Sobel Filtering should also compute direction. about canny-opencl

[jolson6]

It looks like the function atan2 returns values expressed in radians which would need to be a double or a float, though we could convert those values to degrees before storing them. I'm leaning towards using option 3 since it saves space using an unsigned char but still allows us to have the degrees stored as meaningful values. The only drawback I can see to this approach is that you are unable to store degrees above 255, but I don't know that a Sobel filter would ever require a direction greater than 180 degrees anyway.

[jolson6]

I was trying to add us both as assignees, but it doesn't look lil it will let two people be assigned.

[jolson6]

I suppose the other downside of using unsigned char is that we would need to typecast it as an int in order to use it as a number value. I suppose this is a trade off of space versus compute time, though I don't know how much compute effort is required to typecast something.

[smskelley]

Yeah, it appears as though Github only allows one person to be assigned to an issue.

That's a good point about atan2 returning radians, since it would then make no sense to store degrees in a float.

On the note of typecasting, I could be mistaken, but I have always assumed they are a compile time operation, so really no compute is required. Additionally, uchar and int should play nicely together without explicit casting. I guess technically adding a uchar and an int might cause one register to be zeroed before storing the uchar, but that's negligible and up to the compiler.

This discussion has so far sold me on option 3 as being a good choice. I would be interested in seeing what the performance difference between a floating point radian representation and a unsigned char degree representation, whether there is a noticeable difference or not.

I have unassigned myself from this issue. I was planning on doing it, but it doesn't matter with me. If someone else would like to do it, feel free to assign yourself. If not, I'll take care of it when I have a chance.

[jolson6]

I've been working on it today and I think I have it almost ready to test.