README.md

ng2-img-max

Angular 2 and beyond module to resize images down to a certain width and height or to reduce the quality to fit a certain maximal filesize - all in the browser.

This means, the huge image that the user may select will never even need to be uploaded to the server.

Demo

A simple demo is available on stackblitz: https://stackblitz.com/edit/angular-ivy-hnhy6v

Browser support

This module is supported by all major browsers recent versions (IE 10+).

Make sure to include the following polyfill for HtmlCanvasElement.toBlob(): https://www.npmjs.com/package/blueimp-canvas-to-blob

$ npm install blueimp-canvas-to-blob

Make sure to check out ng2-img-tools for further image manipulation such as resizing to an exact size (e.g. to create thumbnails) or image cropping as seen in the demo.

Install

$ npm install ng2-img-max

Import the module

Only needed for Angular versions prior to 13

// app.module.ts
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { Ng2ImgMaxModule } from 'ng2-img-max'; // <-- import the module
import { MyComponent } from './my.component';

@NgModule({
    imports: [BrowserModule,
              Ng2ImgMaxModule // <-- include it in your app module
             ],
    declarations: [MyComponent],  
    bootstrap: [MyComponent]
})
export class MyAppModule {}

Usage

import { Ng2ImgMaxService } from 'ng2-img-max';
[...]
    constructor(private ng2ImgMaxService: Ng2ImgMaxService) {
        this.ng2ImgMaxService.resize([someImage], 2000, 1000).subscribe((result)=>{
        });
    }
}

Methods

Maximal filesize

IMPORTANT: Catch error cases

When using the compression methods you should make sure to catch the error cases. If an error happens, you will receive an object with the following properties: compressedFile:File, reason: string and error:string

Possible errors are:
INVALID_EXTENSION: File provided is neither of type jpg nor of type png). The compressedFile is the original file.
PNG_WITH_ALPHA: File provided is a png image which uses the alpha channel. No compression possible unless ignoreAlpha is set to true. The compressedFile is the original file.
MAX_STEPS_EXCEEDED: Could not find the correct compression quality in 15 steps - abort. This should rarely to never at all happen. The compressedFile is the result of step 15 of the compression.
FILE_BIGGER_THAN_INITIAL_FILE: This should actually never happen, just a precaution. The compressedFile is the original file.
UNABLE_TO_COMPRESS_ENOUGH: Could not compress image enough to fit the maximal file size limit. The compressedFile is a compression as close as it can get.

Example code catch errors:

this.ng2ImgMaxService.resize([someImage], 2000, 1000).subscribe(result => {
   //all good, result is a file
   console.info(result);
}, error => {
   //something went wrong 
   //use result.compressedFile or handle specific error cases individually
});

compress(files: File[], maxSizeInMB: number, ignoreAlpha: boolean = false, logExecutionTime: boolean = false): Observable<any>

Method to compress an image. This reduces the quality of an image down until it fits a certain fileSize which is given as maxSizeInMB. Set ignoreAlpha to true if you want to ignore the alpha channel for png images and compress them nonetheless (not recommended - the alpha channel will be lost and the resulting image might differ from the original image). Returns an observable that for every file given, onNext receives either a File when everything went as planned or an error Object if something went wrong.

compressImage

Same as above just that it takes in only one file instead of a whole array of files.

Maximal width / height

resize(files: File[], maxWidth: number, maxHeight: number, logExecutionTime: boolean = false): Observable<any>

Method to resize files if necessary down to a certain maximal width or maximal height in px. If you want only one limit just set the other max to 10.000: for example resize([myfile1,myfile2],2000,10000).subscribe([...]

resizeImage

Same as above just that it takes in only one file instead of a whole array of files.

Get EXIF oriented image

getEXIFOrientedImage(image:HTMLImageElement): Promise<HTMLImageElement>

Method that returns an image respecting the EXIF orientation data.

Contribute

Due to the lack of other algorithms that also reduce the filesize of an image by reducing the quality until it fits a certain limit, help to find the best possible algorithm to do so is much appreciated. The current algorithm can be found here: https://github.com/bergben/ng2-img-max/blob/master/src/img-max-size.service.ts.

Limitations

Although the resizing functions do use web workers to do the heavy work, this is not possible for the compression methods. The reasons for this are that a web worker does not have access to the DOM and can therefor not create a new HtmlCanvasElement. Neither can it be passed as a parameter to the web worker, as a web worker can only receive serializable data, which only be the ImageData but that can only be turned into a 2DCanvasContext, not a HtmlCanvasElement itself without the DOM.