Android: Bitmap resizing using better resampling algorithm than bilinear (like Lanczos3)

Question

Is there any way or external library that can resize image using Lanczos (ideally) or at least bicubic alg. under Android? (faster is better of course, but quality is priority, a processing time is secondary)

Everything what I've got so far is this:

Bitmap resized = Bitmap.createScaledBitmap(yourBitmap, newWidth, newHeight, true);

However it uses bilinear filter and the output quality is terrible. Especially if you want to preserve details (like thin lines or readable texts).

There are many good libraries for Java as discussed for example here: Java - resize image without losing quality

However it's always depended on Java awt classes like java.awt.image.BufferedImage, so it can't be used in Android.

Is there a way how to change the default (bilinear) filter in Bitmap.createScaledBitmap() method or some library like Morten Nobel's lib that is able to work with android.graphics.Bitmap class (or with some raw representation, as @Tron in the comment has pointed out)?

Answer 1

Unfortunately Android uses android.graphics.Bitmap which does not exist in java while java uses java.awt.image.BufferedImage that does not exist in android :-(

I donot have a ready to use library for android but a path how to port a java-awt specific lib to a platform independat java lib with platfrom specific handlers for android and awt/j2se

In the java rescale lib you have to hide all java-awt specific classes (like BufferedImage) behind an interface IBitmap and implement that interface for j2se and independantly for Android.

I have done this successfully for exif/icc/ipc metadata processing and implemented interface pixymeta-lib/.../IBitmap.java with implementation for j2se pixymeta-j2se-lib/.../j2se/BitmapNative.java and android pixymeta-android-lib/.../android/BitmapNative.java

So I have these packages

• pixymeta-lib
  • transformed platform independant lib where all awt-references are replaced by IBitmap interface
• pixymeta-j2se-lib
  • awt/j2se implementation of IBitmap
• pixymeta-android-lib
  • android implementation of IBitmap

Answer 2

The most promising IMO is to use libswscale (from FFmpeg), it offers Lanczos and many other filters. To access Bitmap buffer from native code you can use jnigraphics. This approach guarantees nice performance and reliable results.

EDIT

Here you can find rough demo app, that uses proposed approach. At the moment performance is frustratingly bad, so it should be investigated to decide if we to do something to improve it.