Generate proper header and append pixel colors - and you have a valid BMP image just for free!

pixelsToImage.js

var bytes = [
	0xff0000, 0x00ff00, 0x0000ff,
	0x0000cc, 0xcc0000, 0x00cc00,
	0x00ee00, 0x0000ee, 0xee0000,
];
var img = pixelsToImage(bytes);
console.log(img.src);

img.width = 90;
img.height = 90;
img.style.imageRendering = 'pixelated';
document.body.appendChild(img);

////
//// Functions:
////

function genBmpHeader(w, h, bpp, pad, size) {
	pad = pad || 0;
	var buffer = new ArrayBuffer(14
		+ 40 // + 4 + 4 + 4 + 2 + 2 + 4 + 4 + 4 + 4 + 4 + 4
	);
	var view = new DataView(buffer);
	
	// BM
	view.setInt8(0x00, 0x42, true);
	view.setInt8(0x01, 0x4d, true);
	
	// File size
	view.setInt32(0x02, buffer.byteLength + pad + size, true);
	
	// Pixel data offset
	view.setInt32(0x0a, buffer.byteLength + pad, true);
	
	// 0E	14	4	the size of this header, in bytes (40)
	view.setInt32(0x0e, 40, true);
	
	// 12	18	4	the bitmap width in pixels (signed integer)
	// 16	22	4	the bitmap height in pixels (signed integer)
	view.setInt32(0x12, w, true);
	view.setInt32(0x16, h, true);
	
	// 1A	26	2	the number of color planes (must be 1)
	view.setInt16(0x1a, 1, true);
	
	// 1C	28	2	the number of bits per pixel, which is the color depth of the image. Typical values are 1, 4, 8, 16, 24 and 32.
	view.setInt16(0x1c, bpp, true);
	
	// 1E	30	4	the compression method being used. See the next table for a list of possible values
	view.setInt32(0x1e, 0, true);
	
	// 22	34	4	the image size. This is the size of the raw bitmap data; a dummy 0 can be given for BI_RGB bitmaps.
	view.setInt32(0x22, size, true);
	
	// 26	38	4	the horizontal resolution of the image. (pixel per metre, signed integer)
	// 2A	42	4	the vertical resolution of the image. (pixel per metre, signed integer)
	view.setInt32(0x26, 2835, true);
	view.setInt32(0x2a, 2835, true);
	
	// 2E	46	4	the number of colors in the color palette, or 0 to default to 2n
	// 32	50	4	the number of important colors used, or 0 when every color is important; generally ignored
	view.setInt32(0x2e, 0, true);
	view.setInt32(0x32, 0, true);
	
	return String.fromCharCode.apply(null, new Uint8Array(buffer));
}

function pixelsToImage(ints) {
	let W = Math.sqrt(ints.length) | 0;
	let pixelData = ints.map((b, i) => {
		let bp = String.fromCharCode((b>>0)&0xff, (b>>8)&0xff, (b>>16)&0xff, (b>>24)&0xff);
		return bp;
	}).join('');
	let header = '';
	let img = new Image();
	
	let pad = new Array(0).fill('_');
	
	img.src = 'data:image/bmp;base64,' + btoa(genBmpHeader(W, -W, 32, pad.length, pixelData.length) + pad) + btoa(pixelData);
	return img;
}