Image thumbnail in an optimized way for J2Me platform

 Trying to show thumbnail view after taking a big snapshot ? Trying to show a list view of images ? Or in any other case you try to resize or scale an image ?

I was searching for an optimized code for thumbnail creation. The main issues here are

- You need to be careful about the memory you use. After taking a big image in memory you may have a little left for allocation.
- You do not have floating point in most of the mobiles. So your image may not keep the image ratio right after scaling.
- Your need very time efficient code , you can keep the image quality apart ..

I did some google. And found the following discussions useful.

http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=41&t=002988
http://developer.sonyericsson.com/thread/27493

I tested some of those examples. Some of them cause OutOfMemory Exception. Some take a long time to resize image. But I thought I could do better. Finally I wrote the following code.

    /**
 * Gets the thumbnail that fit with given screen width, height and padding ..
 *
 * @param image The source image
 * @param padding padding to the screen
 * @return scaled image
 */
    private final Image getThumbnailWrapper(Image image, int expectedWidth, int expectedHeight, int padding) {
     final int sourceWidth = image.getWidth();
  final int sourceHeight = image.getHeight();
     int thumbWidth = -1;
  int thumbHeight = -1;

  // big width
  if(sourceWidth >= sourceHeight) {
   thumbWidth = expectedWidth - padding;
   thumbHeight = thumbWidth * sourceHeight / sourceWidth;
   // fits to height ?
   if(thumbHeight > (expectedHeight - padding)) {
    thumbHeight = expectedHeight - padding;
    thumbWidth = thumbHeight * sourceWidth / sourceHeight;
   }
  } else {
   // big height
   thumbHeight = expectedHeight - padding;
   thumbWidth = thumbHeight * sourceWidth / sourceHeight;
   // fits to width ?
   if(thumbWidth > (expectedWidth - padding)) {
    thumbWidth = expectedWidth - padding;
    thumbHeight = thumbWidth * sourceHeight / sourceWidth;
   }
  }

  // XXX As we do not have floating point, sometimes the thumbnail resolution gets bigger ...
  // we are trying hard to avoid that ..
  thumbHeight = (sourceHeight < thumbHeight) ? sourceHeight : thumbHeight;
  thumbWidth = (sourceWidth < thumbWidth) ? sourceWidth : thumbWidth;

  return getThumbnail(image, thumbWidth, thumbHeight);
    }

    /**
 * Gets thumbnail with a height and width specified ..
 * @param image
 * @param thumbWidth
 * @param thumbHeight
 * @return scaled image
 */
    private final Image getThumbnail(Image image, int thumbWidth, int thumbHeight) {
  int x, y, pos, tmp, z = 0;
  final int sourceWidth = image.getWidth();
  final int sourceHeight = image.getHeight();

  // integer ratio ..
  final int ratio = sourceWidth / thumbWidth;

  // buffer where we read in data from image source
  final int[] in = new int[sourceWidth];

  // buffer of output thumbnail image
  final int[] out = new int[thumbWidth*thumbHeight];

  final int[] cols = new int[thumbWidth];

  // pre-calculate columns we need to access from source image
  for (x = 0,pos = 0; x < thumbWidth; x++) {
   cols[x] = pos;

   // increase the value without fraction calculation
   pos += ratio;
   tmp = pos + (thumbWidth - x) * ratio;
   if(tmp > sourceWidth) {
    pos--;
   } else if(tmp < sourceWidth - ratio) {
    pos++;
   }
  }

  // read through the rows ..
  for (y = 0, pos = 0, z = 0; y < thumbHeight; y++) {

   // read a single row ..
   image.getRGB(in, 0, sourceWidth, 0, pos, sourceWidth, 1);

   for (x = 0; x < thumbWidth; x++, z++) {
    // write this row to thumbnail
    out[z] = in[cols[x]];
   }

   pos += ratio;
   tmp = pos + (thumbHeight - y) * ratio;
   if(tmp > sourceHeight) {
    pos--;
   } else if(tmp < sourceHeight - ratio) {
    pos++;
   }
  }
  return Image.createRGBImage(out, thumbWidth, thumbHeight, false);
}

This code has low memory need as it only reads one row from the source image each time. And it is super fast (I mean unbelievable).

 

come from: http://miniim.blogspot.com/2008/05/image-thumbnail-in-optimized-way-for.html