Hi there, this is my first topic in this forum. Here is my problem:
I've done a tracking with syntheyes and export it to houdini, than made some spikes on the trackers. But what I want is to have the spikes only on the lightest pixels of the image, so basically get ride of the trackers where the pixels are dark. I've imported my background image in COP to make it black and white and I know there's the pic() expression function to return the pixel values, but how do I use it to remove my trackers?
Here's an example of my scene if can help.
Thanks in advance.

Hi,
interesting problem, that can be solved > transfer the colour from the map to your points > convert that colour to a HSV in vops , then create an attribute based on the v ( Value ) of each of points colour. From there on you can cull points , create new attributes. etc.

rob

check your file i reuploaded it should be fixed in a very simple way
i hope i understood well your matter.
make sure the path of your pic on the vopsop is right, when i open your file the picture came with $F4 in the name at the end, make sure you choose file without “choose sequence as on entry” ticker

So all i did is group you points based on color ($CR)
and then choose that group in your copy node

i just read your post again
the expression i did is $CR<0.5 u get the group to choose the darkest points..simply invers $CR>0.5 (or whatever value you want) to select the lightest point

Thanks everyone for the replies. I've really appricieted the file you uploaded Sami, that was what I was looking for, and it's actually really simple to do, thank you again