From 1d0abcaee8eb7843b696ecc025ad1de3446a1681 Mon Sep 17 00:00:00 2001
From: Jeff Schiller <codedread@gmail.com>
Date: Tue, 16 Jan 2024 08:19:58 -0800
Subject: [PATCH] PngParser: Handle gAMA chunk

---
 image/parsers/png.js               |  32 ++++++++++++++++++++++++++++-
 tests/image-parsers-png.spec.js    |  10 +++++++++
 tests/image-testfiles/g05n3p04.png | Bin 0 -> 206 bytes
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 tests/image-testfiles/g05n3p04.png

diff --git a/image/parsers/png.js b/image/parsers/png.js
index 36883b7..453b398 100644
--- a/image/parsers/png.js
+++ b/image/parsers/png.js
@@ -14,12 +14,14 @@ import { ByteStream } from '../../io/bytestream.js';
 // https://en.wikipedia.org/wiki/PNG#File_format
 // https://www.w3.org/TR/2003/REC-PNG-20031110
 
+// let DEBUG = true;
 let DEBUG = false;
 const SIG = new Uint8Array([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]);
 
 /** @enum {string} */
 export const PngParseEventType = {
   IHDR: 'image_header',
+  gAMA: 'image_gamma',
   PLTE: 'palette',
   IDAT: 'image_data',
 };
@@ -59,6 +61,15 @@ export class PngImageHeaderEvent extends Event {
   }
 }
 
+export class PngImageGammaEvent extends Event {
+  /** @param {number} */
+  constructor(gamma) {
+    super(PngParseEventType.gAMA);
+    /** @type {number} */
+    this.gamma = gamma;
+  }
+}
+
 /**
  * @typedef PngColor
  * @property {number} red
@@ -132,6 +143,16 @@ export class PngParser extends EventTarget {
     return this;
   }
 
+  /**
+   * Type-safe way to bind a listener for a PngImageGammaEvent.
+   * @param {function(PngImageGammaEvent): void} listener
+   * @returns {PngParser} for chaining
+   */
+  onGamma(listener) {
+    super.addEventListener(PngParseEventType.gAMA, listener);
+    return this;
+  }
+
   /**
    * Type-safe way to bind a listener for a PngPaletteEvent.
    * @param {function(PngPaletteEvent): void} listener
@@ -204,6 +225,12 @@ export class PngParser extends EventTarget {
           this.dispatchEvent(new PngImageHeaderEvent(header));
           break;
 
+        // https://www.w3.org/TR/2003/REC-PNG-20031110/#11gAMA
+        case 'gAMA':
+          if (length !== 4) throw `Bad length for gAMA: ${length}`;
+          this.dispatchEvent(new PngImageGammaEvent(chStream.readNumber(4)));
+          break;
+
         // https://www.w3.org/TR/2003/REC-PNG-20031110/#11PLTE
         case 'PLTE':
           if (this.colorType === undefined) throw `PLTE before IHDR`;
@@ -282,8 +309,11 @@ async function main() {
     parser.onImageHeader(evt => {
       // console.dir(evt.imageHeader);
     });
+    parser.onGamma(evt => {
+      // console.dir(evt.imageGamma);
+    });
     parser.onPalette(evt => {
-      console.dir(evt.palette);
+      // console.dir(evt.palette);
     });
     parser.onImageData(evt => {
       // console.dir(evt);
diff --git a/tests/image-parsers-png.spec.js b/tests/image-parsers-png.spec.js
index 68714c4..ca2cd55 100644
--- a/tests/image-parsers-png.spec.js
+++ b/tests/image-parsers-png.spec.js
@@ -5,6 +5,7 @@ import { PngColorType, PngInterlaceMethod, PngParser } from '../image/parsers/pn
 
 /** @typedef {import('../image/parsers/png.js').PngImageHeader} PngImageHeader */
 /** @typedef {import('../image/parsers/png.js').PngImageData} PngImageData */
+/** @typedef {import('../image/parsers/png.js').PngImageGamma} PngImageGamma */
 /** @typedef {import('../image/parsers/png.js').PngPalette} PngPalette */
 
 function getPngParser(fileName) {
@@ -47,6 +48,15 @@ describe('bitjs.image.parsers.PngParser', () => {
     });
   });
 
+  it('extracts gAMA', async () => {
+    /** @type {number} */
+    let gamma;
+    await getPngParser('tests/image-testfiles/g05n3p04.png')
+        .onGamma(evt => gamma = evt.gamma)
+        .start();
+    expect(gamma).equals(55000);
+  });
+
   it('extracts PLTE', async () => {
     /** @type {PngPalette} */
     let palette;
diff --git a/tests/image-testfiles/g05n3p04.png b/tests/image-testfiles/g05n3p04.png
new file mode 100644
index 0000000000000000000000000000000000000000..9619930585eb3798db54058d41c09f6cd195c723
GIT binary patch
literal 206
zcmeAS@N?(olHy`uVBq!ia0vp^3LwnF3?v&v(vJfvmUKs7M+Sy#H?H_c7y<cm0X`wF
zK$_wI|1)P8{-62Jux{OdhX38&Kmi~Cvi=u8Qkeu)5bf#W7*a7O`2|B$fI<NylcPd{
zgIEFs<F6F~OieQ#7{VKM9Na}S9TIq03PevZO<8GRP*#}W7<Mq>&7nsP&a50$ri)KG
u9IC*rureVboiWQXC@_w%oP86+Of7~h92M4HZx@7u9OCKf=d#Wzp$PyhYDC`v

literal 0
HcmV?d00001