# Thread: direction vector of pixels

1. ## direction vector of pixels

will we be able to get the direction of pixels in an image,by means of a direction vector or something ???

2. ## Re: direction vector of pixels

Direction of a pixel? Interesting concept, individual pixels aren't generally thought of having a direction. You'll have to provide a bit more detail of what it is you mean, I think.

3. ## Re: direction vector of pixels

something like the orientation of the pixel... not very sure if such a thing will be available from an image

4. ## Re: direction vector of pixels

An orientation for a pixel makes no sense to me. A pixel is a infinitely small sample, and does not have any kind of direction.

How do you plan to use this "orientation" once you have it?

5. ## Re: direction vector of pixels

actually im trying to develop a algorithm which would help me in my work,which deals with detecting a road network from a satellite image and im using openGL for it and im relatively new to openGL.

so,i thought if there is anything like orientation,then i could use it to find the neighbouring pixel of the same or similar orientation and thus map the road stretch.

can u suggest me any other way to go abt the total process ???

6. ## Re: direction vector of pixels

Hi !

Then you would need a heightmap instead, you need to know the height of a pixel compared to the others, I guess you could use the color of a pixel to indicate the height of course.

Mikael

7. ## Re: direction vector of pixels

Sounds like an intersting problem. Not sure that anyting in OpenGL can help you with this specific problem. My first thought would be, does the color of the pixels from the road stand out enough from the other areas of the satellite image that you could use a flood-fill type of algorithm to find all pixels of a similar color?

8. ## Re: direction vector of pixels

This is a problem in computer vision. What you need to do is find the `average', `minima' and `maxima' pixels in the candidate area. From these you have an `axis' that can give you the angle of orientation of the object. Try it in your mind with an ellipse - it actually works

9. ## Re: direction vector of pixels

Explain a little more rome....

10. ## Re: direction vector of pixels

the problem is this...

a IKONOS satellite image of 1 meter resolution is given as input to the system. the user cliks a valid point on the road and the program registers this point. what i planned was to find the color values of the pixel and its depth...then parse thru all its immediate eight neighboring pixels to see if they are of similar color and depth,cos a road is almost uniformly colored.
this will continue till the road edge is reached or the image edge is reached.all the similar colored pixels can be stored in an array and later can be marked with a distinct color to show the road patch.

i brought in the depth concept,becos in few cases the pixel on the road and a pixel on the edge (a barrier or road marking) gave me the same RGB values even if they were visibly of different colors. so ,i thought maybe ,if the depth was the same ,then two distinct colored pixels wouldnt give similar RGB values.

as im jus starting up with openGL,i am stuck without knowing how to proceed after getting the pixel RGB values. any help ???

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