- From: Ian Hickson <ian@hixie.ch>
- Date: Tue, 14 Jun 2005 10:12:35 +0000 (UTC)
On Mon, 13 Jun 2005, Charles Iliya Krempeaux wrote: > Hello, > > I know people are going to want to read individual or groups of pixel > values. Certain image processing algorithms require it. (For > example, certain edge detection algorithms. Etc. There's alot of > different ones.) The problem is that it is quite easy for a single x,y coordinate of the canvas to have either multiple pixels, or have a pixel that is shared between multiple x,y coordinates. That is to say, <canvas> is resolution-independent. The units of the API calls are CSS pixels, which are a length, not an index into the bitmap that implements the canvas. When you say <canvas width="20" height="40"> ...the coorindate space for the drawing commands is a 20x40 space, but the actual bitmap depends on the actual size of the canvas when it is rendered. If CSS specifies that it is 100px x 50px, then the bitmap will (probably) be a 100x50 pixel bitmap. Except if you are on a printer or a high-res screen, in which case it might be more like a 600x300 dot bitmap. So which pixel do you return when you get asked for a specific pixel? -- Ian Hickson U+1047E )\._.,--....,'``. fL http://ln.hixie.ch/ U+263A /, _.. \ _\ ;`._ ,. Things that are impossible just take longer. `._.-(,_..'--(,_..'`-.;.'
Received on Tuesday, 14 June 2005 03:12:35 UTC