Pre-Scaling before Bilinear Scaling?

[rsn8887]

Is it possible to give winUAE the option of integer pre-scaling before further bilinear filtered automatic scaling, such as found in MAME? Or does it already do that and I am just to dumb to find the option?

This would give a control over the "blurriness" of the scaled pixels while getting rid of the horrible pixel wobbling that plagues point filtered non-powers of two scaling.

For example, if scaling to fullscreen, the total scaling might be non-integer. If it is larger than 2*, the bilinear filter will be quite blurry. With an (unfiltered) prescale of 2*, the bilinear filter will only be applied on the small extra scaling needed to reach the desired value, and the blurriness is reduced by a corresponding factor. This works wonders in MAME, and goes especially well with hi-res screenmodes and lo-res sources, e.g. for amiga lo-res resolution on a hi-res host it would be awesome!

[ajk]

That is essentially what I have done when uploading Amiga stuff to YouTube, ie. double/triple/quadruple the pixels up as many times as fits first, then do the final scaling with bicubic or other soft interpolation, it works well.

[bladecgn]

Originally Posted by ajk

That is essentially what I have done when uploading Amiga stuff to YouTube, ie. double/triple/quadruple the pixels up as many times as fits first, then do the final scaling with bicubic or other soft interpolation, it works well.

Prescaling would really be a nice feature. It works very well in MAME on my TV set.

[Toni Wilen]

Horizontally you can select superhires (Display panel) to get 4x pixels (if lores) or 2x pixels (if hires). Vertically there is only doubling.

[bladecgn]

Yes, this does have a positive effect (=sharper) if the Amiga display mode is low or hires for example.

It has no noticeable effect if the Amiga display mode is highres no flicker. Probably because this is already super-hires?

So I am really wondering if a (selectable) prescaling (e.g. 4 or 8 or even more times) followed by a reduction to the actual host display size would further enhance the picture.

[rsn8887]

Just to make the point for prescale stronger (I understand it might not be feasible to implement in WinUAE, but it would be so great ):

I just tested the latest WinUAE on my new retina display, and it is quite blurry with bilinear in any mode, or there is pixel wobble if I turn bilinear filtering off.

I think a 2*, 4*, 8* prescale option becomes more and more important the higher your host resolution gets. The bilinear filters will create more and more blurring the larger your host resolution. As we move to retina and/or 4k displays this will become more of an issue.

It is very important to have a prescale option in both horizontal and vertical directions, otherwise I get an anisotropic blur only in the vertical direction. This can be quite distracting.

Mame is a great example for the benefit of prescale. This was one of the main reasons back in the day why I bought into the new Mame philosophy of using a single resolution with prescale and bilinear for ALL games. Before that, I almost killed myself trying to match my CRT resolution to the resolution of each game as well as possible to get 1:1 pixel mapping, using the stretching on my crt etc. This is not possible anymore with LCD screens, and, if we have pre-scaling, we can still have a great, sharp image, without pixel wobble.

[mark_k]

Here are some real-world example pics. I took these on an Android phone (1280×720 screen) when running the Snes9x EX Super NES emulator. The emulator scales the 224-line game image to 720 output lines, i.e. by a factor of 45/14.

There are three screenshots. One with no linear filtering, one with linear filtering (224→720 lines), and one with 2× prescaling and linear filtering (448→720 lines). The image with prescaling is significantly less blurry. You might want to download then view at 100% scale in a paint package in case your web browser scales the images.