Why is GPU scaling so poor quality compared to display scalers?

[kasakka]

So how come using your GPU to scale the resolution to large results in a much, much blurrier image than using a display scaler?

Before I got a GTX770, most games on my Dell 3008WFP had to be played at 1080p on my 2560x1600 display and I noticed that using the display's built-in scaler resulted in images that were not really that bad. By comparison using the GPU for scaling was blurry crap.

You'd think that if anything, the GPU would be able to do much better processing for each frame to scale them right.

 

[LtGoonRush]

Interesting, usually the scaler on the videocard gives better quality images, though perhaps your monitor has an exceptionally good scaler. I'm using the nVidia scaler on my GTX 670 to downsample from 1600p to 1200p for better antialiasing and it's not blurrier than I would expect. It could also be that the scaler on your TV produces a sharper image with more stair-stepping or ringing artifacts, compared to the GPU scaler producing a less sharp but more accurate image. From some Googling I *think* the nVidia GPU scaler uses bicubic filtering, which is a relatively efficient algorithm that produces images that are accurate but not as sharp as possible. Older/cheaper monitors generally use bilinear filtering that is markedly worse.

Overall I would wonder if the scaler in your monitor looks better than the GPU for all content, or if there's some where it looks ugly and oversharp but looks right from the GPU scaler. Just a guess though.

 

[kasakka]

Overall I would wonder if the scaler in your monitor looks better than the GPU for all content, or if there's some where it looks ugly and oversharp but looks right from the GPU scaler. Just a guess though.

The display scaler gives universally better results, even for desktop. It does have a sharpness control that may add a little bit of sharpening but I don't see any ringing or other anomalies at its default setting.

 

[KingFatty]

Is it possible the GPU scaling approach is somehow producing output that is mismatched to the display, so then the display has to go and also apply its scaling to the already-GPU-scaled image, so you are getting double-scaling from both the GPU and display when you select GPU scaling, and so it looks way worse?

 

[Wall Street]

I wonder if the display may have dedicated scaling hardware vs. a software scaler in the GPU which could allow the display scaler to use a higher quality algorithm. That is just speculation on my part though.

 

[gorobei]

gpus typically you software scalers, if they dont have a license for some of the better algorythms the result can be underwhelming.

back in the dvd boom years, the best quality video came from dvd players using faroudja chips. http://en.wikipedia.org/wiki/Faroudja
looks like he sold the company and the technology was acquired by STME.

monitors and tvs use fixed function chip scalers, so the results can look much better than gpu software.

 

[KingFatty]

Maybe give us a listing of the various settings you used in the Nvidia control panel for the scaling, and also your monitor type and what settings you configured in the monitor's on-screen menu stuff, maybe something will jump out as being a possible thing to change or adjust?

 

[kasakka]

I've basically only changed the "perform scaling using" option to GPU and checked the box that disallows programs from changing the setting. If I turn the display's sharpen setting down from 50% (default) it gets noticeably blurry. Above 50% shows ringing so I'm guessing 50% is very minimal or no sharpening. Afaik in reviews the scaler has been noted as being particularly good.

Now considering I'm probably going to get a new display that doesn't have a scaler, I'm wondering if it's possible to add some sort of sharpening filter that would essentially solve the issue for GPU scaling.

 

[Anarchist420]

i use my monitor's scaler but only because GPU scaling/centering is less responsive/more laggy.

 

[f1sherman]

well I remember Timothy Lottes former Nvidia employee mentioning that writing a "proper scaler" is on his to-do list.

I haven't noticed any blur compared to Display scaling, only lag...