Secrets Q & A
- Written by Brian Florian and Colin Miller
- Published on 30 November 2007
- High Definition 1080p TV: Why You Should Be Concerned
- Page 2: Flat Panel HDTVs and the Caveat No One Wants to Talk About
- Page 3: Native 1080p Material - A Hidden Reality
- Page 4: But, Do You You Really Need 1080p?
- Part 5: Are 1080p Scaling Artifacts Worth Worrying About?
- Part 6: Conclusions About 1080p
- All Pages
Are 1080p Scaling Artifacts Worth Worrying About?
Is this a subtle difference not worth worrying about? Not really. Consider if we only had two lines, and they moved across the screen. They would vary in width, and vary in distance to each other, shimmering like an artificially sharp mirage.
In the next example, shown below, the 'original' image is the same, but the scaling method is more sophisticated, akin to what you could expect from better scaling algorithms. With the filtering/interpolating, as opposed to just doubling, the location errors are reduced (lines remain more or less evenly spread), though it's interesting to note that if you look at each line, it's different, in terms of where the darkest part actually is, since it needs to clump the 'peak' of dark to the nearest pixel location, regardless of where it should be.
The filtering and interpolation greatly reduces the obviousness of location errors, because it softens the edges of the line to do it, and averages the perceived center by weighting the degree of black in the smaller lines that contribute to the larger perceived line.
This is, certainly a better way to do it, but it must necessarily soften the edge, and as such, reduces the contrast of the detail as well. Instead of full black or white, we get variations in between, i.e., a lot of gray, and more relevantly, very little, if any, completely black or white.
Click on the photo below to see a larger, animated version. You may see a small square in the bottom right hand corner. If so, you need to click on that square to see the photo at full size.
While the 480p native pattern is crisp and maintains full contrast, the scaled up versions aren't. Now, we could say that much of the edges that are so crisp in the 480p native pattern aren't actual video data, but rather the pixel structure itself, and that is quite indeed true. However, what cannot be argued is that some degree of detail is in fact lost, in terms of contrast amplitude, AND that the characters of the lines will change, albeit more subtly, with horizontal movement.
This is most especially true with the 768p scaled image, where lines look visibly different, and even uneven, from line to line, illustrating that when scaling up, more resolution can be of pretty significant advantage in the preservation of fine detail, even with low resolution sources.
The pattern scaled up to the 1080p equivalent actually isn't too bad. Given what 1080p allows with a 1080p signal, we'll gladly take it.
It is interesting to note, though, that in both cases, higher resolution output image has less obvious artifacts, suggesting that if you were going to watch standard definition content on a high-definition display, it makes a case not only for the highest resolution display you can get, but also very good scaling algorithms that do the best job possible minimizing the visibility of these inherent scaling artifacts, while sacrificing as little detail as possible.
Don't get us wrong. Well-scaled standard definition content can look darn fantastic on a high definition display. We just wanted to point out that there's a compromise inherent to the 'upgrade.'
One of the easiest, Do It Yourself examples of scaling up poorly is simply feeding an LCD monitor, that's say 1280 x 1024, a computer desk top set to 800 x 600. The LCD has more than enough resolution, so to speak, but the text is fuzzy, icons are fuzzy, so everything's off. In fact, if the pixel phase and clock of the input signal are not set correctly, either by auto-calibration within the monitor, or manually in the setup menu, to map the pixel values from the scan line information, you can get similar effects even with the native input rate, in which some areas have clear text, but it gets fuzzy in others.
So, should we all just revert to native 480p displays? Hardly. The future is 1080p, and 480p is in the beginning of a gradual obsolescence. If you're going to pick an optimized display for a resolution, go for the new standard, which will be 1080.
Now, there's the argument that you can simply scale down the 1080p signal to standard definition, and if you can't see the pixel structure (i.e., if the screen is small or you are seated far away), it won't make any difference.
We say, "Bunk."
Below is the inverse of the above patterns, starting this time with 1920 x 1080, and then illustrating what happens when that gets scaled down to 1366 x 768 and 720 x 480 output respectively.
Click on the photo to see a larger, animated version. You may see a small square in the bottom right hand corner. If so, you need to click on that square to see the photo at full size.
Notice that when you scale down the fine detail, you get moiré patterns developing in the vertical lines. When scaled down to 1366 x 768, as the lines move across the screen, the new pixel locations fall in and out of phase with the original image values, and you alternate between sets of relatively clear line structures and gray areas. In other words, you create wider visual structures where the original image was merely fine texture. This is QUITE obvious, even if you can't see detail on the image at the level of a single pixel.
With the 720 x 480 output image, you get a similar deal, but without any fine detail, and with the same artifacts of wide areas of shading that, in the original image, simply don't exist. Now, you can take the argument that the 1920 x 1080 pattern is in such fine detail, that it doesn't apply to real world images. Oh, really? Has anyone ever considered that 1920 x 1080, the highest ATSC resolution HD format, is a mere 2 megapixels? Is somebody going to actually propose that the grille of a truck in the distance will neither move nor have closely spaced lines in the image? Hmmm?
Now, we will grant detractors of this example that many scaling algorithms will do a better job than performed in the example when it comes to trading off picture detail for lack of visible artifacts, but the fundamentals remain.
See why talking about 1080p is so important?