add option to change initial quality

Author: Donaldcwl

README.md

@@ -51,7 +51,8 @@ const options = {
   maxIteration: number,       // optional, max number of iteration to compress the image (default: 10)
   exifOrientation: number,    // optional, see https://stackoverflow.com/a/32490603/10395024
   onProgress: Function,       // optional, a function takes one progress argument (percentage from 0 to 100) 
-  fileType: string            // optional, fileType override
+  fileType: string,           // optional, fileType override
+  initialQuality: number      // optional, initial quality value during compression 
 }
 
 imageCompression(file: File, options): Promise<File | Blob>

lib/image-compression.js

@@ -13,13 +13,15 @@ import {
  * Compress an image file.
  *
  * @param {File} file
- * @param {Object} options - { maxSizeMB=Number.POSITIVE_INFINITY, maxWidthOrHeight, useWebWorker=false, maxIteration = 10, exifOrientation, fileType }
+ * @param {Object} options
  * @param {number} [options.maxSizeMB=Number.POSITIVE_INFINITY]
  * @param {number} [options.maxWidthOrHeight=undefined]
+ * @param {boolean} [options.useWebWorker=false]
  * @param {number} [options.maxIteration=10]
  * @param {number} [options.exifOrientation] - default to be the exif orientation from the image file
  * @param {Function} [options.onProgress] - a function takes one progress argument (progress from 0 to 100)
  * @param {string} [options.fileType] - default to be the original mime type from the image file
+ * @param {number} [options.initialQuality=1.0]
  * @returns {Promise<File | Blob>}
  */
 export default async function compress (file, options) {
@@ -57,7 +59,7 @@ export default async function compress (file, options) {
   const orientationFixedCanvas = (await isAutoOrientationInBrowser) ? maxWidthOrHeightFixedCanvas : followExifOrientation(maxWidthOrHeightFixedCanvas, options.exifOrientation)
   incProgress()
 
-  let quality = 1
+  let quality = options.initialQuality || 1.0
 
   let tempFile = await canvasToFile(orientationFixedCanvas, options.fileType || file.type, file.name, file.lastModified, quality)
   incProgress()

lib/index.d.ts

@@ -18,6 +18,8 @@ interface Options {
     onProgress?: (progress: number) => void;
     /** Default to be the original mime type from the image file */
     fileType?: string;
+    /** @default 1.0 */
+    initialQuality?: number;
 }
 
 declare function imageCompression(image: File | Blob, options: Options): Promise<File | Blob>;