Set pixels with values below x to 0?

[latimeriasdream]

I am looking for something like a threshold, but with a fine control where i can say any pixels with a R value greater than 50, set the R value to 0 or some specified value. Seemed like the procedural texture made sense but i can not figure out how to do this.

[walt.farrell]

If you haven't seen these tutorials, they might help:

https://forum.affinity.serif.com/index.php?/search/&q=Procedural Absolute beginners&type=forums_topic&quick=1&nodes=9&search_and_or=and&sortby=relevancy

Or another user may be along who can help. 

[v_kyr]

6 hours ago, latimeriasdream said:

I am looking for something like a threshold, but with a fine control where i can say any pixels with a R value greater than 50, set the R value to 0 or some specified value. Seemed like the procedural texture made sense but i can not figure out how to do this.

R in the sense of red channel color value, or an x coordinate value?  - See also related ... (ah Walt already pointed to some tuts about that theme).

AFAIK and what I always see as a problem for such things is, if you can't make use of any supported conditional expressions (if/else, equals ==, >=, <= ... etc.). Thus peronally I prefer to do such things in scripting + programming languages which offer much more capabilities and flexibility in this regard.

• https://stackoverflow.com/questions/69213814/how-to-change-the-value-of-one-rgb-channel-in-python-with-cv2
• https://pythonexamples.org/python-opencv-extract-red-channel-of-image/
• https://stackoverflow.com/questions/59320564/how-to-access-and-change-color-channels-using-pil
• ... etc.

[latimeriasdream]

R as in the red channel, x just being a random number. I would like to stay in affinity instead of scripting for art direction, I want the ui and ux of affinity, not having to juggle things from the command line.

[thomaso]

21 minutes ago, latimeriasdream said:

I would like to stay in affinity instead of scripting for art direction, I want the ui and ux of affinity, not having to juggle things from the command line

Doesn't your request for "something like procedural texture" imply a kind of " juggle things from the command line"?

wikipedia: "In computer graphics, a procedural texture is a texture created using a mathematical description"

In addition to Walt's link to a bunch of tutorials done within Affinity here is one more:

[latimeriasdream]

In my case scripting is very inefficient because I'm working with fine details, a few pixels of tolerance while also needing to assign colors and develop how they look. So having  a live viewport is very important. Basically i am taking a black and white image doing things like assigning colors and detecting edges from between certain value ranges.

The procedural texture doesn't seem to have any options for conditional statements so i was hoping someone had come up with the math or another solution.

[lepr]

Set red value to 0 where red value is less than r (8-bit integer):

R = step(r/255, R)*R

 

 

 

 

Edited January 1 by lepr
noticed error in formula

[latimeriasdream]

Thank-you! This is exactly what i was looking for.