The plugin could have the feature to create PNG-8 greyscaled pictures

src/browser/browser.ts

@@ -6,6 +6,8 @@ import * as path from 'path';
 import * as fs from 'fs';
 import * as promClient from 'prom-client';
 import * as Jimp from 'jimp';
+import configure from "@jimp/custom";
+import png from "@jimp/png";
 import { Logger } from '../logger';
 import { RenderingConfig } from '../config/rendering';
 import { ImageRenderOptions, RenderOptions } from '../types';
@@ -415,6 +417,22 @@ export class Browser {
       });
     }
 
+    if (options.greyScaleImage && !isPDF) {
+      await this.performStep('greyScale', options.url, signal, async () => {
+        const jimp = configure({ types: [png] }, Jimp);
+        const greyScaled = `${options.filePath}_${Date.now()}_greyscaled.png`;
+
+        const file = await jimp.read(options.filePath);
+        await file
+          .greyscale()
+          .deflateStrategy(0)
+          .colorType(0)
+          .writeAsync(greyScaled);
+
+        fs.renameSync(greyScaled, options.filePath);
+      });        
+    } 
+
     return { filePath: options.filePath };
   }
 

src/service/http-server.ts

@@ -200,6 +200,7 @@ export class HttpServer {
       timezone: req.query.timezone,
       encoding: req.query.encoding,
       deviceScaleFactor: req.query.deviceScaleFactor,
+      greyScaleImage: req.query.greyScaleImage,
       headers: headers,
     };
 

src/types.ts

@@ -24,4 +24,5 @@ export interface ImageRenderOptions extends RenderOptions {
   // Runtime options derived from the input
   fullPageImage?: boolean;
   scaleImage?: number;
+  greyScaleImage?: boolean;
 }