| Showing a downsampled or highly recompressed alteration of a screenshot
would obviously completely miss the point. But even showing the raw
screenshots would be a compomise. Why?
Well, DVD frames consist of only 720x480 pixels for NTSC. People
often argue that showing these frames upscaled to any resolution
above that (1024x576, 1280x720 or 1920x1080) is a waste of time,
because "there isn't more information than 720x480 anyway"
or "you can't create detail from nothing".
While both statements are true, they COMPLETELY miss the point!
Upscaling 720x480 to a higher resolution is not about creating
'detail' that isn't there in the first place. Its about presenting
those 720x480 pixels on a display device with the least possible
amount of high frequency aliasing noise.
Huh? Ok, only because you have 720x480 SAMPLES of an analog medium
(like film in this case), doesn't mean that displaying them AS SQUARE
PIXELS WITH SHARP BOUNDARIES on a display device is the right form
of output to reapproximate the smooth analog waveforms it originally
captured! By upscaling digital samples to a higher resolution, you
interpolate a smooth waveform between the discrete samples. The
more interpolation steps the better. The ideal would be to use a
sinc filter that yields a sine wave, but thats currently too demanding
processing power wise. A typical interpolation that is used is bicubic
filtering, which is already better than bilinear filtering, but
not quite spline or sinc quality.
If you are a bit familiar with digital information processing in
the audio domain, you will see that this is exactly the same concept
that is used in DACs in CD players for years. Its called oversampling.
Think of the same thing in 2 dimensions and you are there.
So, again. Displaying 720x480 samples as square pixels means that
the difference between the square waveform and the ideal sine waveform
is noise that masks the actual detail in picture. This is what we
perceive as 'aliasing'. The harsh edge of the square yielding very
high noise in the frequency domain (fourier).
That is why watching a DVD on a high resolution device (e.g. 9"
CRT) at a high resolution like 1920x1080 does actually reveal MORE
detail (of that original 720x480) than a 800x600 digital device,
because actual detail is masked by less aliasing noise that distracts
Thats why i use the following strategy when doing screenshots analysis.
I scaled the 720x480 grabs to 1920x1080 also with a bicubic filter
to mimic what a Faroudja 3000/5000 or HTPC would do. To make my
own comparissons, i watch these images on my monitor (which is capable
of resolving 1920x1080) with a program that is able to switch between
2 images almost instantly (<1/30 sec, AcdSee).
To present the differences to others, like here on the web, i crop
out certain slices to highlight a certain issue (EE, noise, clipping,
As easy as that, no magic.