I want to play with the part of the image outside the circle , i want to put some algorithms on image area which is outside the rectangle , Can i do this task and how can i do it , which way i need to follow
And can I apply the same functionalities without drawing rectangle on the image ? mean to say not to draw the rectangle on image and leave that area for further operations , just mention its angle without drawing it
Its solution can be found here given by the #haris
Solution :
Draw your rectangle to new binary image with thickness=CV_FILLED
Invert above binary image and create mask for your interested region.
Copy the source to new Mat and perform your operation.
Finally copy the processed image to your source image using the same mask.
I don't know what process you are going to do, and if it not use the neighbor pixel like filter, the above may work fine.
Edit:
While doing filter operation using above method, the black region in the mask boundary will also consider as a neighbor, so better approach is
Create mask using your Rect.
Copy source to new Mat using above mask((the part you need to exclude).
Process the entire source.
Later copy back the region of exclusion to processed image using above mask.
Related
I would to make a part of an image black before applying the distance transform algorithm
I have tried to create a black image and use the Logic Gate functions in opencv but to no avail.
I would like to change the white region(marked with arrow) to black and then apply the distance transform algorithm :
is it possible to pass a kernel of a particular size but only with zeros? And wherever the kernel matches, replace it with a mask of a particular size but only with ones?
Im' not entirely sure by what criterion you define which part is to be made black.
If the black area is known in advance you can just use use an image of the black mask and combine them using cv::Multiply(mask, image)
If you want to automatically black out a connected white area starting from a given point you can use cv::floodFill. Details can be found here
I have a drawing application that draws many lines, polygons etc. on a device context. I'm also drawing background bitmaps that come from an external source and take a long time to load.
When drawing a new frame I first start threads that load the bitmaps, then draw my vector data, and at the end would like to draw the loaded bitmaps while preserving the vector data. I need the bitmaps "under" the vector data but I can't draw them first because they're not loaded, and waiting for them to load would slow things down a lot.
My idea was to apply the "bitmap with transparency" technique:
Copy the portion of my device context that would be covered by
the bitmap into a monochrome image, anything drawn with the
background color should be drawn on, everything else is off-limits.
Copy the image over the bitmap (with the proper ROP code) to mark
what needs to be transparent in the bitmap
StretchBlt the modified bitmap onto the device context
The bitmap needs to be transformed to fit properly on my device context, so I use SetWorldTransform to apply an affine transformation to my device context. The transformation has both a rotation and a shear.
Unfortunately, this fails at step 1 because, as per the documentation of StretchBlt:
If the source transformation has a rotation or shear, an error occurs.
Now, I did try setting the inverse transformation on my monochrome DC, which would transform my sheared data into a proper rectangle, but the function still fails.
So I guess my question is: how do I bitblit a raster image without deleting my data (a function where I give a transparent color in the destination, not the source, would be perfect), OR is there an easy way to extract the color data from a device context that has a rotate and shear transform on it?
I have video frames with elliptical objects in them. I'm trying to detect the main ellipse using regionprops and it works just fine.
However, since I want to speed up the process, I want regionprops to only look for those ellipses in a certain area of the image. I can crop the images each frame, to only have the relevant area left, but I would rather have regionprops look only in specified areas.
Is such an option possible?
Regioprops uses label matrix provided by bwlabel(bw_image) or just logical(grayscale_image) if you suppose that there is only object in the image. To make regionprops process only a part of image you should set irrelevant part of the label matrix to zero.
I've seen a few libraries that pixelate images, some of them even feature non-square shapes such as The Pixelator's circle and diamond shapes.
I'm looking however to make a particular shape, I want a "pixel" that is 19x27 px. Essentially, the image would still look pixelated but it would use tallish rectangle shapes as the pixel base.
Are there any libraries out there that do this, if not, what alterations to existing algorithms/functions would I need to make to accomplish this?
Unless I am not understanding your question, the algorithm you need is quite simple!
Just break your image up into a grid of rectangles the size you want (in this case 19x27). Loop over each section of the grid and take the average color of the pixels inside (you can simply take the average of each channel in RGB independently). Then set all of the pixels contained inside to the average color.
This would give you an image that is the same size as your input. You could of course resize your image first to a more appropriate output size.
You might want to look up convolution matrices.
In a shader, you would use your current pixel location to grab a set of nearby pixels from the original image to render to a pixel in a new buffer image.
It is actually just a slight variation of the Box Blur image processing algorithm except that instead of grabbing from the nearby pixels you would grab by the divisions of the original image relative to the 19x27 divisions of the resulting image.
I've already got my ROI(CvBOX2D type) by series of contour processing, now I just want to focus on the image part within the ROI, e.g.: feed this part into another processing function, how can I do that? I know there is CvSetImageROI, but the type is CvRect, so I should convert CvBox2D to CvRect first? Or some way to apply a mask on it with the area outside the box set to 0?
Thanks in advance!
Only axis aligned ROIs are directly supported in OpenCV (CvRect or IplROI). This is because they allow direct access to the image memory buffer.
There are 2 ways to go about working on a non-axis aligned ROI in OpenCV. Neither of them is as efficient as using axis-aligned ROIs.
Rotate your image, or bounding box, so that your ROI is now axis aligned in the resulting rotated image.
Note: the rotation will slightly blur your image.
Use a mask: Draw your ROI as a white rectangle on a black BG the same size as the image, and give your processing functions this mask as the additional parameter.
Note: not all functions support masks.
I would recommend option 1 if you really must stay within the exact bounds of your ROI. Otherwise, just use the bounding rect.
Use c++ api of opencv. seriously. do it.
cv::Rect roi = cv::RotatedRect(box).boundingRect();
Mat_<type> working_area(original_mat, roi);
// now operate on working_area
Note: this will operate on the bounding rect. I didn't find information on how to create a mask out of rotatedrect. Probably you have to do it by hand in a scanline fashion.