add CMYKA (#208)

src/decoder/image.rs

@@ -330,6 +330,7 @@ impl Image {
             },
             PhotometricInterpretation::CMYK => match self.samples {
                 4 => Ok(ColorType::CMYK(self.bits_per_sample)),
+                5 => Ok(ColorType::CMYKA(self.bits_per_sample)),
                 _ => Err(TiffError::UnsupportedError(
                     TiffUnsupportedError::InterpretationWithBits(
                         self.photometric_interpretation,
@@ -567,6 +568,7 @@ impl Image {
             ColorType::RGB(n)
             | ColorType::RGBA(n)
             | ColorType::CMYK(n)
+            | ColorType::CMYKA(n)
             | ColorType::YCbCr(n)
             | ColorType::Gray(n)
             | ColorType::Multiband {

src/encoder/colortype.rs

@@ -341,3 +341,13 @@ impl ColorType for YCbCr8 {
 
     integer_horizontal_predict!();
 }
+
+pub struct CMYKA8;
+impl ColorType for CMYKA8 {
+    type Inner = u8;
+    const TIFF_VALUE: PhotometricInterpretation = PhotometricInterpretation::CMYK;
+    const BITS_PER_SAMPLE: &'static [u16] = &[8, 8, 8, 8, 8];
+    const SAMPLE_FORMAT: &'static [SampleFormat] = &[SampleFormat::Uint; 5];
+
+    integer_horizontal_predict!();
+}

src/lib.rs

@@ -16,6 +16,7 @@ pub use self::error::{TiffError, TiffFormatError, TiffResult, TiffUnsupportedErr
 
 /// An enumeration over supported color types and their bit depths
 #[derive(Copy, PartialEq, Eq, Debug, Clone, Hash)]
+#[non_exhaustive]
 pub enum ColorType {
     /// Pixel is grayscale
     Gray(u8),
@@ -35,6 +36,9 @@ pub enum ColorType {
     /// Pixel is CMYK
     CMYK(u8),
 
+    /// Pixel is CMYK with an alpha channel
+    CMYKA(u8),
+
     /// Pixel is YCbCr
     YCbCr(u8),
 
@@ -50,6 +54,7 @@ impl ColorType {
             | ColorType::GrayA(b)
             | ColorType::RGBA(b)
             | ColorType::CMYK(b)
+            | ColorType::CMYKA(b)
             | ColorType::YCbCr(b)
             | ColorType::Multiband { bit_depth: b, .. } => b,
         }