Independently controled key output

General
1

Hi all.
Is it possible to control ONLY key-output resp. alpha channel of some layer?
I have read about AMCP commands MIXER KEYER and MIXER CLIP, I try both thees commands, but always also the fill-output (RGBl) is affected. My goal is to achieve for instance black alpha (key-output) and full rendered unaffected template in the RGB channel.
J

2

I don’t see much use for this, but it’s possible by switching to straight alpha keying mode and use MIXER OPACITY to fade the image away. That gives you a black key out and a full YUV (SDI video is not RGB) out. But beside of being a very cumbersome preview out, this does not make sense at all. And it does only work with vision mixers, that supports straight alpha keys. So for instance all ATEM’s are out. There is a better way to get a cheap preview out. Use a screen consumer or see the Decklink Mini Monitor.

3

What you are describing is basically straight alpha.
Internally CasparCG composites everything as premultiplied alpha, so the colour information you want to see is not available at any point.
2.1 does support outputting straight alpha, but it won’t show anything more than premultiplied.

4

I just tried it with 2.0.7: It does not realy work, as it does the premultiply by tricking something with the grading of the colors. But anyway I don’t see any use for this beside a primitive way to fake a preview.

5

This is not a fake…:slight_smile: This is a pretty straightforward solution of the preview. We used it many years in our SD system for the onair graphics at broadcast from the sports matches. We have a graphics OB van with graphics station, which sends both fill and key signal to main OB van, where this signals are keyed to the output signal via vision mixer (Kahuna, Sony, Kayak). No need any additional cables monitors for preview signal.
Not to mention that for instance fade out looks better with the straight alpha, beacause premultiplied alpha makes a shadow effect.

Which workflow do You recommend for the clasic schema of taking lower third titles (Preview-AnimationIN-AnimationOUT) if I have to use separate channel for preview my HTML templates?
It will be possible to clear the output channel and add template to preview channel and then (after visually control the title) set IN animation to start, use SWAP AMCP command and start IN animation? Is it a good practice?
J

6

This WAS a solution back in the SD days, were a Targa or Matrox DigiMix card costed 7’000 to 10’000 bucks. And a second channel license for the CG software another 10’000 or so. I know. I saw these days also. Today you can have a two channel SDI fill and key card for 500 bucks and a simple preview out card for 150. So, no reason to not change workflows from time to time :slight_smile:

For Sony, Kayak and Kahuna you need to set Caspar to Straight alpha out. That works ok, I used it many times in OB vans with Sony and GV mixers. But, as the rendering is done premultiplied, this old trick does not work any more.

Just send a CG ADD command with autoplay enabled and the data fields to the preview channel and after review the same command to the program out. Alternatively you can send the program outs CG ADD without auto play and send a CG PLAY on cue.

By the way, SWAP is for layers and not for channels.

7

Yes I understand the logic of CG commands, but I am a new in Caspar and I have tryied to make and play only very simple HTML templates so far.
SWAP commands is for swaping layers BETWEEN channels, so I have expected, that will be better for performance to swap layers between preview and pgm channel instead of sending two separate ADD resp. PLAY or LOADBG commands especially in case of complicated templates and expensive background clips…
Maybe it is nonsense.
J

8

You are right, you can swap layers also from channel to channel.

Templates are normally made so, that they animate in and out. So it does not make sense to play (animate in) on the preview and then swap to the out, as then there is no animating in.

I see, that you still have the „DSK Fade“ workflow in your mind :smiley:. These days are long gone and today the DSK is always enabled. Templates animate in and out by themselfs. But yes, I feel a bit nostalgig now :joy: