Develop Reference

Android YUV to grayscale performance optimization

I'm trying to convert an YUV image to grayscale, so basically I just need the Y values.
To do so I wrote this little piece of code (with frame being the YUV image):
imageConversionTime = System.currentTimeMillis();
size = frame.getSize();
byte nv21ByteArray[] = frame.getImage();
int lol;
for (int i = 0; i < size.width; i++) {
for (int j = 0; j < size.height; j++) {
lol = size.width*j + i;
yMatrix.put(j, i, nv21ByteArray[lol]);
}
}
bitmap = Bitmap.createBitmap(size.width, size.height, Bitmap.Config.ARGB_8888);
Utils.matToBitmap(yMatrix, bitmap);
imageConversionTime = System.currentTimeMillis() - imageConversionTime;
However, this takes about 13500 ms. I need it to be A LOT faster (on my computer it takes 8.5 ms in python) (I work on a Motorola Moto E 4G 2nd generation, not super powerful but it should be enough for converting images right?).
Any suggestions?
Thanks in advance.

First of all I would assign size.width and size.height to a variable. I don't think the compiler will optimize this by default, but I am not sure about this.
Furthermore Create a byte[] representing the result instead of using a Matrix.
Then you could do something like this:
int[] grayScalePixels = new int[size.width * size.height];
int cntPixels = 0;
In your inner loop set
grayScalePixels[cntPixels] = nv21ByteArray[lol];
cntPixels++;
To get your final image do the following:
Bitmap grayScaleBitmap = Bitmap.createBitmap(grayScalePixels, size.width, size.height, Bitmap.Config.ARGB_8888);
Hope it works properly (I have not tested it, however at least the shown principle should be applicable -> relying on a byte[] instead of Matrix)

Probably 2 years too late but anyways ;)
To convert to gray scale, all you need to do is set the u/v values to 128 and leave the y values as is. Note that this code is for YUY2 format. You can refer to this document for other formats.
private void convertToBW(byte[] ptrIn, String filePath) {
// change all u and v values to 127 (cause 128 will cause byte overflow)
byte[] ptrOut = Arrays.copyOf(ptrIn, ptrIn.length);
for (int i = 0, ptrInLength = ptrOut.length; i < ptrInLength; i++) {
if (i % 2 != 0) {
ptrOut[i] = (byte) 127;
}
}
convertToJpeg(ptrOut, filePath);
}
For NV21/NV12, I think the loop would change to:
for (int i = ptrOut.length/2, ptrInLength = ptrOut.length; i < ptrInLength; i++) {}
Note: (didn't try this myself)
Also I would suggest to profile your utils method and createBitmap functions separately.

Detect Values of RGB from CameraFrame using OpenCV in Android

I want to detect which value is maximum from RGB. how can I detect that?
I want to display which colour has highest occurrence with their
RGB value. For example, In a image the RED colour has highest occurrence so it will display colour as RED and with their value in percentage.
I have tried it by getting rows and cols of image like below:
public Mat onCameraFrame(CvCameraViewFrame cvf) {
mRgba = cvf.rgba();
int rows = mRgba.rows();
int cols = mRgba.cols();
// int ch = mRgba.channels();
double R=0,G=0,B=0;
for (int i=0; i<rows; i++)
{
for (int j=0; j<cols; j++)
{
double[] data = mRgba.get(i, j); //Stores element in an array
R = data[0];
G= data[1];
B = data[2];
}
}
Imgproc.putText(mRgba,"R:"+R + "G:"+G +"B:"+B,new Point(10,52),Core.FONT_HERSHEY_COMPLEX,.7,new Scalar(5,255,255), 2,8,false );
return mRgba;
}
but it is taking to much time and screen is lagging because I have implemented code in onCameraFrame. So how can I detect it fast in this method and which is the best way to it?
Thanks.

For such tasks you should use AsyncTask as it does not run on MainThread thus your UI wont freeze.
https://developer.android.com/reference/android/os/AsyncTask.html
I assume that this will be faster compared to your current solution.

Split the image into its R, G and B channels, and compute the sum of each Mat.
vector<Mat> channels;
split(mRgba, channels);
B = sum(channels[0])[0];
G = sum(channels[1])[0];
R = sum(channels[2])[0];
Compare the values of R, G and B to know which colour has occurred the most in the frame.

Having problems using setPixel() method

Can someone explain me the way setPixel() method works in Android? I am trying to replace some pixels on a bitmap. I extract them by using getPixel() method and their individual colors, eg.green = Color.green(a[i][j]);, but I cannot set them new values back, so as to show the processed image onscreen.
Edit: This is where some of the processing occurs. I try to algorithmically convert to grayscale
for (int i = 0; i < grayWidth; i++) {
for (int j = 0; j < grayHeight; j++) {
a[i][j] = myImage.getPixel(i, j);
red = Color.red(a[i][j]);
green = Color.green(a[i][j]);
blue = Color.blue(a[i][j]);
gray = (red + green + blue) / 3;
a[i][j] = gray;
}
}
and then replace pixels:
for (int m = 0; m < grayHeight; m++) {
for (int n = 0; n < grayWidth; n++) {
grayScale.setPixel(m, n, a[m][n]);
}
}
and finally show it on-screen
imageView.setImageBitmap(grayScale);
Sorry for not explaining it thoroughly in the first place/

Why posts questions without any code? Put yourself in our position, how can we help you, if we do not know what you are trying to do? You're only presenting your problem in English language, which does not equal to programming language in most cases. We want to see the latter, supported with english description of what you are doing and what's going on.
Based on provided information and Android Dev Page for Bitmap, I can assume that your BitMap image might not be mutable. This would throw then IllegalStateException, but without seeing your LogCat / Code, I cannot be sure, whether this is the case.
If the BitMap indeed is immutable, then you can try and look at converting immutable bitmap to mutable and try again.

how to get pixel color using byte array in Android

In my Android project,
Here is my code.
for (int x = 0; x < targetBitArray.length; x += weight) {
for (int y = 0; y < targetBitArray[x].length; y += weight) {
targetBitArray[x][y] = bmp.getPixel(x, y) == mSearchColor;
}
}
but this code wastes a lot of time.
So I need to find way faster than bitmap.getPixel().
I'm trying to get pixel color using byte array converted from bitmap, but I can't.
How to replace Bitmap.getPixel()?

Each Bitmap.getPixel method invocation requires a lot of resources, so you need to avoid the amount of requests in order to improve the performace of your code.
My suggestion is:
Read the image data row-by-row with Bitmap.getPixels method into a local array
Iterate along your local array
e.g.
int [] rowData= new int [bitmapWidth];
for (int row = 0; row < bitmapHeight; row ++) {
// Load row of pixels
bitmap.getPixels(rowData, 0, bitmapWidth, 0, row, bitmapWidth, 1);
for (int column = 0; column < bitmapWidth; column ++) {
targetBitArray[column][row] = rowData(column) == mSearchColor;
}
}
This will be a great improvement for the performace of your code

Image Processing in an Android Application using RGB

I'll be creating an Android Application that determines the freshness of meat using it's RGB. The flow of the application would be:
Capture an image
Determine the freshness by clicking one button
Displaying the result based from it's RGB.
I have a problem in the RGB part. Hope somebody can help me with this matter.

If you are using Processing this could be useful.
Use Processing to scan an image pixel by pixel, so they could be compare to find pattern's in the image.
PImage sample;
void setup() {
size(300,300);
sample = loadImage("sample.jpg");
sample.loadPixels();
image(sample,0,0,300,300);
}
void draw() {
//Loop to scan the image pixel by pixel
for (int x=0; x < sample.width; x++){
for (int y=0; y < sample.height; y++){
int location = x + (y * sample.width);
// Whit the location you can get the current color
color currentColor = sample.pixels[loc];
//Do something
}
}
}