Draw image from pixel array on canvas with putImageData

javascript arrays canvas pixel putimagedata
Elias Pedersen picture Elias Pedersen · Apr 9, 2013 · Viewed 17.4k times · Source

I am working on a project that can encrypt an image and redraw the decrypted image on canvas. As I am still pretty new to coding and programming, I am currently having issues redrawing the decrypted image data, which is a pixel array in the form R,G,B,A. I thought this would be possible by simply putting the data into

ctx.putImageData(imgd,0,0);

But firebug tells me that the value does not implement the interface for imagedata. I have posted the entire array here. The image is 160px wide and 120px high.

Is there any way to reformat the array so that it is drawable on the canvas?

Answer

Trevor picture Trevor · Apr 1, 2014

Using Uint8 you can this much quicker:

var canvas = document.createElement("canvas"),
    ctx = canvas.getContext("2d"),
    img = [27,32,26,28, ... ];

// Get a pointer to the current location in the image.
var palette = ctx.getImageData(0,0,160,120); //x,y,w,h
// Wrap your array as a Uint8ClampedArray
palette.data.set(new Uint8ClampedArray(img)); // assuming values 0..255, RGBA, pre-mult.
// Repost the data.
ctx.putImageData(palette,0,0);

No need to go byte-by-byte unless you need to modify the values first.

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