Photo Mosaic Algorithm. How to create a mosaic photo given the basic image and a list of tiles?

Question

Hy.What I have to do is to create a program (using C or C++), that takes as input a 24bits/pixel bitmap and a gathering of images and I have to create a mosaic image , similar to the input image using the library of images given(To create a mosaic Photo similar to the input).

So far I can access the input's image pixels and the colors from it but I'm kind of stuck. My question is Where should I start? I need a basic algorithm that could do such a thing. And I can't really find any(maybe I'm looking wrong). And also can someone tell me a random photo downloader, so that i can download small images for the project? Can someone help me? Please, tell me where to start and what to use.

Answer 1

I've done this in Scala. The Dr Dobbs article was extremely useful to me.

Sample image:

Here's my basic algorithm:

def createMosaic(targetImage:BufferedImage,
  index:PhotoIndexer.PhotoIndex,
  opacity:Float,
  targetWidth:Int,
  targetHeight:Int,
  numRows:Int,
  numColumns:Int, callback:PhotoMosaicCallback): ImageGrid = {

      var indexCopy = index

      // Map from the buffered image to that image's average color
      var colorMap:Map[BufferedImage,Color] =
      index.values.map(data => (data.thumbnail, data.avgColor)).toMap

      // We look at rectangular regions of the target image, calculate their average
      // colors, and then pick images that match those colors.
      val sampleWidth = targetImage.getWidth / numColumns
      val sampleHeight = targetImage.getHeight / numRows

      // Used to report the progress of the process
      var counter = 1
      val numSubImages = numRows * numColumns

      val imageGrid:ImageGrid = Array.fill(numRows, numColumns)(Nil)

      // for each patch in the image
      for (row <- 0 until numRows) {
        for (column <- 0 until numColumns) {
          val x = column * sampleWidth
          val y = row * sampleHeight
          // This is the small rectangular region of the target image that we're
          // currently considering
          val subImage = targetImage.getData(new Rectangle(x,y,sampleWidth,sampleHeight))
          val avgImageColor = calculateColorFromRaster(subImage)

          val nearest:Seq[BufferedImage] = getNearestColorImages(avgImageColor, colorMap)

          // nearest is in sorted order; pick one of them and draw it to correct place in
          // image
          imageGrid(row)(column) = nearest

          callback.photosCalculated(row, column, nearest)

          val percent = 100.0 * counter / numSubImages
          // TODO: for GUI version, use a display bar
          if (counter % 100 == 0) {
            println(percent + " completed (" + counter + " of" + numSubImages + ")")
          }
          counter+=1
        }
      }
      imageGrid
}

My full sourcecode is available on github