feat(geotiff): Add colorinterp property

packages/geotiff/src/colorinterp.ts

@@ -0,0 +1,67 @@
+import { Photometric } from "@cogeotiff/core";
+import { ExtraSample } from "./ifd.js";
+
+export enum ColorInterp {
+  UNDEFINED = "undefined",
+  GRAY = "gray",
+  RED = "red",
+  GREEN = "green",
+  BLUE = "blue",
+  ALPHA = "alpha",
+  PALETTE = "palette",
+  CYAN = "cyan",
+  MAGENTA = "magenta",
+  YELLOW = "yellow",
+  BLACK = "black",
+  Y = "Y",
+  Cb = "Cb",
+  Cr = "Cr",
+}
+
+export function inferColorInterpretation({
+  count,
+  photometric,
+  extraSamples,
+}: {
+  count: number;
+  photometric: Photometric | null;
+  extraSamples: ExtraSample[] | null;
+}): ColorInterp[] {
+  switch (photometric) {
+    case null:
+      return Array<ColorInterp>(count).fill(ColorInterp.UNDEFINED);
+
+    case Photometric.MinIsBlack:
+      return Array<ColorInterp>(count).fill(ColorInterp.GRAY);
+
+    case Photometric.Rgb: {
+      if (count < 3) {
+        throw new Error(
+          "RGB photometric interpretation with fewer than 3 bands is not supported.",
+        );
+      }
+      if (count === 3) {
+        return [ColorInterp.RED, ColorInterp.GREEN, ColorInterp.BLUE];
+      }
+      // count >= 4: map extra samples
+      const extras = (extraSamples ?? []).map((sample) =>
+        sample === ExtraSample.UnassociatedAlpha ? ColorInterp.ALPHA : ColorInterp.UNDEFINED,
+      );
+      return [ColorInterp.RED, ColorInterp.GREEN, ColorInterp.BLUE, ...extras];
+    }
+
+    case Photometric.Palette:
+      return [ColorInterp.PALETTE];
+
+    case Photometric.Separated:
+      return [ColorInterp.CYAN, ColorInterp.MAGENTA, ColorInterp.YELLOW, ColorInterp.BLACK];
+
+    case Photometric.Ycbcr:
+      return [ColorInterp.Y, ColorInterp.Cb, ColorInterp.Cr];
+
+    default:
+      throw new Error(
+        `Color interpretation not implemented for photometric: ${photometric}`,
+      );
+  }
+}

packages/geotiff/src/geotiff.ts

@@ -1,4 +1,4 @@
 import { SourceCache, SourceChunk } from "@chunkd/middleware";
 import { SourceView } from "@chunkd/source";
 import { SourceHttp } from "@chunkd/source-http";
 import { SourceMemory } from "@chunkd/source-memory";
@@ -10,6 +10,8 @@
 import { fetchTile } from "./fetch.js";
 import type { BandStatistics, GDALMetadata } from "./gdal-metadata.js";
 import { parseGDALMetadata } from "./gdal-metadata.js";
+import type { ColorInterp } from "./colorinterp.js";
+import { inferColorInterpretation } from "./colorinterp.js";
 import type { CachedTags, GeoKeyDirectory } from "./ifd.js";
 import { extractGeoKeyDirectory, prefetchTags } from "./ifd.js";
 import { Overview } from "./overview.js";
@@ -330,6 +332,15 @@
     return this.image.value(TiffTag.SamplesPerPixel) ?? 1;
   }
 
+  /** The color interpretation of each band in index order. */
+  get colorInterp(): ColorInterp[] {
+    return inferColorInterpretation({
+      count: this.count,
+      photometric: this.cachedTags.photometric,
+      extraSamples: this.cachedTags.extraSamples,
+    });
+  }
+
   /** Bounding box [minX, minY, maxX, maxY] in the CRS. */
   get bbox(): [number, number, number, number] {
     return this.image.bbox;

packages/geotiff/src/ifd.ts

@@ -1,11 +1,28 @@
 import type { TiffImage, TiffTagGeoType, TiffTagType } from "@cogeotiff/core";
 import { Predictor, SampleFormat, TiffTag, TiffTagGeo } from "@cogeotiff/core";
 
+/**
+ * Description of extra components.
+ *
+ * Specifies that each pixel has N extra components whose interpretation is
+ * defined by one of the values listed below. When this field is used, the
+ * SamplesPerPixel field has a value greater than the PhotometricInterpretation
+ * field suggests.
+ *
+ * @see https://web.archive.org/web/20240329145321/https://www.awaresystems.be/imaging/tiff/tifftags/extrasamples.html
+ */
+export enum ExtraSample {
+  Unspecified = 0,
+  AssociatedAlpha = 1,
+  UnassociatedAlpha = 2,
+}
+
 /** Subset of TIFF tags that we pre-fetch for easier visualization. */
 export interface CachedTags {
   bitsPerSample: Uint16Array;
   colorMap?: Uint16Array; // TiffTagType[TiffTag.ColorMap];
   compression: TiffTagType[TiffTag.Compression];
+  extraSamples: [ExtraSample] | null;
   gdalMetadata: TiffTagType[TiffTag.GdalMetadata] | null;
   lercParameters: TiffTagType[TiffTag.LercParameters] | null;
   modelTiepoint: TiffTagType[TiffTag.ModelTiePoint] | null;
@@ -33,6 +50,7 @@ export async function prefetchTags(image: TiffImage): Promise<CachedTags> {
   const [
     bitsPerSample,
     colorMap,
+    extraSamples,
     gdalNoData,
     gdalMetadata,
     lercParameters,
@@ -49,6 +67,7 @@ export async function prefetchTags(image: TiffImage): Promise<CachedTags> {
   ] = await Promise.all([
     image.fetch(TiffTag.BitsPerSample),
     image.fetch(TiffTag.ColorMap),
+    image.fetch(TiffTag.ExtraSamples),
     image.fetch(TiffTag.GdalNoData),
     image.fetch(TiffTag.GdalMetadata),
     image.fetch(TiffTag.LercParameters),
@@ -91,6 +110,7 @@ export async function prefetchTags(image: TiffImage): Promise<CachedTags> {
     bitsPerSample: new Uint16Array(bitsPerSample),
     colorMap: colorMap ? new Uint16Array(colorMap as number[]) : undefined,
     compression,
+    extraSamples: (extraSamples as [ExtraSample] | null) ?? null,
     gdalMetadata,
     lercParameters,
     modelTiepoint,