In a previous post, I demonstrated how to use
RenderOptions.BitmapScalingMode in WPF to change the quality of
the resize of an image. Some folks have questioned why that is
necessary when the resizing worked just fine in 3.5sp1
In .NET 4, the default BitmapScalingMode changed from Fant to bilinear for performance
reasons. The Fant scaler is CPU-intensive whereas the now default
Bilinear is handled by hardware.
The net result is a move from 3.5sp1 to .NET 4 will show, in
many cases, decreased quality but increased performance for resized
bitmaps. The actual result depends on how much resizing you are
doing (resizing to less than 30-50% of size will generally show
artifacts).
To reset to Fant, you can set the RenderOptions.BitmapScaling
mode in the root of each window. The image below shows a comparison
between the two scaling modes for two fairly large images. The
first scaling is down to 400px widthfrom 3008x2000 fro the police
line image and 3374x2257 for the roses image: both are pretty
significant resize options.
(view full size to see the comparison)
These close-ups show how bilinear really starts to break down at
small sizes. The 50x50 image can still be understood in fant, but
in bilinear - not so much.
Another option, of course, is to use images that are closer to
the resolution you require. When you resize to something closer to
the source resolution, the hardware resize does a passable job.
Keep in mind that this will also affect ASP.NET
applications that use WPF server-side for
image resizing (an increasingly common practice)
