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Strange alpha problem

#1

Hi,

I am totally new to vvvv, and when I wanted to create a simple ‘black becomes transparent effect’, I found the alpha_video effect. Only the strange thing is that I see the ‘visible’ part of the video twice, one of them mirrorred.

So I started editing this shader, and even with this very simple function, I see the ‘normal’ image (video or file texture), and I see the ‘mirrorred’ image shine through the first one, and it gets more visible when I decrease the alpha value.

float4 psAlpha_VideoBetween(vs2ps In): COLOR
{
//source texture lookup
float4 outColor = tex2D(SrcSamp, In.TexCd);
outColor.a = 0.8f;
return outColor;
}

Does anyone know why this happens? Is it normal, or do you think it’s a problem with my specific setup (working on a XP SP3 laptop with ATI Radeon X1250)

hello.PNG (8.7 kB)

#2

Try to open your Render with Inspektor (Ctrl-I) and set DX24 in Depth-Buffer Format…

#3

I changed it to D24X8, leaving the backbuffer format to X8R8G8B8.
(I couldn’t find DX24 as an option, only D24X8, D16, D16_lOCKABLE)

At first sight, that seems to do the trick, and it seems logical that it wouldn’t work without it. I also needed to disable clear depth buffer for it to work.

Anyway I don’t have a clue as to where this mirrored image comes from. I mean, the pixelshader doesn’t do that, and that’s the only thing I do with the texture. Do you know why I get that effect?

Is there a ‘standard’ node that simply adds an alpha-channel to a video? Because I want to combine different textures on one screen with a GROUP node, and they only behave the way I expect them to when they all have an alpha channel.

Thanks!

#4

http://vvvv.org/tiki-download_file.php?fileId=613

Is a lumakey shader, the one your using is for prepared videos with the alpha channel specified in the bottom half of the image.

#5

The one I was using has 2 modes, one that uses the lower half, and the other mode (which I used) makes everything below a certain luma value transparent, which is more or less what I need.

That doesn’t really matter since I changed it for testing, as I mentioned in an earlier post, to simply set the alpha value to 0.5

So I am still trying to figure out where the mirrored image comes from…

#6

it is possible, that the mirrored image comes from a spreaded input, transform or texture transform… have you checked all pins that they have only one vlaue?

#7

Hi,
do you have a samplepatch? Thats much easier for helping.

#8

For this example I used the RGBContrast_2 effect (for which you can find the link in an earlier post from catweasel).

The example works, but when I disable the depth and alpha buffer, or when I choose clear alpha buffer (when exactly does that happen?), I see the image twice, once mirrored, as you can see in the added right_and_wrong.png.

I would suppose that disabling the depth buffer wouldn’t add an alpha channel to my video, but that shouldn’t change the image in any way, should it?

mirrored.7z (3.8 kB)

#9

No idea what your attached file is about. No v4p patch available? MAy be including your texture?

#10

It’s a 7-zip file, unzip with http://www.7-zip.org/ or any other program supporting 7z.

It contains a v4p and a texture and an image showing what I get with alpha channel enabled and disabled.

#11

for your convenience

mirrored.zip (4.8 kB)

#12

It’s what it had to be, you seeing the backside of your’e box.
try quad instead

#13

Oh, I like to be served ;)
It was just a little thing - you took a box as input mesh. So, your texture will be put on all six sides of a box. The second mirrored image was image of back side.
For plain 2d-images best option is a mesh which is just sort of canvas. I added some toggle-switches for explaination in you patch. Play around with them to see what happens. (fill.node goes between a solid-common view, point-view and grid-view, which is nice for seeing mesh only)

edit: antokhio was faster :D

mirrored.zip (9.2 kB)

#14

Now I see where I went wrong (as you can see I didn’t quite understand what the ‘box’ node did)

Thanks guys!

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