Hi all.
I'm wondering if there is a way to get brightest and darkest RGB values in COP context.
I searched and found this thread without any clear answer: http://forums.odforce.net/topic/3417-brightest-point-in-image/ [forums.odforce.net]
Any ideas?
Thanks.

Hi Nima,

in SOPs attribute promote has methods for getting the highest and lowest value of an attribute. I promoted the results to detail and imported them to COPs inside a VOP COP2 filter.

Hello Konstantin Magnus.
Really thanks for your help.
This method works fine when your image has low resolution.
My image has resolution of 3200 by 2400 and definitely it's not a good way to create a grid in that resolution in SOP!
I am just thinking about doing this in chop.

Why dont you scale it down in COPs then? Or change the grid´s expression to something like

I'm afraid of losing one of max or min pixels during scale down process.

Well, I dont know what you are working on of course, but on a large photo I dont think it would be noticeable.

On the contrary scaling would reduce image errors and noise.

Dear Konstantin Magnus, I wanna divide color of each pixel to color of brightest pixel in image.
This is away more efficient than do it in SOP so I'm looking for a solution to do this in cop itself.

I guess you have to loop through all pixels using either VOPs or python then.

http://www.sidefx.com/docs/houdini/hom/pythoncop [www.sidefx.com]

Really Thanks.
I will take a look at that.

With Houdini 16 you can import an image into SOPs as a volume slice in addition to as meshes.

Put a COP Network down in SOPs, point it to your COP network, then set it to Volume Slice.

Then you can use Volume Reduce in Max or Min mode to put the resulting max/min into detail attributes.

You'll notice this generates different results than the attribfrommap solution - I suspect it is mis-applying linearlization somewhere. The volume solution seems correct.

You can also do this entirely in COPs.

Dilate/erode will act as a maximum/minimum in a square region depending on sign of the operation. Ideally you could just set this to 3200 for your 3200x3200 image, but because COPs tries to compute the overscan this gets too expensive. So instead do two passes. First dilate/erode by 128. Then scale by 1/64 which will be safe - you won't miss any max/mins because each max/min already got spread everywhere in 128 tiles. Now do another dilate/erode and get a solid patch of colour for use elsewhere in COPs.

Your HIP file is exactly what I want.
Thank you so much Jeff.

One last thing how can I tweak C.r, C.g and C.b attributes?
I try to tweak them in a volume wangle but VEX gives me error.
I also change them to Cd.r, Cd.g and Cd.b with the help of name node but just get completely white image!