Why doesn't setting alpha to 0 make the image completely transparent?

Hi all. As you can see in the screenshot, I have set the alpha channel to 0, but the image still looks translucent. In my understanding, alpha can control the opacity of an image independently, so why doesn’t it work in touchdesigner?

Hello,

In the channelMix you only set alpha channel to 0 not the opacity of the whole image.
Use a LevelTOP and set the Opacity to 0 in the Post tab.

thanks! but i want to set the opacity using another img’s red channel. is there any way to set oapcity using another chop node’s data?

There are multiple ways. One would be to use a MatteTOP.
Input 1 : empty image (but depends on your need.
Input 2 : your image
Input 3 : your image used for alpha

In the MatteTOP set the Matte channel to Red.

Use a LevelTOP to modulate the alpha strength using your Chop data to drive your alpha image opacity

You can also see ReorderTOP to set alpha channel of one image from one channel of another image.

Hi @woohuang,

just as a little explanation: as @Gallo is saying, the Channel Mix in your configuration only set’s the Alpha channel but the colors are not multiplied by the Alpha necessarily hence you still see them.

When controlling the Alpha channel of one texture with a color channel of another texture you can also use the Reorder TOP and then append a Math TOP which has the option to premultiply the color with the alpha channel. You can find that option on the Multi-Add parameter page under “Operation”.

hope this helps
cheers
Markus

thank you so much!!!

thank you so much!!!