Examples

Load a jpeg, resize it, and save it as a png

import 'dart:io' as Io;
import 'package:image/image.dart';
void main() {
  // Read a jpeg image from file.
  Image image = decodeJpg(new Io.File('test.jpg').readAsBytesSync());

  // Resize the image to a 120x? thumbnail (maintaining the aspect ratio).
  Image thumbnail = copyResize(image, 120);

  // Save the thumbnail as a PNG.
  new Io.File('out/thumbnail-test.png')
        ..writeAsBytesSync(encodePng(thumbnail));
}

Convert all WebP images on a page to PNG so that browsers lacking WebP can view them

import 'dart:html' as Html;
import 'package:crypto/crypto.dart';
import 'package:image/image.dart';

void main() {
  var images = Html.querySelectorAll('img');

  for (var img in images) {
    if (img.src.toLowerCase().endsWith('.webp')) {
      // Since the browser might not have decoded the image, use an HttpRequest to get the image
      // data, convert it to binary, decode the WebP using the image library, re-encode it to
      // PNG, base64 encode the PNG, and replace the img src with a data URL.
      var req = new Html.HttpRequest();
      req.open('GET', img.src);
      req.overrideMimeType('text\/plain; charset=x-user-defined');
      req.onLoadEnd.listen((e) {
        if (req.status == 200) {
          // convert the responseText to a byte list.
          var bytes = req.responseText.split('').map((e){
            return new String.fromCharCode(e.codeUnitAt(0) & 0xff);
          }).join('').codeUnits;

          var image = decodeWebP(bytes);
          var png = encodePng(image);

          var png64 = CryptoUtils.bytesToBase64(png);
          img.src = 'data:image/png;base64,${png64}';
        }
      });
      req.send('');
    }
  }
}

Read and Write an Image from/to a Canvas element

import 'dart:html' as Html;
import 'package:image/image.dart';

// The returned Image will be accessing the data of the canvas directly, so any changes you
// make to the pixels of Image will apply to the canvas.
Image getImageFromCanvas(Html.CanvasElement canvas) {
  var imageData = c.context2D.getImageData(0, 0, canvas.width, canvas.height);
  return new Image.fromBytes(canvas.width, canvas.height, imageData.data);
}

void setCanvasImage(Html.CanvasElement canvas, Image image) {
  var imageData = canvas.context2D.createImageData(image.width, image.height);
  imageData.data.setRange(0, imageData.data.length, image.getBytes());
  // Draw the buffer onto the canvas.
  canvas.context2D.clearRect(0, 0, canvas.width, canvas.height);
  canvas.context2D.putImageData(imageData, 0, 0);
}

Create an image, draw some text, save it as a png

import 'dart:io' as Io;
import 'package:image/image.dart';
void main() {
  // Create an image
  Image image = new Image(320, 240);
  
  // Fill it with a solid color (blue)
  fill(image, getColor(0, 0, 255));
  
  // Draw some text using 24pt arial font
  drawString(image, arial_24, 0, 0, 'Hello World');
  
  // Draw a line
  drawLine(image, 0, 0, 320, 240, getColor(255, 0, 0), thickness: 3);
  
  // Blur the image
  gaussianBlur(image, 10);
  
  // Generate a PNG
  List<int> png = encodePng(image);
  
  // Save it to disk
  new Io.File('test.png')
        ..writeAsBytesSync(png);
}

Map the grayscale of the image to its alpha channel

Image grayscaleAlpha(Image image) {
    // Make sure the image is in RGBA format.
    image.format = Image.RGBA;
    // Map the LUMINANCE (grayscale) of the image to the alpha channel.
    return remapColors(image, alpha: LUMINANCE);
}

Save the frames from a WebP animation to PNG files

import 'dart:io' as Io;
import 'package:image/image.dart';
void main() {
  List<int> bytes = new Io.File('BladeRunner.webp').readAsBytesSync();
  Animation anim = new WebPDecoder().decodeAnimation(bytes);
  for (int i = 0; i < anim.numFrames; ++i) {
    AnimationFrame frame = anim[i];
    new Io.File('BladeRunner_$i.png')
          ..writeAsBytesSync(encodePng(frame.image));
  }
}

Load a directory of images, auto-trim the first image, and apply the trim to all subsequent images.

import 'dart:io' as Io;
import 'package:image/image.dart';
void main(List<String> argv) {
  String path = argv[0];
  Io.Directory dir = new Io.Directory(path);
  List files = dir.listSync();
  List<int> trimRect;
  for (var f in files) {
    if (f is! Io.File) {
      continue;
    }
    List<int> bytes = f.readBytesSync();
    Image image = decodeNamedImage(bytes, f.path);
    if (image == null) {
      continue;
    }
    if (trimRect == null) {
      trimRect = findTrim(image, mode: TRIM_TRANSPARENT);
    }
    Image trimmed = copyCrop(image, trimRect[0], trimRect[1], trimRect[2], trimRect[3]);
    String name = f.path.split(new RegExp(r'(/|\\)')).last;
    new Io.File('$path/trimmed-$name').writeBytesSync(encodeNamedImage(image, f.path));
  }
}