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.
Related
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.
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.
I want to write an android program to compute dct of the input image, and I am using opencv android framework. first of all I convert input image to grayscale and then i want to compute dct using Core.dct() with 16*16 block. this is the dct computation part :
int rownum = 1;
for (int i = 1; i <= M - B + 1; i++) {
for (int j = 1; j <= N - B + 1; j++) {
Mat SubImg = GrayImage.submat(new Range(i, i+B-1), new Range(j, j+B-1));
Mat Block_DCT = Mat.zeros(16, 16, SubImg.type());
Mat Block_DCT_Quantized = Mat.zeros(16, 16, Block_DCT.type());
Core.dct(SubImg, Block_DCT);
Core.divide(Block_DCT, SQ16, Block_DCT_Quantized);
Mat row = Mat.zeros(1, B*B, Block_DCT_Quantized.type());
Block_DCT_Quantized.reshape(1, B*B);
rownum=rownum+1;
}
}
I debug the code and figure out that the application crash on the line Core.dct() !!!
i don't know what is the problem, but I suppose it's because of input type ...
can any body help me ? what should I do ?
Update :
I found the solution, the problem was because of size and type of Mat objects, actually Core.dct() method just work with this type Mat: cv_64fc1. I use SubImg.convertTo() function to change the type and correct the size of block, so it worked...
thanks to Rui Marques for answering...
dct needs float input.
you have to convert your image to CvType.CV_32F or CvType.CV_64F before applying dct / dft
I have a requirement to display somewhat big images on an Android app.
Right now I'm using an ImageView with a source Bitmap.
I understand openGL has a certain device-independent limitation as to
how big the image dimensions can be in order for it to process it.
Is there ANY way to display these images (with fixed width, without cropping) regardless of this limit,
other than splitting the image into multiple ImageView elements?
Thank you.
UPDATE 01 Apr 2013
Still no luck so far all suggestions were to reduce image quality. One suggested it might be possible to bypass this limitation by using the CPU to do the processing instead of using the GPU (though might take more time to process).
I don't understand, is there really no way to display long images with a fixed width without reducing image quality? I bet there is, I'd love it if anyone would at least point me to the right direction.
Thanks everyone.
You can use BitmapRegionDecoder to break apart larger bitmaps (requires API level 10). I've wrote a method that will utilize this class and return a single Drawable that can be placed inside an ImageView:
private static final int MAX_SIZE = 1024;
private Drawable createLargeDrawable(int resId) throws IOException {
InputStream is = getResources().openRawResource(resId);
BitmapRegionDecoder brd = BitmapRegionDecoder.newInstance(is, true);
try {
if (brd.getWidth() <= MAX_SIZE && brd.getHeight() <= MAX_SIZE) {
return new BitmapDrawable(getResources(), is);
}
int rowCount = (int) Math.ceil((float) brd.getHeight() / (float) MAX_SIZE);
int colCount = (int) Math.ceil((float) brd.getWidth() / (float) MAX_SIZE);
BitmapDrawable[] drawables = new BitmapDrawable[rowCount * colCount];
for (int i = 0; i < rowCount; i++) {
int top = MAX_SIZE * i;
int bottom = i == rowCount - 1 ? brd.getHeight() : top + MAX_SIZE;
for (int j = 0; j < colCount; j++) {
int left = MAX_SIZE * j;
int right = j == colCount - 1 ? brd.getWidth() : left + MAX_SIZE;
Bitmap b = brd.decodeRegion(new Rect(left, top, right, bottom), null);
BitmapDrawable bd = new BitmapDrawable(getResources(), b);
bd.setGravity(Gravity.TOP | Gravity.LEFT);
drawables[i * colCount + j] = bd;
}
}
LayerDrawable ld = new LayerDrawable(drawables);
for (int i = 0; i < rowCount; i++) {
for (int j = 0; j < colCount; j++) {
ld.setLayerInset(i * colCount + j, MAX_SIZE * j, MAX_SIZE * i, 0, 0);
}
}
return ld;
}
finally {
brd.recycle();
}
}
The method will check to see if the drawable resource is smaller than MAX_SIZE (1024) in both axes. If it is, it just returns the drawable. If it's not, it will break the image apart and decode chunks of the image and place them in a LayerDrawable.
I chose 1024 because I believe most available phones will support images at least that large. If you want to find the actual texture size limit for a phone, you have to do some funky stuff through OpenGL, and it's not something I wanted to dive into.
I wasn't sure how you were accessing your images, so I assumed they were in your drawable folder. If that's not the case, it should be fairly easy to refactor the method to take in whatever parameter you need.
You can use BitmapFactoryOptions to reduce size of picture.You can use somthing like that :
BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 3; //reduce size 3 times
Have you seen how your maps working? I had made a renderer for maps once. You can use same trick to display your image.
Divide your image into square tiles (e.g. of 128x128 pixels). Create custom imageView supporting rendering from tiles. Your imageView knows which part of bitmap it should show now and displays only required tiles loading them from your sd card. Using such tile map you can display endless images.
It would help if you gave us the dimensions of your bitmap.
Please understand that OpenGL runs against natural mathematical limits.
For instance, there is a very good reason a texture in OpenGL must be 2 to the power of x. This is really the only way the math of any downscaling can be done cleanly without any remainder.
So if you give us the exact dimensions of the smallest bitmap that's giving you trouble, some of us may be able to tell you what kind of actual limit you're running up against.
I'am actually working in a project on android in which I want to extract some specific pixel values (according to a condition, using the threshold method , I have set some pixels to a certain values and all the others to zero) I want to extract all these values different from zero in a vector. I will use this vector of the chosen pixels to do some operation ( the mean value for exemple ) , Is there a method in OpenCV that can help me doing this ?
Thank you :)
I don't know such function but actually it's not hard to implement it (c++):
//'in' should be CV_8UC3
vector<int>& getNonZero(const Mat& in)
{
//get size of result vector
//this is all non-zero pixels:
int count = countNonZero(in);
vector<int>& result(count);
int k = 0;
for (int r = 0; r < in.rows; ++r)
{
for (int c = 0; c < in.cols; ++c)
{
if (in.at<int>(r, c))
{
result[k++] = in.at<int>(r, c);
}
}
}
return result;
}
And also many OpenCV functions have InputArray mask parameter so use it! For example:
void meanStdDev(InputArray src, OutputArray mean, OutputArray stddev, InputArray mask=noArray())