Crop image without loading into memory

Question

I want to crop image of large size and tried using Bitmap.createBitmap but it gives OOM error. Also, tried multiple technique around createBitmap but none of them were succe

Answer 1

I very much doubt you can solve this problem with the existing Android API.

What you need to do is obtain one of the available image access libraries (libpng is probably your best bet) and link it to your application via jni (see if there's a Java binding already available).

Use the low-level I/O operations to read the image a single scanline at a time. Discard any scanlines before or after the vertical cropped region. For those scanlines inside the vertical cropped region, take only those pixels inside the horizontal cropped region and write them out to the cropped image.

Answer 2

There is a class called BitmapRegionDecoder which might help you, but it's available from API 10 and above.

If you can't use it :

Many image formats are compressed and therefore require some sort of loading into memory.

You will need to read about the best image format that fits your needs, and then read it by yourself, using only the memory that you need.

a little easier task would be to do it all in JNI, so that even though you will use a lot of memory, at least your app won't get into OOM so soon since it won't be constrained to the max heap size that is imposed on normal apps.

Of course, since android is open source, you can try to use the BitmapRegionDecoder and use it for any device.