ngx-image2dataurl

An Angular component which reads the dataURL and optionally resizes the selected input file image.

Demo

Install

npm install ngx-image2dataurl --save

Usage

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';
import { ImageToDataUrlModule } from "ngx-image2dataurl";

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    ImageToDataUrlModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

import { Component } from '@angular/core';
import { Options, ImageResult } from "ngx-image2dataurl";

@Component({
  selector: 'app-root',
  template: `
    <img [src]="src" *ngIf="src"><br>
    <input type="file" [imageToDataUrl]="options"
      (imageSelected)="selected($event)">
  `
})
export class AppComponent {
  src: string = null;
  options: Options = {
    resize: {
      maxHeight: 128,
      maxWidth: 128
    },
    allowedExtensions: ['JPG', 'PnG']
  };

  selected(imageResult: ImageResult) {
    if (imageResult.error) alert(imageResult.error);
    this.src = imageResult.resized
      && imageResult.resized.dataURL
      || imageResult.dataURL;
  }
}

API

selector: input[type=file][imageToDataUrl]

event: (imageSelected)

event fired (async) when the file input changes and the image's dataURL is calculated and the image is resized.

export interface ImageResult {
  file: File;
  url: string;
  dataURL?: string;
  error?: any;
  resized?: {
      dataURL: string;
      type: string;
  }
}

If any error happens, the error field is set with an error message. (e.g. 'Extension Not Allowed' or 'Image processing error') If the error happens during resizing, file, url (objectURL) of the original image is still set.

property: [imageToDataUrl] - options

export interface ResizeOptions {
  maxHeight?: number;
  maxWidth?: number;
  quality?: number;
  type?: string;
  bgColor?: string;
}

export interface Options {
  resize?: ResizeOptions;
  allowedExtensions?: string[];
}

• resize: default undefined
• resize.maxHeight
• resize.maxWidth
• resize.quality: default: 0.7
• resize.type: default: as the original image
• resize.bgColor: default: undefined
• allowedExtensions: default: undefined

Resize algorithm ensures, that the resized image can fit into the specified resize.maxHeight x resize.maxWidth size. bgColor is an optional parameter to force a certain background color when 'flattening' transparent images (as the default is black and this may be undesirable).

Allowed extensions array (e.g. ['jpg', 'jpeg', 'png']; case insensitive): if specified and an input file has different extension the (imageSelected) event is fired with the error field set to 'Extension Not Allowed'. dataURL and resize not calculated at all.

Multi-Injector IMAGE_FILE_PROCESSOR as ImageFileProcessor

interface ImageFileProcessor {
  process(dateURL: string): Promise<string>;
}

This interface allows to plugin-in any image processing logic which works on the opened file's dataURL and should return a promise of the processed image's dataURL. You can provide multiple image processors which are changed: ones input is the output of the previous processor.

The initial idea of this feature comes from a request and PR to support automatic EXIF rotation of images. Since I didn't want to package any EXIF processing dependency with this library, I decided to let the users plug-in their own solution. See an old PR from the legacy repo to get some idea how to handle.

There are two utility function you can use:

createImageFromDataUrl(dataURL: string): Promise<HTMLImageElement>: creates an image from dataURL which can be used to draw into a canvas.

getImageTypeFromDataUrl(dataURL): Promise<HTMLImageElement>: determines the MIME type of the image represented by the dataURL. Can be used in Canvas.toDataURL(type) method.

Example

// define the processor in the providers section
providers: [
  {
    provide: IMAGE_FILE_PROCESSOR,
    useClass: RotateImageFileProcessor,
    multi: true
  }
]

import { 
  createImageFromDataUrl, getImageTypeFromDataUrl, ImageFileProcessor
} from "ngx-image2dataurl";

// the processor
export class RotateImageFileProcessor implements ImageFileProcessor {
  async process(dataURL: string): Promise<string> {
    const canvas = document.createElement('canvas');
    const image = await createImageFromDataUrl(dataURL);
    canvas.width = image.height;
    canvas.height = image.width;
    const ctx = canvas.getContext("2d");
    ctx.save();
    ctx.translate(canvas.width / 2, canvas.height / 2);
    ctx.rotate(Math.PI / 2);
    ctx.drawImage(image, -image.width / 2, -image.height / 2);
    ctx.restore();
    return canvas.toDataURL(getImageTypeFromDataUrl(dataURL));
  }
}