Help processing a byte[] of packed (24-bit) RGB values

Question

I'm having some difficulty converting a byte[] of RGB values to a JPEG using the ImageIO classes. The byte[] contains 24-bit RGB values and I'd like to somehow get this data into a format that can be saved to a JPEG File (presumably with JPEGImageEncoder?)
Any advice on where to get started would be greatly appreciated!

Answer 1

the ImageIO class wants a BufferedImage, which in my opinion is the easiest way to work with image files.
You first construct a BufferedImage object, like this:
BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);Width and height you should know, they are the dimensions of the image in pixels.
You can use the setRGB() method to set a single pixel of the image, something like this:
byte[] rgb; // get this somewhere, it is your byte array of RGB values
// index into the rgb array
int i = 0;
for(int y = 0; y < height; y++){
     for(int x = 0; x < width; x++, i+= 3){
          byte a = 0;
          byte r = rgb;
          byte g = rgb[i+1];
          byte b = rgb[i+2];
          int pix = ((a << 24) + (r << 16) + ([g << 8) + b);
          img.setRGB(x,y,pix);
This is typed from memory, I may have made a mistake somewhere. Right now I assume the byte array contains only RGB components, that's why I leave alpha 0. If you ever have a 32 bit image, you can adapt this code easily.
After you have the BufferedImage, you can simply write it as a JPEG file using ImageIO.write().