Disabling antialiasing on a WPF image [closed]

Question

I'm writing a small Login dialog, and have embedded a banner at the top of the dialog for aesthetic reasons. All went well, except that by default, WPF anti aliases the entire image, making the text that was contained within it frustrating blurry.

After a bit of searching, the first few pages of results showed that it's common belief that anti aliasing cannot be disable in WPF. Can any confirm, or otherwise deny this?

It's a minor issue for me - I'll take the text out of the image and instead superimpose a label with the same text on top of the background image to achieve the same effect (though I must admit, it's a bit annoying).

Thanks, Rob

Impatience

Another (automatic) way for avoiding sub-pixeling: https://mcmap.net/q/905322/-drawingcontext-drawline-pen-has-no-full-opacity – Zoom

Note that the exact same problem can occur if the Windows DPI settings have been modified (to use e.g. 125% or 150% font size). This will also result in bitmaps being upscaled, making things look "funny" (or rather, ugly...). We could add a separate question about that, since the answer/solution is very much the same. – Spinal

Answer 1

As far as I know, WPF always does anti-aliasing when scaling a bitmap. However you should be able to accomplish your goal by avoiding the bitmap scaling.

There are two steps:

1. Set SnapsToDevicePixels="true" on your image
2. Set a ScaleTransform on your image to scale it so that one device pixel = one bitmap pixel

To compute the needed ScaleTransform, compute your screen's DPI like this:

var DPI = Win32Functions.GetSystemMetrics(SM_CYICON) / SystemParameters.IconHeight * 96;

and then for the bitmap, do:

var scale = bitmapDPI / DPI;
var transform = new ScaleTransform(scale, scale);

This will cause your bitmap's pixels to exactly match with the device pixels. WPF will not stretch the bitmap, so there should be no anti-aliasing.

If you do want to stretch your image on high DPI screens but do so without anti-aliasing (eg double all pixels), just stretch the bitmap in your own code using whichever algorithm you like and use the above with the stretched bitmap.

Twin

Thanks Ray - this comment helped me A LOT today actually! I was using an InteropBitmap as the Source of an Image and it was always being scaled to look really ugly (even though the bitmap DPI was 96, which is different to the display DPI). Adding a ScaleTransform to "scale it down" helped, it now looks like it should. Bounty coming up, but because of SO limits I have to wait 23 hours before giving it to you. :) – Spinal

Bounty given as promised. :) I improved your answer a little also at the same time. – Spinal

Answer 2

It's not really anti-aliasing - it's sub pixel positioning that causing the problem, I've written about it (and about a control that solves the problem) on my blog at:

http://www.nbdtech.com/blog/archive/2008/11/20/blurred-images-in-wpf.aspx

Jaunitajaunt