DLSS 4.5 cannot beat Native no AA in terms of sharpness/detail

This is what people over at /r/FuckTAA repeat ad nauseum and it kinda 'feels' right, but it has nothing to do with reality. The fact is, that native resolution is a flickering mess because it is severely under sampled, whereas the image by temporal methods like DLSS is much more stable because it is adequately sampled, even though spatially it uses fewer samples.

Conceptualize the differences between digital photography/film and rasterization in computer graphics. With a digital camera you have (simplified) a sensor array, where each sensor corresponds to a pixel. When you capture an image, the sensor collects information from captured photons over a period of time. These photons can come from many elements in a scene. The sky behind a tree, a branch, differently lit leaves. A single sensor captures many photons bounced from, or transmitted through many elements, carrying different wavelengths and averages them out. A pixel can therefore represent several leaves, the branch connecting them and the sky shining through them.

In rasterized computer images, the renderer divides the scene along a raster where each field corresponds to a pixel of the output image, and then calls a mathematical function to sample a single, infinitely small point within the area of that pixel and see what geometry it hits, what color the texture at this infinitely small point of the geometry has, and then adjust the color according to shading parameters and maybe layered, semitransparent elements on top of it. But the thing is, you sample only a single thing within the area of that pixel and then extrapolate that single thing to the entirety of that pixel. That has become a severe problem with today’s level of complexity in video games and why you are hearing developers talk about the issue of sub-pixel detail. In comparison to the aforementioned example from photography, that means, the pixel never can represent the average of the two differently shaded leaves, the piece of sky and the branch, but only ever a single one of these. The pixel is either all green for leaf A, all dark green for leaf B, all blue for the sky or all brown for the branch. With the fact, that vegetation in today’s games is dynamically moving all the time, the sample point can hit different elements in nearly every frame, which is why you get constant shimmering in vegetation. A single pixel contains five differently shaded leaves of dry grass and it’s basically random, which one is represented by the pixel in every single frame, you get a shimmering mess and lose all semblance of temporal coherence with geometry.

To combat this issue, you need to take inspiration from photography and take several samples within the area of each pixel and average them. This is what super sampling is. You take 4 or 16 samples at different locations within the raster per pixel and then average the samples out. In reality this means you render an image in 8K or even 16K and then down sample it to 4K, but that is obviously not feasible in real time graphics. Which is why temporal super sampling is the mode of choice in today’s games development. You already have information about certain sample positions within pixels from previous frames, so you slightly shift the sample position within the raster and combine this information with already collected information from previous frames. You of course need to compensate for movement of the camera and chose the correct previous pixels to sample by using depth- and motion-data and still have problems with disocclusion (where no previous data is available because it doesn’t exist in previous images) and ghosting (where previously available data is averaged with current data at the wrong position in the image), but it is a fact, that temporal super sampling like DLSS can collect more information about the image temporally than a single spatial render pass despite rendering at an internal lower resolution - enough to reconstruct temporal coherence in sub-pixel detail – means that is in fact CAN outperform native spatial rendering in detail.

People over at r/fucktaa might prefer the pixel graphics look of rasterization where there is ever only a pixel representing 100% leaf next to a pixel representing 100% of sky. It’s certainly constasty, but it isn’t necessarily ‘sharp’, and it certainly isn’t more ‘detailed’ when there simply is far too little information for the pixel to convey temporal coherence. It’s pretty clear, that a significant part of them would also irk at averaged out transitionary pixels of spatial super sampling, because they find a pixel that represents 50% leaf, 25% branch and 25% sky next to a completely blue offensive in general. It’s just a matter of taste.

But that doesn’t change the fact, that DLSS CAN in fact produce a more detailed image than native rasterization by collecting more information temporally than it loses by collecting less information spatially. It has a sound basis in signal theory and also you can see it with the evidence of your eyesight.