Merge georust#246

246: Implement ColorTable struct r=ChristianBeilschmidt,lnicola a=Barugon

Implement a `ColorTable` struct and add a `RasterBand::color_table` method.

- [x] I agree to follow the project's [code of conduct](https://github.com/georust/gdal/blob/master/CODE_OF_CONDUCT.md).
- [x] I added an entry to `CHANGES.md`.
---



Co-authored-by: Barugon <[email protected]>

CHANGES.md

@@ -27,6 +27,10 @@
 
   - <https://github.com/georust/gdal/pull/257>
 
+- Add a `ColorTable` struct and `RasterBand::color_table` method
+
+  - <https://github.com/georust/gdal/pull/246>
+
 ## 0.12
 
 - Bump Rust edition to 2021

src/raster/mod.rs

@@ -5,7 +5,10 @@ mod rasterize;
 mod types;
 mod warp;
 
-pub use rasterband::{Buffer, ByteBuffer, ColorInterpretation, RasterBand, ResampleAlg};
+pub use rasterband::{
+    Buffer, ByteBuffer, CmykEntry, ColorEntry, ColorInterpretation, ColorTable, GrayEntry,
+    HlsEntry, PaletteInterpretation, RasterBand, ResampleAlg, RgbaEntry,
+};
 pub use rasterize::{rasterize, BurnSource, MergeAlgorithm, OptimizeMode, RasterizeOptions};
 pub use types::{GDALDataType, GdalType};
 pub use warp::reproject;

src/raster/rasterband.rs

@@ -4,11 +4,12 @@ use crate::metadata::Metadata;
 use crate::raster::{GDALDataType, GdalType};
 use crate::utils::{_last_cpl_err, _last_null_pointer_err, _string};
 use gdal_sys::{
-    self, CPLErr, GDALColorInterp, GDALMajorObjectH, GDALRWFlag, GDALRasterBandH,
-    GDALRasterIOExtraArg,
+    self, CPLErr, GDALColorEntry, GDALColorInterp, GDALColorTableH, GDALMajorObjectH,
+    GDALPaletteInterp, GDALRWFlag, GDALRasterBandH, GDALRasterIOExtraArg,
 };
 use libc::c_int;
 use std::ffi::CString;
+use std::marker::PhantomData;
 
 #[cfg(feature = "ndarray")]
 use ndarray::Array2;
@@ -421,6 +422,15 @@ impl<'a> RasterBand<'a> {
         Ok(())
     }
 
+    /// Get the color table for this band if it has one.
+    pub fn color_table(&self) -> Option<ColorTable> {
+        let c_color_table = unsafe { gdal_sys::GDALGetRasterColorTable(self.c_rasterband) };
+        if c_color_table.is_null() {
+            return None;
+        }
+        Some(ColorTable::from_c_color_table(c_color_table))
+    }
+
     /// Returns the scale of this band if set.
     pub fn scale(&self) -> Option<f64> {
         let mut pb_success = 1;
@@ -612,3 +622,144 @@ impl ColorInterpretation {
         _string(rv)
     }
 }
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum PaletteInterpretation {
+    Gray,
+    Rgba,
+    Cmyk,
+    Hls,
+}
+
+impl PaletteInterpretation {
+    fn from_c_int(palette_interpretation: GDALPaletteInterp::Type) -> Self {
+        match palette_interpretation {
+            GDALPaletteInterp::GPI_Gray => Self::Gray,
+            GDALPaletteInterp::GPI_RGB => Self::Rgba,
+            GDALPaletteInterp::GPI_CMYK => Self::Cmyk,
+            GDALPaletteInterp::GPI_HLS => Self::Hls,
+            _ => unreachable!("GDAL has implemented a new type of `GDALPaletteInterp`"),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct GrayEntry {
+    pub g: i16,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct RgbaEntry {
+    pub r: i16,
+    pub g: i16,
+    pub b: i16,
+    pub a: i16,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct CmykEntry {
+    pub c: i16,
+    pub m: i16,
+    pub y: i16,
+    pub k: i16,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct HlsEntry {
+    pub h: i16,
+    pub l: i16,
+    pub s: i16,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum ColorEntry {
+    Gray(GrayEntry),
+    Rgba(RgbaEntry),
+    Cmyk(CmykEntry),
+    Hls(HlsEntry),
+}
+
+/// Color table for raster bands that use the PaletteIndex color interpretation.
+///
+/// This object carries the lifetime of the raster band that
+/// contains it. This is necessary to prevent the raster band
+/// from being dropped before the color table.
+pub struct ColorTable<'a> {
+    palette_interpretation: PaletteInterpretation,
+    c_color_table: GDALColorTableH,
+    phantom_raster_band: PhantomData<&'a RasterBand<'a>>,
+}
+
+impl<'a> ColorTable<'a> {
+    fn from_c_color_table(c_color_table: GDALColorTableH) -> Self {
+        let interp_index = unsafe { gdal_sys::GDALGetPaletteInterpretation(c_color_table) };
+        ColorTable {
+            palette_interpretation: PaletteInterpretation::from_c_int(interp_index),
+            c_color_table,
+            phantom_raster_band: PhantomData,
+        }
+    }
+
+    /// How the values of this color table are interpreted.
+    pub fn palette_interpretation(&self) -> PaletteInterpretation {
+        self.palette_interpretation
+    }
+
+    /// Get the number of color entries in this color table.
+    pub fn entry_count(&self) -> usize {
+        unsafe { gdal_sys::GDALGetColorEntryCount(self.c_color_table) as usize }
+    }
+
+    /// Get a color entry.
+    pub fn entry(&self, index: usize) -> Option<ColorEntry> {
+        let color_entry = unsafe {
+            let c_color_entry = gdal_sys::GDALGetColorEntry(self.c_color_table, index as i32);
+            if c_color_entry.is_null() {
+                return None;
+            }
+            *c_color_entry
+        };
+        match self.palette_interpretation {
+            PaletteInterpretation::Gray => Some(ColorEntry::Gray(GrayEntry { g: color_entry.c1 })),
+            PaletteInterpretation::Rgba => Some(ColorEntry::Rgba(RgbaEntry {
+                r: color_entry.c1,
+                g: color_entry.c2,
+                b: color_entry.c3,
+                a: color_entry.c4,
+            })),
+            PaletteInterpretation::Cmyk => Some(ColorEntry::Cmyk(CmykEntry {
+                c: color_entry.c1,
+                m: color_entry.c2,
+                y: color_entry.c3,
+                k: color_entry.c4,
+            })),
+            PaletteInterpretation::Hls => Some(ColorEntry::Hls(HlsEntry {
+                h: color_entry.c1,
+                l: color_entry.c2,
+                s: color_entry.c3,
+            })),
+        }
+    }
+
+    /// Get a color entry as RGB.
+    pub fn entry_as_rgb(&self, index: usize) -> Option<RgbaEntry> {
+        let mut color_entry = GDALColorEntry {
+            c1: 0,
+            c2: 0,
+            c3: 0,
+            c4: 0,
+        };
+        if unsafe {
+            gdal_sys::GDALGetColorEntryAsRGB(self.c_color_table, index as i32, &mut color_entry)
+        } == 0
+        {
+            return None;
+        }
+        Some(RgbaEntry {
+            r: color_entry.c1,
+            g: color_entry.c2,
+            b: color_entry.c3,
+            a: color_entry.c4,
+        })
+    }
+}

src/raster/tests.rs

@@ -706,3 +706,43 @@ fn test_rasterband_unit() {
 
     assert_eq!(rasterband.unit(), "m".to_string());
 }
+
+#[test]
+fn test_color_table() {
+    use crate::raster::rasterband::{ColorEntry, PaletteInterpretation};
+
+    // Raster containing one band.
+    let dataset = Dataset::open(fixture!("test_color_table.tif")).expect("open failure");
+    assert_eq!(dataset.raster_count(), 1);
+
+    // Band is PaletteIndex.
+    let band = dataset.rasterband(1).expect("rasterband failure");
+    assert_eq!(
+        band.color_interpretation(),
+        ColorInterpretation::PaletteIndex
+    );
+
+    // Color table is RGB.
+    let color_table = band.color_table().unwrap();
+    assert_eq!(
+        color_table.palette_interpretation(),
+        PaletteInterpretation::Rgba
+    );
+
+    // Color table has 256 entries.
+    let entry_count = color_table.entry_count();
+    assert_eq!(entry_count, 256);
+
+    // Check that entry and entry_as_rgb are the same.
+    for index in 0..entry_count {
+        if let ColorEntry::Rgba(entry) = color_table.entry(index).unwrap() {
+            let rgb_entry = color_table.entry_as_rgb(index).unwrap();
+            assert_eq!(entry.r, rgb_entry.r);
+            assert_eq!(entry.g, rgb_entry.g);
+            assert_eq!(entry.b, rgb_entry.b);
+            assert_eq!(entry.a, rgb_entry.a);
+        } else {
+            panic!();
+        }
+    }
+}