}

src/decoder/mod.rs

@@ -110,6 +110,7 @@ impl DecodingResult {
         Self::new(size, limits, DecodingResult::I64)
     }
 
+    /// Get a view of this buffer starting from the nth _sample_ of the current type.
     pub fn as_buffer(&mut self, start: usize) -> DecodingBuffer<'_> {
         match *self {
             DecodingResult::U8(ref mut buf) => DecodingBuffer::U8(&mut buf[start..]),
@@ -154,9 +155,25 @@ pub enum DecodingBuffer<'a> {
 }
 
 impl<'a> DecodingBuffer<'a> {
-    fn as_bytes_mut(&mut self) -> &mut [u8] {
+    pub fn as_bytes(&self) -> &[u8] {
         match self {
-            DecodingBuffer::U8(ref mut buf) => buf,
+            DecodingBuffer::U8(buf) => buf,
+            DecodingBuffer::I8(buf) => bytecast::i8_as_ne_bytes(buf),
+            DecodingBuffer::U16(buf) => bytecast::u16_as_ne_bytes(buf),
+            DecodingBuffer::I16(buf) => bytecast::i16_as_ne_bytes(buf),
+            DecodingBuffer::U32(buf) => bytecast::u32_as_ne_bytes(buf),
+            DecodingBuffer::I32(buf) => bytecast::i32_as_ne_bytes(buf),
+            DecodingBuffer::U64(buf) => bytecast::u64_as_ne_bytes(buf),
+            DecodingBuffer::I64(buf) => bytecast::i64_as_ne_bytes(buf),
+            DecodingBuffer::F16(buf) => bytecast::f16_as_ne_bytes(buf),
+            DecodingBuffer::F32(buf) => bytecast::f32_as_ne_bytes(buf),
+            DecodingBuffer::F64(buf) => bytecast::f64_as_ne_bytes(buf),
+        }
+    }
+
+    pub fn as_bytes_mut(&mut self) -> &mut [u8] {
+        match self {
+            DecodingBuffer::U8(buf) => buf,
             DecodingBuffer::I8(buf) => bytecast::i8_as_ne_mut_bytes(buf),
             DecodingBuffer::U16(buf) => bytecast::u16_as_ne_mut_bytes(buf),
             DecodingBuffer::I16(buf) => bytecast::i16_as_ne_mut_bytes(buf),
@@ -170,8 +187,8 @@ impl<'a> DecodingBuffer<'a> {
         }
     }
 
-    pub fn byte_len(&mut self) -> usize {
-        self.as_bytes_mut().len()
+    pub fn byte_len(&self) -> usize {
+        self.as_bytes().len()
     }
 }