Hi so I'm trying to convert an image to sketch-like-image before uploading it to the server, the uploading part is not the problem, the conversion of image to sketch-like-image is. I failed to search a js library that will help me achieve this, and then I found this https://www.freecodecamp.org/news/sketchify-turn-any-image-into-a-pencil-sketch-with-10-lines-of-code-cf67fa4f68ce sample code in python
then tried to recreate it using CSS only and I got it correctly using the CSS code below
filter: grayscale(100%) invert(100%) blur(5px);
mix-blend-mode: color-dodge;
Then after that I tried to recreate it in Vanilla Javascript using CANVAS API because I needed the image to be uploaded in the server that looks like a sketch-like-image, but got stuck in the process here are the stages of the conversion I'm doing see image below
I got stuck in the stage 4, I can't proceed with the stage 5, which is globalCompositeOperation = 'color-dodge';
when color-dodge applied to CANVAS API, to remove the blur and make it look like an sketch-image
grayscale(100%)
working in javascript CANVAS APIinvert(100%)
working in javascript CANVAS APIblur(5px)
working in javascript CANVAS APIglobalCompositeOperation = 'color-dodge'
which is equivalent of CSS' mix-blend-mode: color-dodge;
I think? I'm not sure but I assumed it is. not working in javascript CANVAS APIand here's my Javascript code below
let img = document.createElement('img');
let canvas = document.createElement('canvas');
let ctx = canvas.getContext('2d');
ctx.filter = 'grayscale(100%) invert(100%) blur(5px)'; // stages 2,3,4 is working
ctx.globalCompositeOperation = 'color-dodge'; // stage 5 not working
ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
Ok so I think that's a lot so here's a snippet of it for you guys to test it out. https://codepen.io/ohyeahhu/pen/MWQRweP
also if you guys know a JS library or tools that might help me achieve this feat, I'm very open to any suggestions.
note: only in javascript or any js library
Posting it here for others, the solution to this is I need to generate a black & white and blur canvas/img separately and then merge them using CANVAS API.
So to summarize the code below, I created 2 function. filter
and generateSketch
, filter
purpose is to add filter to the canvas element and generateSketch
is to merge two canvas (black & white and blur) into one to create a sketch like image.
HTML
<div class="col-sm-6">
<h1 class="text-center">Converted using JAVASCRIPT</h1>
<div class="row">
<div class="col-sm-6">
<img src="https://i.postimg.cc/Wb5CcD8L/corgi2.jpg" id="raw-img" class="d-block w-100">
</div>
<div class="col-sm-6" id="result">
</div>
</div>
</div>
Javascript
window.addEventListener('DOMContentLoaded', async (event) => {
// add filters to canvas element
const filter = (bmp, filters="") => {
let canvas = Object.assign(document.createElement('canvas'), { width: bmp.width, height: bmp.height });
let ctx = canvas.getContext('2d');
ctx.filter = filters;
ctx.drawImage(bmp, 0, 0);
return canvas;
}
// merge two canvas into one to generate sketch like image
const generateSketch = (bnw, blur) => {
let canvas = document.createElement('canvas');
canvas.width = bnw.width;
canvas.height = bnw.height;
canvas.__skipFilterPatch = true; // davidenke/context-filter-polyfill fix for safari ios devices
let ctx = canvas.getContext('2d');
ctx.drawImage(bnw, 0, 0, canvas.width, canvas.height);
ctx.globalCompositeOperation = 'color-dodge';
ctx.drawImage(blur, 0, 0, canvas.width, canvas.height);
return canvas;
}
let rawImg = document.getElementById('raw-img');
// first: step create bitmap from the `rawImg`
let bmp = await createImageBitmap(rawImg);
// second: generate a black & white and blur canvas using filter()
let bnw = filter(bmp, "grayscale(1)");
let blur = filter(bmp, "grayscale(1) invert(1) blur(5px)");
// third: merge / combine `bnw` and `blur` canvas
let sketchImg = generateSketch(bnw, blur);
// display output
let resultDiv = document.getElementById('result');
resultDiv.prepend(sketchImg);
});
you can check it on my codepen for the working sample https://codepen.io/ohyeahhu/pen/MWQRweP.
note: I also used https://github.com/davidenke/context-filter-polyfill to fix the compatibility issue on Safari IOS devices.
This is also related to this CanvasRenderingContext2D.globalCompositeOperation is not working on safari