HTML5 Canvas Contrast filter Image Tutorial

To apply filter to an Konva.Node, we have to cache it first with cache() function. Then apply filter with filters() function.

To change contrast of an image with Konva, we can use the Konva.Filters.Contrast.

Instructions: Slide the control to change contrast value.

For all available filters go to Filters Documentation.

Vanilla

import Konva from 'konva';

const width = window.innerWidth;
const height = window.innerHeight;

const stage = new Konva.Stage({
  container: 'container',
  width: width,
  height: height,
});

const layer = new Konva.Layer();
stage.add(layer);

const imageObj = new Image();
imageObj.onload = () => {
  const image = new Konva.Image({
    x: 50,
    y: 50,
    image: imageObj,
    draggable: true,
  });

  layer.add(image);

  image.cache();
  image.filters([Konva.Filters.Contrast]);
  image.contrast(30);

  const slider = document.createElement('input');
  slider.type = 'range';
  slider.min = '-100';
  slider.max = '100';
  slider.value = image.contrast();

  slider.style.position = 'absolute';
  slider.style.top = '20px';
  slider.style.left = '20px';

  slider.addEventListener('input', (e) => {
    const value = parseInt(e.target.value);
    image.contrast(value);
    layer.batchDraw();
  });

  document.body.appendChild(slider);
};

imageObj.src = 'https://new.konvajs.org/assets/lion.png';
imageObj.crossOrigin = 'anonymous';

Open Sandbox

React

import { Stage, Layer, Image } from 'react-konva';
import { useState, useEffect, useRef } from 'react';
import useImage from 'use-image';

const App = () => {
  const [contrast, setContrast] = useState(30);
  const [image] = useImage('https://new.konvajs.org/assets/lion.png', 'anonymous');
  const imageRef = useRef(null);

  useEffect(() => {
    if (image) {
      imageRef.current.cache();
    }
  }, [image]);

  return (
    <>
      <Stage width={window.innerWidth} height={window.innerHeight}>
        <Layer>
          <Image
            ref={imageRef}
            x={50}
            y={50}
            image={image}
            draggable
            filters={[Konva.Filters.Contrast]}
            contrast={contrast}
          />
        </Layer>
      </Stage>
      <input
        type="range"
        min="-100"
        max="100"
        value={contrast}
        onChange={(e) => setContrast(parseInt(e.target.value))}
        style={{ position: 'absolute', top: '20px', left: '20px' }}
      />
    </>
  );
};

Open Sandbox

Vue

<template>
  <div>
    <v-stage :config="stageSize">
      <v-layer>
        <v-image
          ref="imageNode"
          :config="{
            x: 50,
            y: 50,
            image: image,
            draggable: true,
            filters: [Konva.Filters.Contrast],
            contrast: contrast,
          }"
        />
      </v-layer>
    </v-stage>
    <input
      type="range"
      min="-100"
      max="100"
      :value="contrast"
      @input="handleSlider"
      style="position: absolute; top: 20px; left: 20px"
    />
  </div>
</template>

<script setup>
import { ref, watch, nextTick } from 'vue';
import { useImage } from 'vue-konva';
import Konva from 'konva';

const stageSize = {
  width: window.innerWidth,
  height: window.innerHeight,
};

const contrast = ref(30);
const imageNode = ref(null);
const [image] = useImage('https://new.konvajs.org/assets/lion.png', 'anonymous');

watch(image, async (newImage) => {
  if (newImage) {
    await nextTick();
    imageNode.value.getNode().cache();
  }
});

const handleSlider = (e) => {
  contrast.value = parseInt(e.target.value);
};
</script>

Open Sandbox