I get a mat (320x480) from the camera of the phone. Then I need to process a part of that frame. I use ROI for that:
mat2 = new Mat(width, 175, CvType.CV_8SC3);
Rect roi = new Rect(75, 0, 175, 320);
mat2 = new Mat(mat1, roi);
Now I want to create a new mat with dimensions 320x480 with a black background. How do I do that?
Then I want to copy the processed ROI to the new mat at the same place it was on the first mat. How do I do that?
I am using OpenCV 3.4.6 and android studio.
Thank you in advance
You just need to submat() an ROI from the original Mat (your camera frame), and then process the submat as a normal Mat, but be careful to do not clone the sumbmat if you want the original get the effect.
Update according to the comment:
Mat originalMat = someMat;
Mat blackMat = Mat.zeros(size, CvType.CV_8UC1); // it is your black mat
// create a submat from the original mat, and clone it
Mat roiMat = originalMat.submat(rect).clone();
..... // do what you want with roiMat
// now copy the result to the original mat
Mat dst = originalMat.submat(rect); // do not clone this submat
roiMat.copyTo(dst);
// done!
Related
I am using OpenCV android library thresholding method for image segmentation, but the problem is that the output bitmap contains black background which I do not want please note that original image does not have any black background it is actually white. I am attaching the code for your reference, I am new to opencv and don't have much understanding about it also so kindly help me out.
private void Segmentation() {
Mat srcMat = new Mat();
gray = new Mat();
Utils.bitmapToMat(imageBmp, srcMat);
Imgproc.cvtColor(srcMat, gray, Imgproc.COLOR_RGBA2GRAY);
grayBmp = Bitmap.createBitmap(imageBmp.getWidth(), imageBmp.getHeight(), Bitmap.Config.RGB_565);
Utils.matToBitmap(gray, grayBmp);
grayscaleHistogram();
Mat threshold = new Mat();
Imgproc.threshold(gray, threshold, 0, 255, Imgproc.THRESH_BINARY_INV + Imgproc.THRESH_OTSU);
thresBmp = Bitmap.createBitmap(imageBmp.getWidth(), imageBmp.getHeight(), Bitmap.Config.RGB_565);
Utils.matToBitmap(threshold, thresBmp);
Mat closing = new Mat();
Mat kernel = Mat.ones(5, 5, CvType.CV_8U);
Imgproc.morphologyEx(threshold, closing, Imgproc.MORPH_CLOSE, kernel, new Point(-1, -1), 3);
closingBmp = Bitmap.createBitmap(imageBmp.getWidth(), imageBmp.getHeight(), Bitmap.Config.RGB_565);
Utils.matToBitmap(closing, closingBmp);
result = new Mat();
Core.subtract(closing, gray, result);
Core.subtract(closing, result, result);
resultBmp = Bitmap.createBitmap(imageBmp.getWidth(), imageBmp.getHeight(), Bitmap.Config.RGB_565);
Utils.matToBitmap(result, resultBmp);
Glide.with(ResultActivity.this).asBitmap().load(resultBmp).into(ivAfter);
}
enter image description here
What exactly do you want it to be then? Binary thresholding works like this:
if value < threshold:
value = 0
else:
value = 1
Of course you can convert it to a grayscale / RGB image and adjust the background to your liking. You can also invert your image (white background, black segmentation) by using the ~ operator.
segmented_image = ~ segmented_image
Edit: OpenCV has a dedicated flag to invert the results: CV_THRESH_BINARY_INV You are already using it, maybe try changing it to CV_THRESH_BINARY
I want to adjust the brightness of frame in opencv camera which is called mRgba. After I split the channel of lab. I hope to adjust the L channel but I don't know how to change the value in the L channel.
Mat lab_image = new Mat();
//mRgba is the frame which shows in the camera
Imgproc.cvtColor(mRgba, lab_image, Imgproc.COLOR_mRGBA2RGBA);
Imgproc.cvtColor(lab_image, lab_image, Imgproc.COLOR_RGBA2RGB);
Imgproc.cvtColor(lab_image, lab_image, Imgproc.COLOR_RGB2Lab);
// Extract the L channel
List<Mat> lab_list = new ArrayList(3);
Core.split(lab_image,lab_list);
//lab_list.get(0).copyTo(mRgba);
Mat result_image = new Mat();
Core.merge(lab_list,result_image);
Imgproc.cvtColor(result_image, mRgba, Imgproc.COLOR_Lab2RGB);
Imgproc.cvtColor(mRgba, mRgba, Imgproc.COLOR_RGB2RGBA);
Imgproc.cvtColor(mRgba, mRgba, Imgproc.COLOR_RGBA2mRGBA);
I try to use setTo() to set the color but it change the whole color.
lab_list.get(0).setTo(new Scalar(255,255,255,0.1));
I want to add value to increase the whole brightness.I hope the final result can become the following photo. Please give me some help. Thank You.
http://i.stack.imgur.com/dSr4L.png
Let us say you want to increase your L channel by 50.
You can do it like this:
Mat dst = new Mat();
Core.add(lab_list.get(0), Scalar(50), dst);
lab_list.set(0, dst);
And then merge the channels like you do already.
> Hi, I am using OpenCV android library grabcut() method to extract an image from background, but the problem is that the output bitmap contains background Same as original image and object become white .I need Object as its same as original image and background transparent
I am using this code
private static Bitmap makeBlackTransparent(Bitmap image) {
// convert image to matrix
Mat src = new Mat(image.getWidth(), image.getHeight(), CvType.CV_8UC4);
Utils.bitmapToMat(image, src);
// init new matrices
Mat dst = new Mat(image.getWidth(), image.getHeight(), CvType.CV_8UC4);
Mat tmp = new Mat(image.getWidth(), image.getHeight(), CvType.CV_8UC4);
Mat alpha = new Mat(image.getWidth(), image.getHeight(), CvType.CV_8UC4);
// convert image to grayscale
Imgproc.cvtColor(src, tmp, Imgproc.COLOR_BGR2GRAY);
// threshold the image to create alpha channel with complete transparency in black background region and zero transparency in foreground object region.
Imgproc.threshold(tmp, alpha, 100, 255, Imgproc.THRESH_BINARY);
// split the original image into three single channel.
List<Mat> rgb = new ArrayList<Mat>(3);
Core.split(src, rgb);
// Create the final result by merging three single channel and alpha(BGRA order)
List<Mat> rgba = new ArrayList<Mat>(4);
rgba.add(rgb.get(0));
rgba.add(rgb.get(1));
rgba.add(rgb.get(2));
rgba.add(alpha);
Core.merge(rgba, dst);
// convert matrix to output bitmap
Bitmap output = Bitmap.createBitmap(image.getWidth(), image.getHeight(), Bitmap.Config.ARGB_8888);
Utils.matToBitmap(dst, output);
return output;
}
There are 2 problems in your code:
Firstly you need to segment out the white background, so adjust your thresh to be near 220 - 240 and also use THRESH_BINARY_INV instead of THRESH_BINARY :
Imgproc.threshold(tmp, alpha, 230, 255, Imgproc.THRESH_BINARY_INV);
Secondly, you must pre-multiply the ARGB layers, as Android ImageView behaves weird without premultiplication, for that you need to use cvtColor with COLOR_RGBA2mRGBA flag:
// Create the final result by merging three single channel and alpha(BGRA order)
List<Mat> rgba = new ArrayList<Mat>(4);
rgba.add(rgb.get(0));
rgba.add(rgb.get(1));
rgba.add(rgb.get(2));
rgba.add(alpha);
Core.merge(rgba, dst);
Imgproc.cvtColor(dst, dst, Imgproc.COLOR_RGBA2mRGBA);
I started with the following image, named rgbaMat4Mask.bmp:
Then I converted it to HSV, and then did inRange() to find contours, and got the following Mat named maskedMat:
Then I went on to draw the first contour (the bigger one), on a newly created empty Mat named newMatWithMask, which has been given the same size as that of the first image I started with:
So far so good, but the problem starts now. I created a new Mat and gave it the same size as that of the first contour (the bigger one), and then set its background color to new Scalar(120, 255, 255). Then I copied the newMat4MaskFinished to it using copyTo function. But neither is the size of the resulting Mat same as that of the contour, nor is its background color set to new Scalar(120, 255, 255) which is blue.
It is rather an image with size same as that of the entire mask, and has a black background. why? What am I doing wrong?
public void doProcessing(View view) {
// READING THE RGBA MAT
Mat rgbaMat4Mask = Highgui.imread("/mnt/sdcard/DCIM/rgbaMat4Mask.bmp");
// CONVERTING TO HSV
Mat hsvMat4Mask = new Mat();
Imgproc.cvtColor(rgbaMat4Mask, hsvMat4Mask, Imgproc.COLOR_BGR2HSV);
Highgui.imwrite("/mnt/sdcard/DCIM/hsvMat4Mask.bmp", hsvMat4Mask);//check
// CREATING A FILTER/MASK FOR RED COLORED BLOB
Mat maskedMat = new Mat();
Core.inRange(hsvMat4Mask, new Scalar(0, 100, 100), new Scalar(10, 255, 255), maskedMat);
Highgui.imwrite("/mnt/sdcard/DCIM/maskedMat.bmp", maskedMat);// check
// COPYING THE MASK TO AN EMPTY MAT
// STEP 1:
List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
Imgproc.findContours(maskedMat, contours, new Mat(), Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_NONE);
//STEP 2:
Mat newMat4Mask = new Mat(rgbaMat4Mask.rows(), rgbaMat4Mask.cols(), CvType.CV_8UC1);
newMat4Mask.setTo(new Scalar(0));
Imgproc.drawContours(newMat4Mask, contours, 0, new Scalar(255), -1);//TODO Using -1 instead of CV_FILLED.
Highgui.imwrite("/mnt/sdcard/DCIM/newMatWithMask.bmp", newMat4Mask);// check
//STEP 3
Log.i(TAG, "HAPPY rows:"+contours.get(0).rows()+" columns:"+contours.get(0).cols());
Mat newMatwithMaskFinished = new Mat(contours.get(0).rows(), contours.get(0).cols(), CvType.CV_8UC3);
newMatwithMaskFinished.setTo(new Scalar(120, 255, 255));
rgbaMat4Mask.copyTo(newMatwithMaskFinished, newMat4Mask);
Highgui.imwrite("/mnt/sdcard/DCIM/newMatwithMaskFinished.bmp", newMatwithMaskFinished);//check*/
}
Your newMatwithMaskFinished should have the same size as rgbaMat4Mask and newMat4Mask.
Mat newMatwithMaskFinished = new Mat(rgbaMat4Mask.rows(), rgbaMat4Mask.cols(), CvType.CV_8UC3);
If you want to have a Mat of the bigger circle only, with transparent background, then you need to:
1) create newMatwithMaskFinished with type CV_8UC4
Mat newMatwithMaskFinished = new Mat(rgbaMat4Mask.rows(), rgbaMat4Mask.cols(), CvType.CV_8UC4);
2) set a transparent background:
newMatwithMaskFinished.setTo(new Scalar(0, 0, 0, 0));
3) Compute the bounding box box of the contour you're interested in, with boundingRect.
4) Convert rgbaMat4Mask to 4 channels (unless it's already), with cvtColor(..., COLOR_BGR2BGRA), let's call this rgba
5) Copy rgba to newMatwithMaskFinished, with mask newMat4Mask.
6) Crop newMatwithMaskFinished on box, using submat method
I'm doing a watershed segmentation and the marker image is derived from the source image put through a distance transform. The distance transform returns a floating point image (I have no idea about the bit-depth) and I have trouble putting it through the watershed method since it requires a 32 bit single channel image.
Can I use the mat's convertTo method to set the bit depth to 32?
I also have trouble trying to display the floating point image since the matToBitmap() method doesn't seem to accept them. (in Android)
Mat mImg = new Mat();
Mat mThresh = new Mat();
Mat mDist = new Mat();
ImageView imgView = (ImageView) findViewById(R.id.imageView);
Bitmap bmpIn = BitmapFactory.decodeResource(getResources(),
R.drawable.w1);
Utils.bitmapToMat(bmpIn, mImg);
Imgproc.cvtColor(mImg, mImg, Imgproc.COLOR_BGR2GRAY);
Imgproc.threshold(mImg, mThresh, 0, 255, Imgproc.THRESH_BINARY
| Imgproc.THRESH_OTSU);
//Marker image for watershed
Imgproc.distanceTransform(mThresh, mDist, Imgproc.CV_DIST_L2, Imgproc.CV_DIST_MASK_PRECISE);
//Conversions for watershed
Imgproc.cvtColor(mThresh, mThresh, Imgproc.COLOR_GRAY2BGR, 3);
//Floating-point image -> 32-bit single-channel
mDist.convertTo(...);
Imgproc.watershed(mThresh, mDist); //
Bitmap bmpOut = Bitmap.createBitmap(mThresh.cols(), mThresh.rows(),
Bitmap.Config.ARGB_8888);
Utils.matToBitmap(mThresh, bmpOut);
imgView.setImageBitmap(bmpOut);
Yes, you can use the convertTo function to convert any opencv matrix to another type. The type to convert to should be set in a destination matrix with the same size. convertTo has optional parameters scale and shift, so you can avoid clipping and quantization errors when converting to fixed point depths. So for your code:
Mat mDist32 = Mat(mDist.rows,mDist.cols,CV_32SC1); // 32 bit signed 1 channel, use CV_32UC1 for unsigned
mDist.convertTo(mDist32,CV_32SC1,1,0);
Imgproc.watershed(mThresh,mDist32);