feat: add 1-bit image decoder

Author: EscapedGibbon

src/BMPDecoder.ts

@@ -0,0 +1,60 @@
+import { IOBuffer } from 'iobuffer';
+
+import type { ImageCodec } from './BMPEncoder';
+
+export default class BMPDecoder {
+  bufferData: IOBuffer;
+  pixelDataOffset: number;
+  width: number;
+  height: number;
+  bitDepth: number;
+
+  constructor(bufferData: Buffer) {
+    this.bufferData = new IOBuffer(bufferData);
+    const formatCheck = this.bufferData.readBytes(2);
+    if (formatCheck[0] !== 0x42 && formatCheck[1] !== 0x4d) {
+      throw new Error(
+        'This is not a BMP image or the encoding is not correct.'
+      );
+    }
+    this.pixelDataOffset = this.bufferData.skip(8).readUint32();
+    this.width = this.bufferData.skip(4).readUint32();
+    this.height = this.bufferData.readUint32();
+    this.bitDepth = this.bufferData.seek(28).readUint16();
+    if (this.bitDepth !== 1) {
+      throw new Error('only bitDepth of 1 is supported');
+    }
+  }
+
+  decode(): ImageCodec {
+    this.bufferData.seek(this.pixelDataOffset);
+    const data = new Uint8Array(this.height * this.width * this.bitDepth);
+    this.bufferData.setBigEndian();
+
+    let currentNumber = 0;
+
+    for (let row = 0; row < this.height; row++) {
+      for (let col = 0; col < this.width; col++) {
+        const bitIndex = col % 32;
+        if (bitIndex === 0) {
+          currentNumber = this.bufferData.readUint32();
+        }
+
+        if (currentNumber & (1 << (31 - bitIndex))) {
+          data[(this.height - row - 1) * this.width + col] = 1;
+        }
+      }
+    }
+
+    const channels = Math.ceil(this.bitDepth / 8);
+    const components = channels % 2 === 0 ? channels - 1 : channels;
+    return {
+      width: this.width,
+      height: this.height,
+      bitDepth: this.bitDepth,
+      channels,
+      components,
+      data,
+    };
+  }
+}

src/BMPEncoder.ts

@@ -2,7 +2,7 @@ import { IOBuffer } from 'iobuffer';
 
 import { BITMAPV5HEADER } from './constants';
 
-export interface DataToEncode {
+export interface ImageCodec {
   /**
    * Image bit depth.
    */
@@ -41,7 +41,7 @@ export default class BMPEncoder extends IOBuffer {
   channels: number;
   components: number;
   encoded: IOBuffer = new IOBuffer();
-  constructor(data: DataToEncode) {
+  constructor(data: ImageCodec) {
     if (data.bitDepth !== 1) {
       throw new Error('Only bitDepth of 1 is supported');
     }