Develop Reference

Bitmap compress grainy image after saving

I'm performing a transformation on an image via Glide transformation, setting it as a background to a view with a black background, then saving it the device as a PNG. The view looks like this:
After compressing it and saving it as a PNG, it looks like this:
Ignoring the size and background difference, notice the graininess around the edges. This is persisted after the save. The PNG is the correct size as the original image so no scaling was performed. How do I prevent this from happening? The code to compress is:
File file = new File(context.getFilesDir().getPath() + "/" + String.valueOf(num) + ".png");
OutputStream os = null;
try {
os = new FileOutputStream(file);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
bitmap.compress(Bitmap.CompressFormat.PNG, 100, os);
Properties set to the bitmap were:
Bitmap b = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
b.setHasAlpha(true);
Things I've tried:
Using WEBP; same issue.
Saving the view and building a drawing cache,
then saving that bitmap. Again, same issue.
Can't use JPEG since I need the alpha layer.
It seems like the compression to PNG can't handle bright colors.
Update:
Using RGB_565 instead of ARGB_8888 removes the graininess but adds black to the outside, since there's no alpha layer. Seems like the compression can't handle it if there are any alpha pixels.

Try using BitmapFactory.decodeFile
String filePath = context.getFilesDir().getPath() + "/" + String.valueOf(num) + ".png";
BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Bitmap.Config.ARGB_8888;
options.inDither = false;
BitmapFactory.decodeFile(filePath, options);
Alternatively, you can use createScaledBitmap method, it has a flag where you can set if the scaled image should be filtered or not. That flag improves the quality of the bitmap.
boolean shouldFilter = false;
bitmap.createScaledBitmap(bitmap, desiredWidth, desiredHeight, shouldFilter);

Saving View bitmap with getDrawingCache gives a black image

Everything I tried with setDrawingCacheEnabled and getDrawingCache was not working. The system was making an image but it just looked black.
Other people on SO seemed to be having a similar problem but the answers seemed either too complicated or irrelevant to my situation. Here are some of the ones I looked at:
Save view like bitmap, I only get black screen
Screenshot shows black
getDrawingCache always returns the same Bitmap
Convert view to bitmap on Android
bitmap is not saving properly only black image
Custom view converting to bitmap returning black image
And here is my code:
view.setDrawingCacheEnabled(true);
Bitmap bitmap = view.getDrawingCache();
try {
FileOutputStream stream = new FileOutputStream(getApplicationContext().getCacheDir() + "/image.jpg");
bitmap.compress(CompressFormat.JPEG, 80, stream);
stream.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
view.setDrawingCacheEnabled(false);
I'm sharing my answer below in case anyone else makes the same mistake I did.

My problem was that my view was a TextView. The text on the TextView was black (naturally) and in the app the background looked white. However, I later recalled reading that a view's background is by default transparent so that whatever color is below shows through.
So I added android:background="#color/white" to the layout xml for the view and it worked. When I had been viewing the image before I had been looking at black text over a black background.
See the answer by #BraisGabin for an alternate way that does not require overdrawing the UI.

I just found a good option:
final boolean cachePreviousState = view.isDrawingCacheEnabled();
final int backgroundPreviousColor = view.getDrawingCacheBackgroundColor();
view.setDrawingCacheEnabled(true);
view.setDrawingCacheBackgroundColor(0xfffafafa);
final Bitmap bitmap = view.getDrawingCache();
view.setDrawingCacheBackgroundColor(backgroundPreviousColor);
bitmap.compress(Bitmap.CompressFormat.JPEG, 80, stream);
view.setDrawingCacheEnabled(cachePreviousState);
Where 0xfffafafa is the desired background color.

Used below code to get bitmap image for view it work fine.
public Bitmap loadBitmapFromView(View v) {
DisplayMetrics dm = getResources().getDisplayMetrics();
v.measure(View.MeasureSpec.makeMeasureSpec(dm.widthPixels,
View.MeasureSpec.EXACTLY),
View.MeasureSpec.makeMeasureSpec(dm.heightPixels,
View.MeasureSpec.EXACTLY));
v.layout(0, 0, v.getMeasuredWidth(), v.getMeasuredHeight());
Bitmap returnedBitmap =
Bitmap.createBitmap(v.getMeasuredWidth(),
v.getMeasuredHeight(), Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(returnedBitmap);
v.draw(c);
return returnedBitmap;
}

Android draw area from Bitmap or Imageview with canvas

i'm trying to draw a Bitmap but only with a selected area from the original Bitmap or Imageview. The requirement is that the final picture must show only 1/3 from the top of the original Bitmap. I attach a draft. I suppose that i should use canvas, but i do not know exactly how it works.
Thanks in advance!!

Bitmap getTheReducedBitmap(Bitmap fullLengthBitnap)
{
Bitmap backDrop=Bitmap.createBitmap(fullLengthBitnap.getWidth(), fullLengthBitnap.getHeight()/3, Bitmap.Config.RGB_565);
Canvas can = new Canvas(backDrop);
can.drawBitmap(fullLengthBitnap, 0, 0, null);
return backDrop;
}

This is the documentation for the method you should use.
private void draw(Canvas c, Bitmap bmp){
Rect r=new Rect(0,0,bmp.width,bmp.height/3);
Rect drawR=new Rect(0,0,c.width,c.height/3);
c.drawBitmap(bmp,r,drawR,null);
}
or as a one liner:
c.drawBitmap(bmp,new Rect(0,0,bmp.width,bmp.height/3),new Rect(0,0,c.width,c.height/3),null);
It allows you to specify where on the canvas you want to draw it too, and where you want the segment to be from.
#Eu.Dr. 's answer would not work if you wanted to draw anything else on the canvas below it.

val newBitmap=Bimtap
.createBitmap(your_view.width,your_view.height,Bitmap.Config.ALPHA_8)
//note: for tablet mode your_view.width,height will increase drastically so
//you might want
//to fix the size of drawing area for optimization
//ALPHA_8 each pixel requires 1 byte of memory.
//RGB_565 Each pixel is stored on 2 bytes
//ARGB_8888 Each pixel is stored on 4 bytes
//after this you can further apply the compress like
[Refer more from google][1]
val stream = ByteArrayOutputStream();
newBitmap.compress(Bitmap.CompressFormat.PNG, 80, stream);
val byteArray = stream.toByteArray(); // convert drawing photo to byte array
// save it in your internal storage.
val storageDir = getExternalFilesDir(Environment.DIRECTORY_PICTURES
+"attendance_sheet.png");
try{
val fo = FileOutputStream(storageDir);
fo.write(byteArray);
fo.flush();
fo.close();
}catch(Exception ex){
}

Bitmap color change while compressing to png

I'm currently working on a steganogrpahy android app as a class project. I've created an object that will encode an image with in another image and return an encoded bitmap. This code is run in a seprate thread.
new Thread(new Runnable()
{
public void run()
{
Bitmap encoded_image = null;
Encryptor encryptor = new Encryptor();
encoded_image = encryptor.encode_image_in_image(
image_location,message_image_location);
}
}).start();
After encoding the bitmap I was passing the bitmap to a file browser activity that I've created to save the bitmap as a png image. This method works for smaller images however, when a large image is encoded and passed to the sub activity the application freezes and returns to the main activity.
private void pass_image_to_file_browser( Bitmap image )
{
Intent intent = new Intent(Encrypt.this,FileBrowser.class);
intent.putExtra( Intent.EXTRA_STREAM, image );
startActivity( intent );
}
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
Bundle bundle = this.getIntent().getExtras();
Bitmap image = bundle.getParacable(Intent.EXTRA_STREAM);
}
I was assuming a large bitmap was to large to send between activities using an intent so I decided to simply save the image in a temporary location and pass the image's location to the sub activity. Which then saves the png image where the user specifies and deletes the temporary image file.
private void save_bitmap( Bitmap image, String location )
{
FileOutputStream fileOutputStream = new FileOutputStream(location);
BufferedOutputStream buffered_output_stream = new
BufferOutputStream(fileOutputStream);
image.compress(CompressFormat.PNG, 0, buffered_output_stream);
buffered_output_stream.flush();
buffered_output_stream.close();
}
This solves the problem of sending a large bitmap from one activity to another however, has created a new problem that I haven't been able to solve. Both the temporary image that is saved before passing the file location to the sub activity and the image file after re saving the image using the file browser have both had their color changed slightly. This color change is unrecognizable to the naked eye but, when decoding the image it causes lots of problems.
One thought I had was that the Bitmap.Config was changing from ARGB_8888 to ARGB_4444 or RGB_565 however, after debug this is not the case. The bitmap is instantiated as an ARGB_8888 and saved as an ARGB_8888 bitmap and never changes in between. The code still works if I pass the entire bitmap to the file browser activity and I'm saving the bitmaps exactly the same in both places. I do not have any thoughts on what else could be causing this. I'm looking for suggestions on what else could be causing the problem. Sorry I was going to post images on the output in both cases however, stack overflow wouldn't let me at my reputation level Thanks.

Ok, after many long wasted hours worrying about the thread and the algorithm I was using to encode the the bitmap the problem was a little simpler. While decoding the image file that was to be encoded with a message I was using options.inPreferredConfig = Config.ARGB_8888; During debugging I was checking to make sure this didn't change to RGB_565. Although the bitmap object was loaded as ARBG_8888 the image file did not contain an alpha channel and thus even though the bitmap had a byte for the alpha level and would allow me to edit the alpha byte of a pixel through Bitmap.setPixel( x, y, color) the bitmap object never recognized that it had alpha values set. When compressing the bitmap compressed to RGB_565 since the object thought that there was no alpha channel. Somehow this problem was resolved by passing the bitmap to a sub activity and parsing it. I'm guessing when object was being recreated the alpha values I had set were recognized. To solve the problem with out passing the bitmap to a subactivity one must add an alpha channel after decoding a bitmap from a file. I found a function to do so here.
private Bitmap adjustOpacity( Bitmap bitmap )
{
int width = bitmap.getWidth();
int height = bitmap.getHeight();
Bitmap dest = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
int[] pixels = new int[width * height];
bitmap.getPixels(pixels, 0, width, 0, 0, width, height);
dest.setPixels(pixels, 0, width, 0, 0, width, height);
return dest;
}
I'm not sure if there is a more efficient method

For anyone who stumbles upon it, like me, wondering why bitnap colors change once you write it out in PNG. I have found out that using bitmap.setPreMultiplied(false) before calling bitmap.compress(PNG, 100, fileout) preserves the color of your image if it has alpha channel values. Setpremultiplied prevents the pixels written onto disk from being multiplied by alpha channel, thus generating different pixel color values.

Print Bitmaps onto other bitmap android

I am trying to make my game a bit easier on the phone, so I am trying to figure out a way to print a bunch of bitmaps onto another big one, so I can just do it once, rather than every time the screen is redrawn. So, is there any way to do this? I know there is a way to print everything that is printed to the canvas to a bitmap, but I can't seem to get that to work. If that is the only way can someone explain how to do that? Thanks in advance.
Here is something I tried, but it didn't work out so well
Bitmap background;
Canvas canvas;
private void methodName() {
background = Bitmap.createBitmap(width, height, someKindOfConfigThing);
canvas = new Canvas(background);
canvas.drawBitmap(blahblah);
}

What you would do is to create the main bitmap, attach that to a canvas to which you can draw.
Bitmap bitmap = Bitmap.createBitmap(width, height, Config.RGB_565);
Canvas c = new Canvas(bitmap);
You can draw (parts of) bitmaps to this canvas using
c.drawBitmap(anotherBitmap, transformMatrix, paint);
To attach the main bitmap to the view you would create a new ImageView, call setImageBitmap passing your main bitmap and set it as the current contentview using setContentView.

If you want to combine multiple bitmaps to another big one and reuse that, you already on the right way! Show us what you have done and tell us what the result is. I guess we can help you :)
[update] it should be possible to save this new bitmap to disc or store it temporarily as a variable:
private void methodName() {
background = Bitmap.createBitmap(width, height, someKindOfConfigThing);
canvas = new Canvas(background);
// drawing on the canvas should change the bitmap "background" too
canvas.drawBitmap(blahblah);
FileOutputStream fos = null;
try {
fos = new FileOutputStream("/path/to/image.png");
background.compress(Bitmap.CompressFormat.PNG, 100, fos);
fos.close();
} catch (Exception e) {
// catching...
}
}