Which video signal to use?

[timtheenchanteruk]

Hi, I will next week be using a projector with a DVD player for a production.

 

We will be projecting onto a set of white tabs (the folds in the tabs giving a desired effect of ripples) But I am unsure as to which signal to use for the best quality, both the DVD player and the Projector have S-Video, Composite, And video outputs/Inputs.

 

Any suggestions on which gives the best image, or will the difference be outweighed by the type of material I will be projecting onto?

[danburns]

You don't say what the plain video output is. Is this another composite?

 

S-Video usually gives better quality because it carry's certain components separately. There was somewhere a table that compares all the different types of connections but I currently can't find it.

 

Although you may not see much difference, depending on the quality of the video/surface being projected onto/length of signal cable.

 

d

[Bobbsy]

Between S-Video and Composite, S-Video should be considerably better, with improved resolution and much less cross-colour interference. However, I've not quite clear what you mean by "video" as opposed to composite.

 

Bob

[dbuckley]

Everything you ever wanted to know: http://www.kat5.tv/videoformats.html

[timtheenchanteruk]

the composite, as labeled projector are 3 seperate phono connectors labeled Y (coloured green) Cb/Pb (coloured Blue) and CrPr (coloured red), with composite written across the top af all three,

and a standard yellow phone for the video (as in the normal scart type of video).

 

The length of the cable is short (around 2-3m)

 

Ah, upon reading the link, it seems the projector is actually meaning Component Video rather than composite, as its written

[Andrew C]

Short throw, short cable, onto tabs, (coloured?) it matters not a jot which connections you use.

[timtheenchanteruk]

Thats what I thought, they are white tabs, but tabs is tabs when said and done, the projection distance is around 10`, so yes short as well

[Pete McCrea]

I'd echo Andrew C's comments that it really won't matter that much. I'd do it in composite or SVideo. Probably composite as it's one esy to coil cable. SVideo cables are a PIA to coil..... We either tend to go composite or Data. In the 1 and 1/2 years of Production:av I've only done one gig in Component.

 

The Kat5tv link is worth a read, as it explains the signals well, and worht adding to the wiki.

[SeanT]

I use a component connection if I can anticipate using it beforehand and add it on because I'm picky, or into a scaler from a DVD player coz I like it. I use RGBs for DVD and Sky at home, followed by DVI after deinterlacing and scaling, coz I can B-) (it's true that at work quality is less of an issue)

[David Lee]

the composite, as labeled projector are 3 seperate phono connectors labeled Y (coloured green) Cb/Pb (coloured Blue) and CrPr (coloured red), with composite written across the top af all three

 

Err thats component - if your dvd outpuits RGB (poss via scart adaptor) you could use that for quality.

 

Note - scarts are rubbish domestic connectors that are liable to fall off if you move the thing. If your lucky, the DVD will have the RCA outs for component.

[paulears]

yuv isn't the same as rgb. If you have a source vt like the old BVU range, or beta sp, then the component output is via terminals labelled as you stated - the 4 pin s-video connector that sprung up with the introduction of S-VHS simply separates chroma and luminance info. quality wise, then rgb is normally the least trouble and best quality - but you don't get it as an output on a ot of kit. Scarts have been bodge designed to cater for ins and outs in umpteen variations, often auto switched. So just because you have a full 21 pin wired scart cable, doesn't mean you can use RGB. the yuv style of component.

 

The U and V elements provide color information and are "colour difference" signals made up of the blue component minus luma (B-Y) and the red component minus the luma element (R-Y). By doing this matrixing at the camera end of the chain, you get composite analogue signals (YUV). The benefit of doing it like this is simply bandwidth. The luminence channel (B&W brightness) is twice the bandwidth of the colour info, so one full range channel plus two smaller ones make better use of bandwidth. For what it's worth we talk YPbPr for analogue and YCbCr for digital signals.

 

Upshot of all this is that any form of combining these separate signals into one cable introduces artifacts that we don't want because image quality is compromised. So my order of quality (note-mine) is:

RGB

YUV

Y/C

Composite

RF

 

What needs to be considered, after saying all this is that other factors do apply.

 

Just because a device has component signals available does not mean they are good quality. equally, if you have a domestic widescreen TV like mine, just because it has y/c inputs does not mean (Mr Panasonic) that they give better pictures. On mine, using a really good camera with a nice lense, switching from comp to y/c produces a difference in picture quality. On y/c, colour detail seems to improve, or is it just my eyes when the colour seems to ramp up a bit. On a test chart, there is a small change to apparent horizontal resolution, but I suspect this is the removal of some of the chroma artefacts that 'colour up' the lines on the chart, rather than an increase in resolution I can measure.

 

Y/C is also a really easy connector to break, get the orientaton wrong and you bend the tiny pins - a single BNC is much more reliable. Phonos, in any shape or form I hate, horrible flimsy things. The sockets are frequently soldered direct to the circuit board and giving the cable a tig can break the pins off!

 

The real secret is simply getting the best quality signal you have to its destination, using the highest one up the quality list you can. If you have a really good monitor or projector, it is worth it, but if not - the extra difficulty and expense of clever connections may simply not be visible. You have to try it and see!

[Tomo]

In summary:

For analogue video signals, choose the connection with the most pins!

 

(Although D-sub VGA cable isn't good for runs longer than ~20m)

[Ben...]

Upshot of all this is that any form of combining these separate signals into one cable introduces artifacts that we don't want because image quality is compromised.

 

...unless you use serial digital video :o

(a.k.a. SDI, to be found on pro TV kit)