Develop Reference

Combine Images in Canvas and then view it through ImageView using Android Studio

I want to combine images by putting them on top of eachother in Canvas and then view the combination using ImageView. What I know is if you set the first Bitmap into the Canvas everything else you do will be added to that first Bitmap. I only get the error:
PointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getWidth()' on a null object reference
ImageView mainImage = (ImageView) view.findViewById(R.id.mainImage);
Bitmap bottomImage = BitmapFactory.decodeFile("image1.png");
Bitmap topImage = BitmapFactory.decodeFile("image2.png");
Bitmap tempBitmap = Bitmap.createBitmap(bottomImage.getWidth(), bottomImage.getHeight(), Bitmap.Config.RGB_565);
Canvas tempCanvas = new Canvas(tempBitmap);
tempCanvas.drawBitmap(bottomImage, 0, 0, null);
tempCanvas.drawBitmap(topImage, 0, 0, null);
mainImage.setImageBitmap(bitmap);

Try Below Code
public Bitmap drawImageOnImage(Bitmap background, Bitmap pic, int x_to_draw, int y_to_draw, int width, int height)
{
try
{
Canvas newCanvas = new Canvas(background);
Bitmap img_bitmap = Bitmap.createScaledBitmap(pic, width, height, true);
newCanvas.drawBitmap(img_bitmap, x_to_draw, y_to_draw,new Paint());
}catch (Exception e)
{
System.out.println("Error Occured=>");
e.printStackTrace();
}
return background;
}
Here function takes 2 input bitmaps, Background bitmap and another image bitmap to draw over background bitmap. You will get combined bitmap to set for ImageView. X and Y are the co-rdinates where top image bitmap start paint. Same for height and width

After some experiments this code worked perfectly. And I added multiple top images.
private void drawAndView(ImageView imgView, Bitmap bottomImage, Bitmap[] topImages){
Bitmap tempBitmap = Bitmap.createBitmap(bottomImage.getWidth(), bottomImage.getHeight(), Bitmap.Config.RGB_565);
Canvas tempCanvas = new Canvas(tempBitmap);
tempCanvas.drawBitmap(bottomImage, 0, 0, null);
for (Bitmap bitmap : topImages){
tempCanvas.drawBitmap(bitmap, 0, 0, null);
}
imgView.setImageBitmap(tempBitmap);
}

How do i correctly convert a integer back to Bitmap

In Android Studio I can use the following lines of code to get an array from Bitmap
Bitmap bitmap = get_Image();
Bitmap resizeBitmap = getResizedBitmap(bitmap);
int[] iArr = new int[(resizeBitmap.getWidth() * resizeBitmap.getHeight())];
resizeBitmap.getPixels(iArr, 0, resizeBitmap.getWidth(), 0, 0, resizeBitmap.getWidth(), resizeBitmap.getHeight());
Here is the resizer function:
public Bitmap getResizedBitmap(Bitmap bitmap) {
if (576 == bitmap.getWidth() && 1024 == bitmap.getHeight()) {
return bitmap;
}
Bitmap createBitmap = Bitmap.createBitmap(576, 1024, Config.RGB_565);
Matrix scaledMatrix = scaledMatrix(bitmap.getWidth(), bitmap.getHeight(), createBitmap.getWidth(), createBitmap.getHeight());
new Canvas(createBitmap).drawBitmap(bitmap, scaledMatrix, null);
return createBitmap;
}
However when I convert that int array back to bitmap the image is wrong
Bitmap bmp = Bitmap.createBitmap(1024, 576, Config.RGB_565);
bmp.setPixels(iArr, 0, 1024, 0, 0, 1024, 576);
textViewToChange.setText("Bitmap created");
This is the image when i save it to a file or display it https://imgur.com/a/ZQ0DJAy The above image is how it looks like and below is how it should had looked like
If i read the incorrect image in python, the RGB pixels are placed exactly where they should be like in the correct image but the image dosen't look the same. Why? How can i fix this?

how to modify the height and width of a bitmap

I am working on an Android app, And I put many pictures in Assets directory by categories. And I get a bitmap of a image using code below
InputStream in = getAssets().open(file);
Bitmap bm = BitmapFactory.decodeStream(in);
Bitmap board = Bitmap.createBitmap(bm.getWidth(), bm.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(board);
canvas.drawBitmap(bm,0,0,null);
And the width and height(pixel) of all my image files is 360x240， I want the Bitmap:board to be 960x720 when the images are read because I need convert the bitmap to a 960x720 Mat using OpenCV.
What can I do?

You can use createScaledBitmap :
Bitmap createScaledBitmap (Bitmap src,
int dstWidth,
int dstHeight,
boolean filter)
Creates a new bitmap, scaled from an existing bitmap, when possible.
If the specified width and height are the same as the current width
and height of the source bitmap, the source bitmap is returned and no
new bitmap is created.

Rotation of Image not working

I am using imageView.setRotation(imageView.getRotation+90) on click for rotating image it's working fine. But whenever I sending that image (Rotated Image) to the server it's showing the original view to the server not rotated the view. I'm using Retrofit multipart for sending the image.

imageView.setRotation(imageView.getRotation+90)
it only rotates the imageview not the content of it ,as the result bitmap remians same.
You should rotate the bitmap using
Matrix matrix = new Matrix();
matrix.postRotate(90);
Bitmap scaledBitmap = Bitmap.createScaledBitmap(bitmapOrg,width,height,true);//BitmapOrg- is origanl bitmap
Bitmap rotatedBitmap = Bitmap.createBitmap(scaledBitmap , 0, 0, scaledBitmap .getWidth(), scaledBitmap .getHeight(), matrix, true);
and
imageView.setImageBitmap(rotatedBitmap);
now use the rotatedBitmap to send the server.

capturing image from camera and overlaying another bitmap before we save it

here tempdata is the data captured from camera, savephoto(Bitmap) is a method am using to save the image taken from camera, and it is executing accurately ,,
BUt on [2]
i am overlaying another bitmap ,, and when i am calling the savephoto(p)
it is creating an empty file in the memorycard ...
not saving any image.
how can i overlay the two bitmap on top of each other
[1]File Imgname = Environment.getExternalStorageDirectory();
Bitmap bmp = BitmapFactory.decodeByteArray(tempdata,0,tempdata.length);
imv.setImageBitmap(bmp);
savePhoto(bmp);
[2]Bitmap bmp2 = BitmapFactory.decodeResource(getResources(),R.drawable.ic_launcher);
Bitmap b = Bitmap.createBitmap(bmp.getWidth(), bmp.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(b);
canvas.drawBitmap(bmp, 0,0, null);
canvas.drawBitmap(bmp2, 50, 50, null);
savePhoto(b);
any help will be greatly appreciated
thanx

you can do like this after getting after getting bitmap from camera (assume bitmap1) and your bitmap to overlay on top of bitmap1 (assume bitmap2)
call this overlayMark() with your bitmaps it will return overlay bitmap that is your required bitmap . you can save that bitmap..
private Bitmap overlayMark(Bitmap bmp1, Bitmap bmp2) {
int bh = originalBitmap.getHeight();
int bw = originalBitmap.getWidth();
Bitmap bmOverlay = Bitmap.createBitmap(bw,bh,Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bmOverlay);
canvas.drawBitmap(bmp1, 0, 0, null);
canvas.drawBitmap(bmp2, 0,0, null);
return bmOverlay;
}