i need to make a program where i have to detect the edge of a subimage (like a face in a portrait) using canny detector. then i need to filter that portion out and paste it in another background. it is like mixing 2 layers. can anybody give me any algorithm for this? or any idea about the process?
You are probably aware that the task of selecting a subimage is most known Region of Interest (ROI).
Edge detection with canny shouldn't be a problem since OpenCV implements it as cvCanny().
For what I understand you want to overlap two images. I suppose you want to add one image on top of each other? Take a look at step 2 on the first link I suggest: Adding Two Images with Different Size
If you want to BLEND them, then check these instructions. I have used them before to draw over the webcam window.
Related
I am trying to create a bounding box around each character in an image. I have converted the image to binary and thresholded it but I don't understand how to create a bounding box despite reading the manual.
There are a few options for the bounding box technique, but I think you'll get a great result combining these two:
First, use the technique demonstrated here to detect a large portion of text and put a bounding rectangle around it so you crop the image to this area;
Second, experiment with the technique recently presented by OpenCV, also demonstrated here. It could be used to locate/extract individual characters on the resulting image of the first step.
I suppose you are trying to implement the OCR mechanism yourself instead of relying on great APIs such as Tesseract.
If you are looking for more information on how to do digit/text recognition, check this answer.
As said before "rudely", I encourage you to rewrite your question with more detail on what you already did. We didn't understand what you would like to do. If character recognition is what you want, have a look at this.
I am new to OpenCV so I apologize if I use incorrect terminology. I am writing a program in C that finds objects in an image (in this case red building blocks) and extracts that part of the image and displays it as a new image. I have thresholded the image to remove everything but red and used cvDilate to blur the results slightly to make the object more distinct. I then used the OpenCV Contour finding and drawing functions to locate and draw the blocks.
How can I access the contour locations stored as CvSeq* and take the upper-most and lower-most contour values from a cluster of contours (there may still be some noise from other red objects) so that I can make a bounding box around it?
Thanks
Actually, you don't have to do this manually because OpenCV provides this type of functionality for you.
Look at the cvMinAreaRect2 and cvBoundingRect. Here are their examples respectively: minarea.c (has some debugging stuff, but should give you the gist of how to use it) and generalContours_demo1.cpp (in C++, but should be easy to translate).
As a side note, I would definitely suggest using the C++ API of OpenCV as it is a bit easier to understand and has more features. Also, you spend a lot less time/code worrying about memory management since the Mat class handles that for you.
Hope that helps!
I'm trying to write an CAD-like application in WPF(.NET 4.0) that needs to be able to display a lot of 2D points/lines. It will be used to display CAD-plans of entire cities with zoom, pan, rotate and point snapping on mouseover.
Right now I purely use WPF. I read the objects from the CAD file draw them into a StreamGeometry, use it as stroke of a new Path and add it to a Canvas, with several transforms.
My problem is that this solution doesn't scale well enough. It works fine with small CAD-files, but when I want to display like half a city(with houses and land boundaries) it is very very delayed.
I also tried to convert my CAD-file to an image, but
- a resolution a 32000x32000 is sometimes not enough
- when zooming out the lines are too thin.
In the end I need to be able to place this on a Canvas(2D/3D) as background.
What are my best options here?
Thanks,
Niklas
wpf is not good for a large 3d models. im afraid it is too slow. Your best bet is direct 3d or openGL
However, even with the speed of direct3d,openGL you will still need to work out how to cull as many polygons/vertices as possible before the rendering of the scene if you are trying to show an entire city.
there is a large amount of information on this (generally under game development)
there are a few techniques including frustrum culling, near and far plane culling.
also, since you probably have a static scene you may be able to use binary spacial partitioning.
As I understand the subject is 2D CAD system within WPF.
Great! I use it...
OpenGL and DirectX are in infinite loop OnDraw always. The CPU works all the time.
WPF/Silverlight 2D is smart model.
Yes, total amount of elements (for example, primitives inherited from Shape) must be not so much. But how many?
I tested own app (Silverlight). WPF will be a bit faster I hope...
Here my 2D CAD results. Performance is still great. Each beam consists of multiple primitives.
Use a VirtualCanvas like this one from Chris Lovett.
I have a sequence of images taken from a camera. The images consists of hand and surroundings. I need to remove everything except the hand.
I am new to Image processing. Would anyone help me in regard with the above Question. I am comfortable using C and Matlab.
A really simple approach if you have a stationary background and a moving hand (and quite a few images!) is simply to take the average of the set of images away from each image. If nothing else, it's a gentle introduction to Matlab.
The name of the problem you are trying to solve is "Image Segmentation". The Wikipedia page here: wiki is a good start.
If lighting consistency isn't a problem for you, I'd suggest starting with simple RGB thresholding and see how far that gets you before trying anything more complicated.
Have a look at OpenCV, a FOSS library for computer vision applications. Specifically, see the Video Surveillance module. For a walk through of background subtraction in MATLAB, see this EETimes article.
Can you specify what kind of images you have. Is the background moving or static? For a static background it is a bit straightforward. You simply need to subtract the incoming image from the background image. You can use some morphological operations to make it look better. They all depend on the quality of images that you have. If you have moving background I would suggest you go for color based segmentation. Convert the image to YCbCr then threshold appropriately. I know there are some papers available on it(However I dont have time to locate them). I suggest reading them first. Here is one link which might help you. Read the skin segmentation part.
http://www.stanford.edu/class/ee368/Project_03/Project/reports/ee368group08.pdf
background subtraction is simple to implement (estimate background as average of all frames, then subtract each frame from background and threshold resulting absolute difference) but unfortunately only works well if 1. camera has manual gain and exposure 2. lighting conditions do not change 3.background is stationary. 4. the background is visible for much longer than the foreground.
given your description i assume these are not the case - so what you can use - as already pointed out - is colour as a means of segmenting foreground from background. as it's a hand you are trying to isolate best bet is to learn the hand colour. opencv provides some means of doing this. if you want to do this yourself you just get the colour of some of the hand pixels (you would need to specify this manually for at least one frame) and convert them to HUE (which encapsulates the colour in a brightness independen way. skin colour has a very constant hue) and then make a HUE histogram. compare this to the rest of the pixels and then decided if the hue is simmilar enough.
Now that <BevelBitmapEffect> (amongst other effects) has been depreciated, I'm looking to see how I could re-create the exact same thing in a Shader Effect (including it's properties of BevelWidth, EdgeProfile, LightAngle, Relief and Smoothness).
I'm somewhat familar with pixel shading, mostly just colors manipulation of the whole image/element in Shazzam, but how to create a bevel elludes me. Is this a vertex shader and if so, how would I get started? I have searched high and low on this but can't seem to find an inkling of information that would allow me to get started in reproducing <BevelBitmapEffect> in a custom Effect.
Or, based on a comment below, is this 3D in WPF and if so, are there code libraries out there for recreating a <BevelBitmapEffect> that mimics the one that came with previous versions of WPF?
To create the bevel you need to know the distance from the edge for each pixel (search in all directions until alpha=0). From this you can calculate the normal then shade it (see silverlight example). As you mentioned there isn't much content about bevels but there are some good resources if you search for bump mapping/normal mapping to which the shading is similar. In particular this thread has a Silverlight example using a pre-calculated normal map.
To do everything in hardware ideally you would use a multipass shader, WPF's built-in effects are multipass but it doesn't allow you to write your own.
To workaround this limitation:
You could create multiple shaders and nest your element in multiple controls applying a different effect to each one.
Target WPF 4.0 and use Pixel Shader 3.0, for the increased instruction count. Although this may be a too high a hardware requirement and there is no software fallback for PS 3.0
Do some or all of the steps in software.
Without doing one of these you'd be lucky to do a 3 or 4 pixel bevel before you reach the instruction limit as the loops needed to find the distance increase the instruction count quickly.
New Sample
Download. Here is an example that uses PixelShader 3.0. It uses one shader to find the distance (aka height) to the edge, another (based on the nvidia phong shaders) is used to shade it. Bevel profiles are created by adjusting input height either with code or a custom profile can be used by supplying a special texture. There are some other features to add but it seems easily performant enough to animate the properties. Its lacking in comments but I can explain parts if needed.
There's a great article by Rod Stephens on DevX that shows how to use System.Drawing to create the WPF effects (the ones that used to exist, such as Bevel) and more. You've gotta register to view the article though, it's at http://www.devx.com/DevXNet/Article/45039. Downloadable source code too.