Develop Reference

Opencv Android : how to remove black background from thresholding output?

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

Converting Bitmap To Mat through Utils.bitmapToMat changes its color [duplicate]

So I make a bitmap from a blob with the next code:
byte[] blob = contact.getMP();
ByteArrayInputStream inputStream = new ByteArrayInputStream(blob);
Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
Bitmap scalen = Bitmap.createScaledBitmap(bitmap, 320, 240, false);
and it gives back the next output, which is good
Then I do the following to make the bitmap into a Mat, but then my colors just change...
//Mat ImageMat = new Mat();
Mat ImageMat = new Mat(320, 240, CvType.CV_32F);
Utils.bitmapToMat(scalen, ImageMat);
I have no idea why, nor another way to make the bitmap into a Mat. What is wrong?

The format of color channels in Android Bitmap are RGB
But in opencv Mat, the channels are BGR by default.
So when you do Utils.bitmapToMat(), [B,G,R] values are stored in [R,G,B] channels. The red and blue channels are interchanged.
One possible solution is to apply cvtcolor on the opencv Mat you got as below:
Imgproc.cvtColor(ImageMat, ImageMat, Imgproc.COLOR_BGR2RGB);
It worked for me.

Color Banding Android Solution

What is possible solution to banded images in Android Activity or in OpenGl.
Look at the answer below.
Hope it Helps

Color Banding Solved ooooooooooyyyyyyyeaaaaaaaaaa
I solved color banding in two phases
1) * when we use the BitmapFactory to decode resources it decodes the resource in RGB565 which shows color banding, instead of using ARGB_8888, so i used BitmapFactory.Options for setting the decode options to ARGB_8888
second problem was whenever i scaled the bitmap it again got banded
2) This was the tough part and took a lot of searching and finally worked
* the method Bitmap.createScaledBitmap for scaling bitmaps also reduced the images to RGB565 format after scaling i got banded images(the old method for solving this was using at least one transparent pixel in a png but no other format like jpg or bmp worked)so here i created a method CreateScaledBitmap to scale the bitmap with the original bitmaps configurations in the resulting scale bitmap(actually i copied the method from a post by logicnet.dk and translated in java)
BitmapFactory.Options myOptions = new BitmapFactory.Options();
myOptions.inDither = true;
myOptions.inScaled = false;
myOptions.inPreferredConfig = Bitmap.Config.ARGB_8888;//important
//myOptions.inDither = false;
myOptions.inPurgeable = true;
Bitmap tempImage =
BitmapFactory.decodeResource(getResources(),R.drawable.defaultart, myOptions);//important
//this is important part new scale method created by someone else
tempImage = CreateScaledBitmap(tempImage,300,300,false);
ImageView v = (ImageView)findViewById(R.id.imageView1);
v.setImageBitmap(tempImage);
// the function
public static Bitmap CreateScaledBitmap(Bitmap src, int dstWidth, int dstHeight, boolean filter)
{
Matrix m = new Matrix();
m.setScale(dstWidth / (float)src.getWidth(), dstHeight / (float)src.getHeight());
Bitmap result = Bitmap.createBitmap(dstWidth, dstHeight, src.getConfig());
Canvas canvas = new Canvas(result);
//using (var canvas = new Canvas(result))
{
Paint paint = new Paint();
paint.setFilterBitmap(filter);
canvas.drawBitmap(src, m, paint);
}
return result;
}
Please correct me if i am wrong.
Also comment if it worked for you.
I am so happy i solved it, Hope it works for you All.
For OpenGl you simply bind the bitmap created after applying upper functions

greyscale Iplimage to android bitmap

I am using opencv to convert android bitmap to grescale by using opencv. below is the code i am using,
IplImage image = IplImage.create( bm.getWidth(), bm.getHeight(), IPL_DEPTH_8U, 4); //creates default image
bm.copyPixelsToBuffer(image.getByteBuffer());
int w=image.width();
int h=image.height();
IplImage grey=cvCreateImage(cvSize(w,h),image.depth(),1);
cvCvtColor(image,grey,CV_RGB2GRAY);
bm is source image. This code works fine and converts to greyscale, i have tested it by saving to sdcard and then loading again, but when i try to load it using below method my app crashes, any suggestions.
bm.copyPixelsFromBuffer(grey.getByteBuffer());
iv1.setImageBitmap(bm);
iv1 is imageview where i want to set the bm.

I've never used the OpenCV bindings for Android, but here's some code to get you started. Regard it as pseudocode, because I can't try it out... but you'll get the basic idea. It may not be the fastest solution. I'm pasting from this answer.
public static Bitmap IplImageToBitmap(IplImage src) {
int width = src.width;
int height = src.height;
Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
for(int r=0;r<height;r++) {
for(int c=0;c<width;c++) {
int gray = (int) Math.floor(cvGet2D(src,r,c).getVal(0));
bitmap.setPixel(c, r, Color.argb(255, gray, gray, gray));
}
}
return bitmap;
}

Your IplImage grey has only one channel, and your Bitmap bm has 4 or 3 (ARGB_8888, ARGB_4444, RGB_565). Therefore the bm can't store the greyscale image. You have to convert it to rgba before use.
Example:
(your code)
IplImage image = IplImage.create( bm.getWidth(), bm.getHeight(), IPL_DEPTH_8U, 4);
bm.copyPixelsToBuffer(image.getByteBuffer());
int w=image.width(); int h=image.height();
IplImage grey=cvCreateImage(cvSize(w,h),image.depth(),1);
cvCvtColor(image,grey,CV_RGB2GRAY);
If you want to load it:
(You can reuse your image or create another one (temp))
IplImage temp = cvCreateImage(cvSize(w,h), IPL_DEPTH_8U, 4); // 4 channel
cvCvtColor(grey, temp , CV_GRAY2RGBA); //color conversion
bm.copyPixelsFromBuffer(temp.getByteBuffer()); //now should work
iv1.setImageBitmap(bm);
I might it will help!

How to get a Bitmap from a raw image

I am reading a raw image from the network. This image has been read by an image sensor, not from a file.
These are the things I know about the image:
~ Height & Width
~ Total size (in bytes)
~ 8-bit grayscale
~ 1 byte/pixel
I'm trying to convert this image to a bitmap to display in an imageview.
Here's what I tried:
BitmapFactory.Options opt = new BitmapFactory.Options();
opt.outHeight = shortHeight; //360
opt.outWidth = shortWidth;//248
imageBitmap = BitmapFactory.decodeByteArray(imageArray, 0, imageSize, opt);
decodeByteArray returns null, since it cannot decode my image.
I also tried reading it directly from the input stream, without converting it to a Byte Array first:
imageBitmap = BitmapFactory.decodeStream(imageInputStream, null, opt);
This returns null as well.
I've searched on this & other forums, but cannot find a way to achieve this.
Any ideas?
EDIT: I should add that the first thing I did was to check if the stream actually contains the raw image. I did this using other applications `(iPhone/Windows MFC) & they are able to read it and display the image correctly. I just need to figure out a way to do this in Java/Android.

Android does not support grayscale bitmaps. So first thing, you have to extend every byte to a 32-bit ARGB int. Alpha is 0xff, and R, G and B bytes are copies of the source image's byte pixel value. Then create the bitmap on top of that array.
Also (see comments), it seems that the device thinks that 0 is white, 1 is black - we have to invert the source bits.
So, let's assume that the source image is in the byte array called Src. Here's the code:
byte [] src; //Comes from somewhere...
byte [] bits = new byte[src.length*4]; //That's where the RGBA array goes.
int i;
for(i=0;i<src.length;i++)
{
bits[i*4] =
bits[i*4+1] =
bits[i*4+2] = ~src[i]; //Invert the source bits
bits[i*4+3] = 0xff; // the alpha.
}
//Now put these nice RGBA pixels into a Bitmap object
Bitmap bm = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
bm.copyPixelsFromBuffer(ByteBuffer.wrap(bits));

Once I did something like this to decode the byte stream obtained from camera preview callback:
Bitmap.createBitmap(imageBytes, previewWidth,　previewHeight,
Bitmap.Config.ARGB_8888);
Give it a try.

for(i=0;i<src.length;i++)
{
bits[i*4] = bits[i*4+1] = bits[i*4+2] = ~src[i]; //Invert the source bits
bits[i*4+3] = 0xff; // the alpha.
}
The conversion loop can take a lot of time to convert the 8 bit image to RGBA, a 640x800 image can take more than 500ms... A quicker solution is to use ALPHA8 format for the bitmap and use a color filter:
//setup color filter to inverse alpha, in my case it was needed
float[] mx = new float[]{
1.0f, 0, 0, 0, 0, //red
0, 1.0f, 0, 0, 0, //green
0, 0, 1.0f, 0, 0, //blue
0, 0, 0, -1.0f, 255 //alpha
};
ColorMatrixColorFilter cf = new ColorMatrixColorFilter(mx);
imageView.setColorFilter(cf);
// after set only the alpha channel of the image, it should be a lot faster without the conversion step
Bitmap bm = Bitmap.createBitmap(width, height, Bitmap.Config.ALPHA_8);
bm.copyPixelsFromBuffer(ByteBuffer.wrap(src)); //src is not modified, it's just an 8bit grayscale array
imageview.setImageBitmap(bm);

Use Drawable create from stream. Here's how to do it with an HttpResponse, but you can get the inputstream anyway you want.
InputStream stream = response.getEntity().getContent();
Drawable drawable = Drawable.createFromStream(stream, "Get Full Image Task");