Component and S-video outputs - do they have an "effective" resolution?

[Graham Hickling]

I've been pricing out cheapish DLP data projectors for academic presentations. I'd like one that also throws a good picture when connected to my HC1 and/or Linkplayer.

All the projectors are greater than SD resolution (i.e. 600x800 or 1024x768). All of them accept 'S-Video" Y/C input, and some also accept component. The camera and Linkplayer can output either.

What I'm wondering about is the "effective resolution" of the Y/C versus component signals. On a 600x800 projector, will 720p component output look sharper than S-video output? What about on an a 1024x768 display?

Basically, I'm confused about how to compare apples and oranges...

[Matt Davis]

Originally Posted by Graham Hickling

I've been pricing out cheapish DLP data projectors for academic presentations. I'd like one that also throws a good picture when connected to my HC1 and/or Linkplayer.

Getting quality out of a projector means feeding it with carefully refined signals. Don't let a cheap projector 'work hard'. If it does 800x600, feed it 800x600.

Let's say we have a YC input for video and an XVGA input for your laptop. The video gets scaled up to fit the native rez of the projector. If you buy a 1024x768 device, then obviously the sharpest results are going to come from that rez, not 720x576 (and the pixels aren't even square). Here's where a spot of cunning and the use of HDV can help.

If you were to shoot, capture and edit at HDV (Sony or JVC flavour), then output to 1024x576 progressive and compress to WM9 (PC) or PhotoJPEG 75% (Mac) you will get great looking video that will import into PowerPoint (PC) or Keynote (Mac) and be as sharp as the slides (not the fuzzy mush you can get with some projectors). The process is convoluted and non-intuitive to start, but it gets easier.

Please note that there is a delay whilst the projector takes in video and scales it for final display (4-7 frames - so feed the audio to the projector too or your video sound will be out of sync). Also, video is interlaced, projectors are not; therefore the projector will deinterlace video and maybe even throw away half the resolution (and futher delay sound by 1-2 frames). The cheaper the projector, the worse video can get. And if the sound's out of sync, you're toast even though it's Not Your Fault (tm).

I've got WM9 videos (sorry, can't share due to the content) that play in PPT and look better than a DigiBeta composite feed on the same projector simply because my video didn't have to jump through as many hoops of fire as the digibeta (no, but the person creating the file did).

The sweet spot (IMHO) is a DLP that has a 1280x1024 native rez, a video that started out as HDV and has been deinterlaced if necessary and quietly scaled to 1280x720 and compressed to WM9 at 5mbps on a 3GHz PC. Pop that puppy into PowerPoint, back up a little and enjoy.

[Devlyn Hukowich]

In the old days of analogue video this question would have cause a holy war with broadcasters on the component side and prosumers on the other.
You are always better off with component that Y/C or composite. The question is if the component output is 720P or just SD. Y/C or composite is always NTSC (59.97fps/525lines), component can be anything.
As far as effective resolution goes, Y/C is around 400 horizontal lines (always 525 vertical lines) this depends on the source, the length and quality of the cable. A cheap 6 foot Y/C cable will give the maximum resoultion, but longer distances will limit resoultion and possibly cause colour alignment problems. Component cables have their issues also. They all have to be exactly the same length and variation between the lengths will show up as a colour phase (hue) shift. This is why broadcast equipment has proc amp controls on everything. Again component resolution can be limited by cable length and quality.
Let me get down off the soapbox.
Stick with component where possible. Y/C when component is not possible, but keep the cable lengths short & for long runs stick with a high quality cable and composite.

Hope this helps.

[Graham Hickling]

Thanks for the detailed answers, guys!

Devlyn - both the Linkplayer and the HC1 can output true 1080i (the Linkplayer can output 720p as well.)

If S-video with decent cabling outputs "525 x 400" lines, does that imply it might not look any sharper through a 1024x768 than through a 800x600 projector? Is a "line" even vaguely equivalent to a "pixel"?

Matt - thanks, that was all good information (esp. the bit about audio delay which I'd never thought about). My main question though was about projecting the analog signal coming out of a videocamera or disk-player's video ports .... rather than from a computer's VGA port.

[Devlyn Hukowich]

Glad to help.

Every manufacturer uses different chips to accomplish the scaling (conversion from one resolution to another). This means that projectors will look different depending on which chip they use. Usually the problem is with down scaling, high resolution input to low resolution display (1280x1024 to 800x600). If the scaling is a harmonic or multiple then things tend to look better. Up scaling from NTSC (400 x 480*) to 800x600 or 1024x768 should be OK as the multiples are not really weird. 400 to 800 is 1:2 and 480 to 600 is 1:1.25. From what I have seen NTSC video generally looks good on projectors.

*Although NTSC is 525 lines only about 480 are visible as picture and on a TV only about 384 can actually be seen. Projectors tend to allow more visible picture than a TV can.

[R Geoff Baker]

Some cautions when discussing resolution:

Video resolution is expressed 'within a square' -- so when SD resolution via Y/C is described as '400 lines' this does not mean the image is 400 pixels 'wide' -- rather it means that 400 vertical lines would be resolved in an area of the picture width equal to the picture height. If the resolution was measured across the full width of the 4:3 image, it would be described as 530 lines ... but that isn't the standard, and that is not how it is described.

On the other hand, computer resolutions are described across the entire image -- 800x600 is a 'resolution' that would be translated to 600x600 if the conventions of video were used ...

None of this addresses what each format is capable of, or what it delivers -- it merely attempts to keep the language 'common' so that different paradigms can be compared. In the consumer realm, it has long been the standard to describe the theoretical maximum of a given format as the de facto resolution -- hence the standard claim that an SD digital signal (always 720x480 in NTSC world) resolves 540 vertical lines ... possible, but hardly typical. Note too that formats are _designed_ with limitations in mind -- SD digital video was designed to match the horizontal resolution (the only 'variable' one) with the fixed vertical resolution ... there is no perceived advantage to offering a better resolution on one axis than the other.

GB

[Wayne Morellini]

Originally Posted by Devlyn Hukowich

In the old days of analogue video this question would have cause a holy war with broadcasters on the component side and prosumers on the other.
You are always better off with component that Y/C or composite. The question is if the component output is 720P or just SD. Y/C or composite is always NTSC (59.97fps/525lines), component can be anything.
As far as effective resolution goes, Y/C is around 400 horizontal lines (always 525 vertical lines) this depends on the source, the length and quality of the cable. A cheap 6 foot Y/C cable will give the maximum resolution, but longer distances will limit resolution and possibly cause colour alignment problems. Component cables have their issues also. They all have to be exactly the same length and variation between the lengths will show up as a colour phase (hue) shift. This is why broadcast equipment has proc amp controls on everything. Again component resolution can be limited by cable length and quality.
Let me get down off the soapbox.
Stick with component where possible. Y/C when component is not possible, but keep the cable lengths short & for long runs stick with a high quality cable and composite.

Hope this helps.

Devlyn,

Does any of the following present problems on some projector inputs, or output devices:

I've read that comb filters etc might limit your resolution (from NTSC Servicing training manual and other information. My TV seems to limit the Svideo and component to composite resolution (Svideo and composite share luminance channels, and composite interference can even be seen in the composite channel) . So I get 320 or 360 pixels across (I am trying some new equipment shortly to see if it is the set top box and DVD limitations).

Now Svideo is supposed to get around 360-400 lines+ but the equipment might reduce this. Back to output device. I found references, I think in older Radeon 9000 graphics card output to resolution limitations being in place, but one Pal standard mode has the highest, probably over 350, maybe 450 lines.


Thanks

Wayne.

[Devlyn Hukowich]

Wayne,

There are any number of filters, picture enhancements and settings on a video display that could limit resoultion. Comb, Y/C, 3D filters, edge enhancement, picture, sharpness, softness settings, etc...
The filters typically only are used on the composite and Y/C inputs as conversion to NTSC causes problems with dot crawl and other colour issues. Some output devices are better than others. The term "your mileage may vary" applies here.

SVideo (Y/C) should push you to about 400 horziontal lines, but you are right equipment varies this. Now sending a PAL signal changes many things as PAL does not suffer from the some of the limitations that NTSC does. Hue shift & dot crawl being the big ones. My Radeon 9700AIW card says it can push a 800X600 image out of the composite/Y/C ports, but of course this can only really be NTSC at about 400 X 450. However some cards can display fine detail really well due to sharpening, etc...
I haven't found one yet but a resolution chart specifically for computer output might exist and be useful for testing this. If anyone has one let he group know. It would have to be for the resoultion you intend to display. My other thought is to use a DVD with the THX Optimiser on it. Some of the tests it includes are pretty good and don't require any additional equipment (a blue filter is nice though).

Regards,

Devlyn

[David Kennett]

To hopefully clarify matters.

Composite and S-video cables and connections are standard definition ONLY. If you run HD through them, you have reduced your HD to SD. Your HD resolution is GONE.

Comb filters are used only on composite SD signals to better separate the chroma from the monochrome. They have no purpose on component signals, whether digital or analog.

There are several projectors with native 1280:720 resolution, optimized for 720p video. They work fine with a computer too.

[Wayne Morellini]

Originally Posted by Devlyn Hukowich

Wayne,
Some output devices are better than others. The term "your mileage may vary" applies here.

Svideo (Y/C) should push you to about 400 horizontal lines, but you are right equipment varies this. Now sending a PAL signal changes many things as PAL does not suffer from the some of the limitations that NTSC does. Hue shift & dot crawl being the big ones.

My old Radeon gave a lot of Dot craw through PAL composite, it had a special mode that reduced it though (but probably res as well) or was that just using Svideo instead.

The problem with this TV/equipment is rather then having a true better, circuit in parallel to composite, I think they just use the composite as part of the Svideo/component circuit.

I haven't found one yet but a resolution chart specifically for computer output might exist and be useful for testing this.

I thought any res chart would do?

Graham,

You will loose your HD resolution, as standard, but might gain the SD resolution with better equipment. So, what David says is right, true HD is best.