Image scaling issues

Question

I am using a 1280x720 PNG for the background in my Flash movie, but when I play it in fullscreen the image looks like crap. What's the best way to make images still look good when the movie is scaled up? Should I use a 1920x1080 PNG and scale it down instead?

Answer 1

Let me help you understand.
Resampling occurs even without scaling on any bitmaps with smoothing enabled. A pixel level detail loss is noticable immediately, pixels are resampled until blurred.
Without turning on smoothing, the original image has no original resampling applied. Scaling performs a cleaner nearest neighbor resample that preserves hard pixels. At original size and while upscaling this produces a much cleaner result. While pixel edges are less resampled (upscale blur) the detail is still intact.
While turning smoothing on, the original image is immediately resampled (bilinear, trilinear, bicubic, etc). The pixel detail loss is immediately obvious even at original scale. This blurring helps during rotation and reduction but during upscale the amount of resampling get heavier and heavier until the image is excessively blurred. The only slight benefit is edges appear smoother, but the reality is the edges are blurred to death. This is why it very limitedly helps to some people but really doesn't help at all.
Here's an example of a small choice piece of a free Harley poster showing the effects of smoothing at original and 200% scales. An additional small portion of the original image is scaled 3x (nearest neighbor resampling (no smoothing)) to illustrate the difference in pixels even at original scale. The detail loss, while much less at original size, is still visible with smoothing.
Example Image
The top 3 images are with smoothing enabled. It's immediately obvious the level of blur is pretty harsh on the original image. The zoom-in shows the pixel blurring compared to the image with no smoothing below it. Color is shifted and muddied from bright to dark very noticably.
The upscaled image is where the real destruction takes place. The curved tire, angled spokes and spring are the most harsh environment for nearest neighbor scale. Smoothing has blurred them so much in the resample they appear a lot smoother. Only it's so blurry you can barely look at the picture without your eyes watering. To a photographer, this is a throw-away photo, far too out of focus.
The bottom image shows no smoothing enabled. The original size bitmap retains a great deal more pixel clarity and detail. The 300% zoomed image shows much brighter, more accurate colors having not been resampled. During the upscale the pixels are only nearest neighbor therefore you can see the extremely slight anti-aliasing performed. Hard pixels stand out more, much more true to the original image. Highlights on metals are still bright, colors are more accurate and more pixel level detail is exposed and enlarged. While edge enhancement would be nice, it looks far better without blurring the details and colors out of existence.
Therefore smoothing really doesn't help upscale or even original size without pixel and color destruction. The best option is not to require Flash to perform any scaling on a bitmap unless edge-only resampling becomes available. The small benefit it gives is working with a far less quality bitmap which might render some slight performance advantages in memory ops for huge images. At the loss of detail, this is arguably more of disadvantage than advantage.