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Resize a large bitmap file to scaled output file on Android

Asked 2010-07-26T00:06:25.020
224

I have a large bitmap (say 3888x2592) in a file. Now, I want to resize that bitmap to 800x533 and save it to another file. I normally would scale the bitmap by calling Bitmap.createBitmap method but it needs a source bitmap as the first argument, which I can't provide because loading the original image into a Bitmap object would of course exceed the memory (see here, for example).

I also can't read the bitmap with, for example, BitmapFactory.decodeFile(file, options), providing a BitmapFactory.Options.inSampleSize, because I want to resize it to an exact width and height. Using inSampleSize would resize the bitmap to 972x648 (if I use inSampleSize=4) or to 778x518 (if I use inSampleSize=5, which isn't even a power of 2).

I would also like to avoid reading the image using inSampleSize with, for example, 972x648 in a first step and then resizing it to exactly 800x533 in a second step, because the quality would be poor compared to a direct resizing of the original image.

To sum up my question: Is there a way to read a large image file with 10MP or more and save it to a new image file, resized to a specific new width and height, without getting an OutOfMemory exception?

I also tried BitmapFactory.decodeFile(file, options) and setting the Options.outHeight and Options.outWidth values manually to 800 and 533, but it doesn't work that way.

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3 Answers

151

No. I'd love for someone to correct me, but I accepted the load/resize approach you tried as a compromise.

Here are the steps for anyone browsing:

  1. Calculate the maximum possible inSampleSize that still yields an image larger than your target.
  2. Load the image using BitmapFactory.decodeFile(file, options), passing inSampleSize as an option.
  3. Resize to the desired dimensions using Bitmap.createScaledBitmap().
answered 2010-07-26T00:56:22.343
1

To scale the image the "correct" way, without skipping any pixels, you'd have to hook into the image decoder to perform the down-sampling row by row. Android (and the Skia library that underlies it) provides no such hooks, so you'd have to roll your own. Assuming you're talking jpeg images, your best bet would be to use libjpeg directly, in C.

Given the complexities involved, using the two-step subsample-then-rescale is probably best for image-preview type apps.

answered 2012-08-04T03:01:29.523
0

There is a great article about this exact issue on the Android developer website: Loading Large Bitmaps Efficiently

answered 2013-01-07T11:55:15.783

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