I am stuck at a current project:
I have an input picture showing the ground with some shapes on it. I have to find a specific shape with a given template.
I have to use distance transformation into skeletonization. My question now is: How can I compare two skeletons? As far as I noticed and have been told, the most methods from the Image Processing Toolbox to match templates don't work, since they are not scale-invariant and rotation invariant.
Also some skeletons are really showing the shapes, others are just one or two short lines, with which I couldn't identify the shapes, if I didn't know what they should be.
I've used edge detection, and region growing on the input so there are only interessting shapes left.
On the template I used distance transformation and skeletonization.
Really looking forward to some tips.
Greetings :)
You could look into convolutions?
Basically move your template over your image and see if there is a match, and where.
The max value of your array [x,y] is the location of your object in the image.
Matlab has a built-in 2D convolution function for this
Related
Given are two monochromatic images of same size. Both are prealigned/anchored to one common point. Some points of the original image did move to a new position in the new image, but not in a linear fashion.
Below you see a picture of an overlay of the original (red) and transformed image (green). What I am looking for now is a measure of "how much did the "individual" points shift".
At first I thought of a simple average correlation of the whole matrix or some kind of phase correlation, but I was wondering whether there is a better way of doing so.
I already found that link, but it didn't help that much. Currently I implement this in Matlab, but this shouldn't be the point I guess.
Update For clarity: I have hundreds of these image pairs and I want to compare each pair how similar they are. It doesn't have to be the most fancy algorithm, rather easy to implement and yielding in a good estimate on similarity.
An unorthodox approach uses RASL to align an image pair. A python implementation is here: https://github.com/welch/rasl and it also
provides a link to the RASL authors' original MATLAB implementation.
You can give RASL a pair of related images, and it will solve for the
transformation (scaling, rotation, translation, you choose) that best
overlays the pixels in the images. A transformation parameter vector
is found for each image, and the difference in parameters tells how "far apart" they are (in terms of transform parameters)
This is not the intended use of
RASL, which is designed to align large collections of related images while being indifferent to changes in alignment and illumination. But I just tried it out on a pair of jittered images and it worked quickly and well.
I may add a shell command that explicitly does this (I'm the author of the python implementation) if I receive encouragement :) (today, you'd need to write a few lines of python to load your images and return the resulting alignment difference).
You can try using Optical Flow. http://www.mathworks.com/discovery/optical-flow.html .
It is usually used to measure the movement of objects from frame T to frame T+1, but you can also use it in your case. You would get a map that tells you the "offset" each point in Image1 moved to Image2.
Then, if you want a metric that gives you a "distance" between the images, you can perhaps average the pixel values or something similar.
I've designed an algorithm that matches correspondent lines seen from different positions of a robot.
Now I want to merge correspondent lines into one.
Does anyone know an algorithm for this purpose?
It seems like what you're trying to do is a mosaic but restricted to 2D. Or at least something similar considering only extracted features. I'll go through the basic idea of how to do it (as I remember it anyway).
You extract useful features in both images (your lines)
You do feature matching (your matching)
You extract relative positional information about your cameras from the matched features. This allows to determining a transform between the two.
You transform one image into the other's perspective or both to a different perspective
Since you say you're working in a 2D plane that's where you will want to transform to. If your scans can be considered to not add any 3D distortion (always from the same hight facing perpendicular to the plane) then you need only deal with 2D transformations.
To do what you call the merging of the lines you need to perform step 3 and 4 of the mosaic algorithm.
For step 3 you will need to use a robust approach to calculate your 2D Transformation (rotation and translation) from one picture/scan to the other. Probably something like least mean squares (or other approaches for estimating parameters from multiple values).
For step 4 you use the calculated 2D transform and possibly a previous transformation that was calculated for the previous picture (not needed if you're matching from the composed image, a.k.a moasic, to a new image instead of sequetial images) use it on the image it would apply to. In your case probably just your 2D lines from the new scan (and not a full image) will need to be transformed by this global 2D transform to take their position and orientation to the global map reference.
Hope this helps. Good Luck!
I have several binary images which represent a partial map of an area (~4m radius) and were taken ~0.2m apart, for example:
(Sorry for the different axis limit).
If you look closely, you'll see that the first image is about 20cm to the right.
I want to be able to create a map of the area from several pictures like this.
I've tried several methods, such as Matlab's register but couldn't find any good algorithm for this purpose. Any ideas on how to approach this?
Thanks in advance!
Two possible routes:
Use imregister. This does registration based on image intensity. You will probably want a rigid transform.
However, this will require your data to be an image (matrix), which it doesn't look like it currently is.
Alternatively, you can use control points. These are common (labelled) points in each image which provide a reference to determine the transform.
Matlab has a built in function to determine control points, cpselect. However, again this requires image data. You may be better of writing your own function to do this or just selecting control points manually.
Once you have control points you can determine the transform between them using fitgeotrans
Can anyone guide me how the function 'hough transform' works in matlab?? The problem is that i have an image containing two straight rectangles and one rectangle is tilted at some angle. According to me after applying hough transform; i should get a line structure of 1X6 but i am getting a structure of 1x14. Can anyone help me? I have also uploaded the images:
You can't restrict Hough Transform to give a structure of 1x6.It doesn't produce stabile results.It also doesn't work well when looking further ahead on curved roads. I should not acquire 1x6 structure from each frame.Instead, I should take all returned line segments and use some logic to determine the lane markings.
First of all, your image actually looks slightly blurred. I don't know if it actually is , but if so, you need to run an edge detection algorithm, so your hough transform does not detect the blurred part of the line.
Second of all, you need to reduce the number of detected lines, simply by taking out any lines which does not have enough points going through it. This can be done by thresholding the H variable in [H,t,r]=hough(image).
Additional Sources:
http://en.wikipedia.org/wiki/Hough_transform
http://www.mathworks.com/help/toolbox/images/ref/hough.html
I am able to draw shapes using the UIBezierPath object. Now I want to identify different shapes drawn using this eg. Rectangle , Square , Triangle , Circle etc. Then next thing I want to do is that user should be able to select a particular shape and should be able to move the whole shape to different location on the screen. The actual requirement is even more complex , but If I could make this much then I can work out on the rest.
Any suggestion or links or points on how do I start with this is welcome . I am thinking of writing a separate view to handle every shape but not getting how do I do that..
Thank You all in advance !!
I recommend David Gelphman’s Programming with Quartz.
In his chapter “Drawing with Paths” he has a section on “Path Construction Primitives” which provides a crossroads:
If you use CGContextAddLineToPoint your user could make straight lines defined by known Cartesian points. You would use basic math to deduce the geometric shapes defined by those points.
If you use CGContextAddCurveToPoint your user could make curved lines defined by known points, and I’m pretty sure that those lines would run through the points, so you could still use basic math to determine at least an approximation of the types of shapes formed.
But if you use CGContextAddQuadCurveToPoint, the points define a framework outside of the drawn curve. You’d need more advanced math to determine the shapes formed by curves along tangents.
Gelphman also discusses “Path Utility Functions,” like getting a bounding box and checking whether a given point is inside the path.
As for moving the completed paths, I think you would use CGContextTranslateCTM.