Convert raw grayscale binary to JPEG

Question

I have C language source code, for an embedded system, containing arrays of data for an 8-bit per pixel grayscale image. I'm in charge of documenting the software and I'd like to convert this source code to a JPEG (image) file.

Here is a code sample:

const unsigned char grayscale_image[] = {
0, 0, 0, 0, 0, 0, 0, 74, 106, 159, 159, 159, 159, 159, 159, 159, 159, 159, 159, 159, 159, 159, 
159, 159, 159, 159, 159, 159, 159, 159, 159, 159, 146, 93, 39, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
//...
};
const unsigned int height = 41;
const unsigned int width = 20;

Here are my questions: (yes, plural)

1. What application(s) do you recommend for converting this source file to JPEG?
2. Can GIMP or Paint import a CSV file of data?
3. If I write this custom application, what Java libraries exist for JPEG?
4. What libraries exist in C# for accomplishing this task?

I have the following resources at my disposal: MS Visio 2010, Gimp, Paint, Java, Eclipse, MS Visual Studio 2010 Professional, wxWidgets, wxFrameBuilder, Cygwin.
I can write the custom application in C#, Java, C or C++.

Thanks for your advice.

Answer 1

The issue with using java will be to get the bytes as ints. While reading in you will need to convert to an int in order to capture values > 127 because java does not have unsigned bytes.

int height=41;
int width=20;
int[] data = {...};

BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GRAY);
for ( int x = 0; x < width; x++ ) {
  for ( int y = 0; y < height; y++ ) {
  // fix this based on your rastering order
  final int c = data[ y * width + x ];
  // all of the components set to the same will be gray
  bi.setRGB(x,y,new Color(c,c,c).getRGB() );
  }
}
File out = new File("image.jpg");
ImageIO.write(bi, "jpg", out);

Answer 2

I can answers question 4 and I can give you the code to do this in c#. It is very simple...

int width = 20, height = 41;
byte[] grayscale_image = {0, 0, 0, ...};
System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(width, height);
int x = 0;
int y = 0;
foreach (int i in grayscale_image)
{
    bitmap.SetPixel(x, y, System.Drawing.Color.FromArgb(i, i, i));
    x++;
    if (x >= 41)
    {
        x = 0;
        y++;
    }
}
bitmap.Save("output.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);

You may also be able to optimise this code if you look around for bitmap optimization techniques (such as locking the bitmap memory)

EDIT: Alternative with bit locking (should be much faster)...

NOTE: I am not 100% sure about the PixelFormat used when creating the Bitmap object - was my best guess at the options available.

int width = 20, height = 41;
byte[] grayscale_image = {0, 0, 0, ...};
System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(width, height, PixelFormat.Format8bppIndexed);

System.Drawing.Imaging.BitmapData bmpData = bitmap.LockBits(
                     new Rectangle(0, 0, bitmap.Width, bitmap.Height),
                     ImageLockMode.WriteOnly, bitmap.PixelFormat);

System.Runtime.InteropServices.Marshal.Copy(bytes, 0, bmpData.Scan0, bytes.Length);

bitmap.UnlockBits(bmpData);

return bitmap;

Answer 3

You can just use the ImageIO class in java.

BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GREY);

Graphics2D g2 = bi.createGraphics();

//loop through and draw the pixels here   

File out = new File("Myimage.jpg");
ImageIO.write(bi, "jpg", out);