Android stream multiple bitmap tiles to single jpeg file

Question

I am developing an image manipulation application which has to be able to work on large images e.g. those taken by a camera, the approach I'm taking is to split the source image into multiple suitably sized tiles so that the tiles can be loaded individually into memory as a Bitmap without exceeding the dreaded VM limit, next image manipulation is performed on a tile by tile basis, this is all well and good but until I want to stitch these tiles back to a final jpeg image.
I'm looking for a built in sdk api or free ware solution that can perform the following:

Open jpeg output file as output stream

Stream RGB pixels from bitmap (tile 1) to jpeg output stream

Stream RGB pixels from bitmap (tile 2) to jpeg output stream

etc.. for all tiles

Close jpeg output stream

Any ideas or pointers other than writing my own jpeg encoder?

Just out of curiosity, how do you slice the images in the beginning? — Dan S
I use BitmapRegionDecoder with a Rect indicating the region of the source (big bitmap/jpeg) that I want to grab, e.g. if my source image is 2000x2000 pixels and I want 4 tiles the first tile would be (0,0)-(1000,1000), second would be (1000,0)-(2000,1000), third (0,1000)-(1000,2000) and fourth (1000,1000)-(2000,2000). I process these one by one and save off to temporary bitmaps on the sdcard, the problem is then stitching these back to form a final image (preferably a jpeg). — Daryl Hurst

dbryson dbryson · Accepted Answer · 2012-02-29T22:36:43

What about this:

FileOutputStream outFile = new FileOutputStream(output_file);
bitmap.compress(Bitmap.CompressFormat.JPEG, 100, outFile);
outFile.flush();
outFile.close();

You can adjust the quality setting (100). See the docs

You'll still need to decide how to slice it. But if you're taking the image on the device, why would it be a problem loading the whole image if it didn't cause a memory problem in the first place?

Stitching Tiles back together: Here's one simple approach used by slippy maps the I know works.

Cut tiles in standard size (say 256x256)
Assign each tile an x,y value - this could be a directory structure or filename convention: i.e. "0_0.jpg"
Tile names (numbers) are related to their top/left pixel position.

Each tile number can be calculated by the following:

tileX = floor(pixelX / 256)

tileY = floor(pixelY / 256)

So the tile at pixels 0,0 = tile (0,0), the tile at pixels 256,0 is tile (1,0), etc...

Android stream multiple bitmap tiles to single jpeg file

2 Answers