Do webcams use overlay?

[Guest]

Archived from groups: rec.video.desktop (More info?)

Hi all,

After a quick google search, it looks like this forum is the most
appropriate place to ask. I would like to know if most webcams use
overlay.

I was planning to paint a purple rectangle in a MatLab window (doesn't
mater what MatLab is, it could be Photoshop) and was wondering whether
I would see the video captured with a webcam.

Thanks in advance,
Tony

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

<braintest@gmail.com> wrote ...
> After a quick google search, it looks like this forum is the most
> appropriate place to ask. I would like to know if most webcams use
> overlay.
>
> I was planning to paint a purple rectangle in a MatLab window (doesn't
> mater what MatLab is, it could be Photoshop) and was wondering whether
> I would see the video captured with a webcam.

I have no idea what you are asking here (and likely others don't,
either). Try it again from the top with a bit more detail.

In particular define what YOU mean by "overlay", and what a
purple rectangle has to do with anything. And what do you mean
by "captured with a webcam"?

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

"Richard Crowley" <rcrowley7@xprt.net> wrote in message
news:10rsubmntluvh66@corp.supernews.com...
> <braintest@gmail.com> wrote ...
> > After a quick google search, it looks like this forum is the most
> > appropriate place to ask. I would like to know if most webcams use
> > overlay.
> >
> > I was planning to paint a purple rectangle in a MatLab window (doesn't
> > mater what MatLab is, it could be Photoshop) and was wondering whether
> > I would see the video captured with a webcam.
>
> I have no idea what you are asking here (and likely others don't,
> either). Try it again from the top with a bit more detail.
>
> In particular define what YOU mean by "overlay", and what a
> purple rectangle has to do with anything. And what do you mean
> by "captured with a webcam"?

If the cam uses overlays then the purple (magenta) rectangle is the colorkey
for the video. I.E. anything that is the colorkey color allows the video to
show through. The details of his implementation are unimportant except to
answer the question . It's hard to know because every application can do
things differently. And since we don't know what application he is using
it's difficult to answer the question with anything but... try it yourself
and find out.

The overlay is a special video surface apart from the primary video that you
normally see. It can be sized and moved like a window. It is seen whenever
the primary surface is painted with the colorkey. The webcam itself doesn't
use the overlay plane. The software that is running the webcam does. With
directx you have VMR (Video Mixing Renderer) which can mix multiple video
images and paint them on the primary surface. That would be a case of not
using overlays. Overlays are typically limited to a single video.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

"FLY135" wrote ...
> "Richard Crowley" wrote ...
>> In particular define what YOU mean by "overlay", and what a
>> purple rectangle has to do with anything. And what do you mean
>> by "captured with a webcam"?
>
> If the cam uses overlays then the purple (magenta) rectangle
> is the colorkey for the video. I.E. anything that is the colorkey
> color allows the video to show through.

Yes, I understand what chroma-keying (not "colorkey") is.
But the question was sufficiently diffuse and undefined that
the OP seems unlikely to get any useful response.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

"Richard Crowley" <rcrowley7@xprt.net> wrote in message
news:10ru2dunar3q915@corp.supernews.com...
> "FLY135" wrote ...
> > "Richard Crowley" wrote ...
> >> In particular define what YOU mean by "overlay", and what a
> >> purple rectangle has to do with anything. And what do you mean
> >> by "captured with a webcam"?
> >
> > If the cam uses overlays then the purple (magenta) rectangle
> > is the colorkey for the video. I.E. anything that is the colorkey
> > color allows the video to show through.
>
> Yes, I understand what chroma-keying (not "colorkey") is.
> But the question was sufficiently diffuse and undefined that
> the OP seems unlikely to get any useful response.

Your response indicated that you didn't know what overlay was and didn't
understand the significance of the purple color. I explained that.

"Yes, I understand what chroma-keying (not "colorkey") is."

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/directshow/htm/colorkeystructure.asp

Don't get caught up trying to correct peoples terminology.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

"FLY135" <fly_135(@ hot not not)notmail.com> wrote in message news:%fEvd.4822$Yj4.3078@newsread3.news.atl.earthlink.net...
<snip>
> Don't get caught up trying to correct peoples terminology.
>
It's generally considered to be bad form to correct grammar and
spelling errors in newsgroup posts, provided the meaning is clear.
But in a technical area like video, people need to learn proper
terminology, especially when their meaning isn't clear otherwise.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

"L David Matheny" <ldmnews1@netassoc.net> wrote in message
news:328kr2F3gpmlaU1@individual.net...
> "FLY135" <fly_135(@ hot not not)notmail.com> wrote in message
news:%fEvd.4822$Yj4.3078@newsread3.news.atl.earthlink.net...
> <snip>
> > Don't get caught up trying to correct peoples terminology.
> >
> It's generally considered to be bad form to correct grammar and
> spelling errors in newsgroup posts, provided the meaning is clear.
> But in a technical area like video, people need to learn proper
> terminology, especially when their meaning isn't clear otherwise.

The proper terminology was just what I used. It's colorkey and not chroma
key. There is a difference if you want to get technical. In that
colorkeying is done by specifying the RGB color and applicable to computer
video surfaces. Chroma keying is done in video production specifying the
Chroma color.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

"FLY135" <fly_135(@ hot not not)notmail.com> wrote in message
newscFvd.4861$Yj4.179@newsread3.news.atl.earthlink.net...
>
> The proper terminology was just what I used. It's colorkey and not chroma
> key. There is a difference if you want to get technical. In that
> colorkeying is done by specifying the RGB color and applicable to computer
> video surfaces. Chroma keying is done in video production specifying the
> Chroma color.
>
I'm not sure, but Chromakey may be the product name for Grass Valley's
color keying option used in their switchers for many years. The term is
often used generically (like Kleenex, Scotch tape, etc.). They had one of
the few color keying schemes that sort of worked with composite video
(they also had a pretty good RGB keyer).

David

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

"david.mccall" <david.mccallUNDERLINE@comcast.net> wrote in message
news:TuFvd.569337$D%.383275@attbi_s51...
>
> "FLY135" <fly_135(@ hot not not)notmail.com> wrote in message
> newscFvd.4861$Yj4.179@newsread3.news.atl.earthlink.net...
> >
> > The proper terminology was just what I used. It's colorkey and not
chroma
> > key. There is a difference if you want to get technical. In that
> > colorkeying is done by specifying the RGB color and applicable to
computer
> > video surfaces. Chroma keying is done in video production specifying
the
> > Chroma color.
> >
> I'm not sure, but Chromakey may be the product name for Grass Valley's
> color keying option used in their switchers for many years. The term is
> often used generically (like Kleenex, Scotch tape, etc.). They had one of
> the few color keying schemes that sort of worked with composite video
> (they also had a pretty good RGB keyer).

Regardless, whether someone used the term chroma key or colorkey I would
know what they meant. It just so happens that wrt keying the overlay
surface in the windows windows environment, the term colorkey is prevalent
in MS programming documentation and API naming since VFW days. It's hardly
a point worth debating. I was simply addressing Richard's post indicating
that he was unfamiliar with the concept of overlays and the purple
reference. A simple thanks would have been better than an erroneous
correction.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

"FLY135" wrote ...
> Regardless, whether someone used the term chroma key or colorkey I would
> know what they meant. It just so happens that wrt keying the overlay
> surface in the windows windows environment, the term colorkey is prevalent
> in MS programming documentation and API naming since VFW days. It's
> hardly
> a point worth debating. I was simply addressing Richard's post indicating
> that he was unfamiliar with the concept of overlays and the purple
> reference. A simple thanks would have been better than an erroneous
> correction.

The fact that you think I am unfamiliar with chroma-keying (or "color-
keying" as Microsoft has chosen to continue the coloquialism) is
indicitave of how far you have missed the whole point. I have worked
with Pantone Colorkey before the days of color television, and with
chroma-keying in video before the days of computers. While I spend
most of my paid hours writing code for MS Windows, I don't consider
the colossus of Bellevue to be the last word on terminology. If you
wish to continue this pointless thread I'll leave you to it. Bye.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

I only think you are unfamiliar with what you state you are unfamiliar with.
As demonstrated by your statement...

"In particular define what YOU mean by "overlay", and what a purple
rectangle has to do with anything."

Bye.

"Richard Crowley" <rcrowley7@xprt.net> wrote in message
news:10rue16726olkb7@corp.supernews.com...
> "FLY135" wrote ...
> > Regardless, whether someone used the term chroma key or colorkey I would
> > know what they meant. It just so happens that wrt keying the overlay
> > surface in the windows windows environment, the term colorkey is
prevalent
> > in MS programming documentation and API naming since VFW days. It's
> > hardly
> > a point worth debating. I was simply addressing Richard's post
indicating
> > that he was unfamiliar with the concept of overlays and the purple
> > reference. A simple thanks would have been better than an erroneous
> > correction.
>
> The fact that you think I am unfamiliar with chroma-keying (or "color-
> keying" as Microsoft has chosen to continue the coloquialism) is
> indicitave of how far you have missed the whole point. I have worked
> with Pantone Colorkey before the days of color television, and with
> chroma-keying in video before the days of computers. While I spend
> most of my paid hours writing code for MS Windows, I don't consider
> the colossus of Bellevue to be the last word on terminology. If you
> wish to continue this pointless thread I'll leave you to it. Bye.
>
>

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

Sorry I wasn't clear. When you watch a DVD, if you hit the
"PrintScreen" key, you won't see the movie but a purple rectangle
instead. The DVD decoding hardware bypasses the video card and displays
the actuall movie wherever there is a certain color (here, purple).
I was wondering whether webcams were doing the same thing.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

<braintest@gmail.com> wrote ...
> Sorry I wasn't clear. When you watch a DVD, if you hit the
> "PrintScreen" key, you won't see the movie but a purple rectangle
> instead. The DVD decoding hardware bypasses the video card and displays
> the actuall movie wherever there is a certain color (here, purple).
> I was wondering whether webcams were doing the same thing.

Likely no generic answer to that. Depends on the particular software
and likely the video display hardware and drivers as well.

Lots of DVD player software writes directly to the video card
memory and bypasses the normal Windows video drivers. That
is why you don't see the picture when you connect an external
monitor or use PrintScreen.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

<braintest@gmail.com> wrote in message
news:1103162360.747766.149030@z14g2000cwz.googlegroups.com...
> Sorry I wasn't clear. When you watch a DVD, if you hit the
> "PrintScreen" key, you won't see the movie but a purple rectangle
> instead. The DVD decoding hardware bypasses the video card and displays
> the actuall movie wherever there is a certain color (here, purple).
> I was wondering whether webcams were doing the same thing.

Depends on the capture program. I just tried it with Microsoft MovieMaker
and my Dlink web cam and it didn't use overlays. I think with VMR7/9 in
DirectShow you will be seeing less use of the overlay as time goes on.