How to create the bitmap and decode it at the same time

Question

I am creating a bitmap and it takes about 11 mb in the heap , though it is of the small size. Well I wanted to know if I can create the bitmap and also sclae it as a same time. The reason I want to do it is , the memory allocation , as If I understand correctly from different bitmap questions which are posted here , and that is

The bitmap allocates the memory as when it is created

So if its , then scaling it again take some process time and also increase the heap size until and unless the garbage collection is not occurred

So what I am doing is

        screenHeight = displaymetrics.heightPixels;
        screenWidth = displaymetrics.widthPixels;
        float aspectRatio = screenWidth / screenHeight;

        int modifiedScreenHeight = 400;
        int modifiedScreenWidth = (int) (modifiedScreenHeight * aspectRatio);
        mBitmap = Bitmap.createBitmap(modifiedScreenWidth, modifiedScreenHeight, Bitmap.Config.ARGB_8888);

So now it is creating the bitmap and allocation the memory , by memory analyzer tool in android studio I can see that it took 11mb in memory.

But I want to minimize them ,I have visited a link and I want to do some more scaling by options as show in this video . but it uses the file to decode such as

BitmapFactory.decodeFile(??,options);

where as I have no file to decode from , I want to decode it from the bitmap I created and to wash away the last created bitmap to clear the memory.

Or if it is possible to set the options when creating it so that we can avoid from extra memory allocation .

Please help.

I don't fully understand your question. You are creating a bitmap with Bitmap.createBitmap(), and *fixing its width and height*. Then why would you want to scale it down later? Just create it directly with less width and less height. — natario, Nov 02 '15 at 09:58
@mvai though your question cleared 50 percent of mine views about bitmap , but how can I set the options in the creation ? like I can set the width and height of the bitmap while creating but how to set the options with configration — Coas Mckey, Nov 02 '15 at 10:12
There are no more options for a bitmap created like that - width, height and color config. Depending on what you want to do with that bitmap, you can use a color config which uses less resources (e.g. try RGB_565 and you will have less memory allocation, but also less quality) — natario, Nov 02 '15 at 10:16

score 1 · Answer 1 · answered Nov 02 '15 at 09:50

You can use this using BitmapFactory.Options - specifically, use the options to decode the width / height of the bitmap, then sampleSize to determine how large the generated bitmap will be.

According to your example, you'd like the width/height of the bitmap to be 400 by 400 * aspectRatio. So, first, you'll need to see how large the bitmap needs to be. Do this as so:

BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;

BitmapFactory.decodeFile(??, options);

int bitmapWidth = options.outWidth;
int bitmapHeight = options.outHeight;

This action will only decode the bitmaps size, without actually allocating memory for the bitmap's pixels. This is good because it's a very quick and light operation which doesn't require much resources and helps you make a more educated decision when loading the bitmap. Now we must use these size to determine how big the generated bitmap will be.

int sampleSize = 1;

while (bitmapWidth / sampleSize > 400 && bitmapHieght / sampleSize > 400 * aspectRatio)
    sampleSize *= 2;

sampleSize must be a power of 2 for this to work, and what it will do is determine how many pixels to "skip" when reading the bitmap into memory. This algorithm will set a sample size to a size equal to 1st sample size which will produce a bitmap immediately smaller than the required bounds. You can tweak this if you'd like a slightly different implementation.

Now that you have the sample size, set it with in the options object and load the actual bitmap:

options.inJustDecodeBounds = false;
options.inSampleSize = sampleSize;

Bitmap bitmap = BitmapFactory.decodeFile(??, options);

The generated bitmap will be smaller than the required bounds, thus limiting your memory requirements for creating the bitmap object.

Hope this helps.

While true, this does not fully answers the OP - he is asking about limiting memory allocation for a `Bitmap` object, which he can't create via `BitmapFactory`. — natario, Nov 02 '15 at 09:56
yeah @mvai is right , and also , how to do the Bitmap bitmap = BitmapFactory.decodeFile(??, options); while I have no file to put here in — Coas Mckey, Nov 02 '15 at 10:15

How to create the bitmap and decode it at the same time

1 Answers1