Fast way to compress binary data?

I have some binary data (pixel values) in a int[] (or a byte[] if you prefer) that I want to write to disk in an Android app. I only want to use a small amount of processing time but want as much compression as I can for this. What are my options?

In many cases the array will contain lots of consecutive zeros so something simple and fast like RLE compression would probably work well. I can't see any Android API functions for this though. If I have to loop over the array in Java, this will be very slow as th开发者_运维知识库ere is no JIT on most Android devices. I could use the NDK but I'd rather avoid this if I can.

DeflatorOutputStream takes ~25 ms to compress 1 MB in Java. Its a native method so a JIT should not make much difference.

Do you have a requirement which says 0.2s or 0.5s is too slow?

Can you do it in a background thread so the user doesn't notice how long it takes?

GZIP is based on the Deflator + CRC32 so is likely to be much the same or slightly slower.

Deflator has several modes. The DEFAULT_STRATEGY is fastest in Java, but simpler compressions such as HUFFMAN_ONLY might be faster for you.

Android has Java's DeflaterOutputStream. Would that work?

Pass the byte array to
http://download.oracle.com/javase/6/docs/api/java/io/FileWriter.html
and chain
http://download.oracle.com/javase/1.4.2/docs/api/java/util/zip/GZIPOutputStream.html to it

then when you need to read the data back in do the reverse http://download.oracle.com/javase/1.4.2/docs/api/java/io/FileReader.html
and chain
http://download.oracle.com/javase/1.4.2/docs/api/java/util/zip/GZIPInputStream.html

Depending on the size of the file your saving you will see some compression Gzip is good like that, if your not seeing much of a trade of just write the data uncompressed using a buffered writer(That should be the fastest). Also if you do gzip it using a buffered writer reader could also speed it up a bit.

I've had to solve basically the same problem on another platform and my solution was to use a modified LZW compression. First, do some difference filtering (similar to PNG) on the 32bpp image. This will turn most of the image to black if there are large areas of common color. Then use a generic GIF compression algorithm treating the filtered image as if it's 8bpp. You'll get decent compression and it works very quickly. This will need to run in native code (NDK). It's really quite easy to get native code working on Android.

Random thought: if it's image data, try saving it as png. Standard java has it, i'm sure android will too, and probably optimized with native code. It has pretty good compression and it's lossless.