Most browsers do not make it easy to draw perfect 1-pixel-wide lines; usually they are two pixels wide and weaker than the color you want. This little hack fixes that and some image smoothing problems.

canvasnosmoothing.js

function pixelPerfect(ctx) {
	ctx.translate(0.5, 0.5); // so pixels with odd coordinates snap to nearest physical pixel
	ctx.imageSmoothingEnabled = false; // may need polyfill for safari
}

// Call pixelPerfect with your canvas context (obtained by getContext) as argument, and happy whole-pixel drawing!