Pads an image with a specified amount of zeros on the top, left, bottom and right.

zeropad.js

function zeropad(image, top, bottom, left, right) {
    // Pads an image with a specified amount of zeros on the top, left, bottom and right. 

    // Validate inputs
    const image_size = image.height * image.width * image.depth;
    if (image.data.length != image_size) {
        console.log("Error: image dimensions do not match rgba buffer size!");
        return null;
    }
    if (image.data.constructor !== Uint8ClampedArray && image.data.constructor !== Float32Array) {
        console.log("Error: image data should be of type Uint8ClampedArray or Float32Array!");
        return null;
    }
    if(top < 0 || bottom < 0 || left < 0 || right < 0)
    {
        console.log("Error: the padding amounts (top,bottom,left and right) should be non-negative integers!");
        return null;
    }

    // Compute output dimensions
    const output_height = top + image.height + bottom;
    const output_width = left + image.width + right;
    const output_depth = image.depth;

    // Init output image        
    const output = {
        height: output_height,
        width: output_width,
        depth: output_depth,
        data: new image.data.constructor(output_height*output_width*output_depth) // Initialized with zeros
    }

    // Copy input image into output
    let output_idx = top*output.width*output.depth + left*output_depth; 
    let image_idx = 0;
    for(let y = 0; y < image.height; y++, image_idx += image.width*image.depth, output_idx += output.width*output.depth)
        output.data.set(image.data.slice(image_idx, image_idx+image.width*image.depth), output_idx)

    return output;
}

function zeropad768x768(image)
{
    // Compute padding amounts
    const output_height = 768;
    const output_width = 768;
    const top = Math.floor((output_height - image.height) / 2);
    const bottom = output_height - image.height - top;
    const left = Math.floor((output_width - image.width) / 2);
    const right = output_width - image.width - left;

    return zeropad(image, top, bottom, left, right);
}

// Utility function (only for testing)
function show_image(image)
{
    str = "";
    let idx = 0;
    for(let y = 0; y < image.height; y++)
    {
        for(let x = 0; x < image.width; x++)
        {
            str += "[ ";
            for(let z = 0; z < image.depth; z++)
                str += image.data[idx++] + " ";
            str += "] ";
        }
        str += "\n";
    }

    console.log(str);
}

// Test
test_image = {
    "height": 3,
    "width": 4,
    "depth": 4,
    "data": (new Float32Array(3*4*4)).fill(1)
}
show_image(test_image);
/* should output:
[ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] 
[ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] 
[ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] 
*/
output = zeropad(test_image, 1, 2, 3, 4);
show_image(output);
/* should output:
[ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] 
[ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] 
[ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] 
[ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 1 1 1 1 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] 
[ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] 
[ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] [ 0 0 0 0 ] 
*/