On Thu, 2010-02-04 at 23:34 -0500, Devin Heitmueller wrote: > Hey Andy, > > The visible effects of the anti-alais filter could possibly be: > > > > 1. Less range of color, if high freqs of the color get attenuated. > > (Most people likely will not perceive this as most people are not that > > sensitive to small color variations.) > > > > 2. Loss of rapid variations in Luma - softer edges between light and > > dark areas on a scan line - if higher freqs of the Luma get attenuated. > > > > but given that the anti-alais filter is essentially flat out to about > > 5.6 MHz and has a slow rolloff (only 3 dB down at about 6.9 MHz), I > > doubt anyone would ever notice it is on with NTSC. Hi Devin, I think I miscommunicated in the above. To be more precise, I should have said: "The visible effects of the anti-alias filter, on a signal that does not have unexpected high frequency components out of the normal channel bandwidth, could possibly be:" In other words "here's what someone might notice as degredation due to an AA filter, if they had a proper signal throughout the entire amplifier chain." > To give you a better idea of what I'm talking about, look at this image: > > http://imagebin.org/83458 OK. It look pretty regular which is surprising, but nice for analysis. It's approximate frequency after having been being folded down is about: 42 cycles/line / 704 pixels/line * 13.5 Mpixels/sec ~= 805.4 kHz ~= 1 MHz which means it's likely a pretty high frequency, several MHz above the Nyquist rate, before being folded down by the sampling. > The above image was taken with the generator via the s-video input > (ruling out the possibility that it's any sort of product of > intermodulation). You are correct that intermodulation product is the wrong term in the case of basedband S-Video. However, clipping caused by an overdriven amplifier will introduce high frequency components - be the peak of the time domain signal caused by mixing of unwanted TV stations or just a very strong or overamplified basedband signal. > For the sake of comparison, here's the exact same signal source > against an a similar em28xx design but with the tvp5150. > > http://imagebin.org/83459 Much nicer. > > Since you have a signal generator, you should run experiments with PAL-D > > and SECAM-D with a grid containing vertical lines since those both have > > a 6.0 MHz video bandwidth. SECAM also has FM color, so you might see > > the greatest affect of an antialias filter on color on the Cyan color > > bar in SECAM-D. > > Believe it or not, I'm actually having trouble with the generator > right now with anything but NTSC. I'm going back and forth with > Promax on repair options. So I cannot do any PAL or SECAM testing > right now. :( I'll try to perform a quick test with my PVR-350 with NTSC and the YUV capture device BTW. Then I'll go outside and shovel more snow. :P Regards, Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
