Pixel value for 16 bits grayscale images

Question

I know this is mostly an image question not code, but I'll give it a shot here.

So first I have a 8bits/pixel grayscale image(bitmap). Which means that each pixel is represented into 1 byte. This means that the the pixel value is the byte value. Clear enough.

But then...

I have a 16bits/pixel grayscale image (bitmap). Which means that each pixel is represented into 2 bytes. This is clear for me. Now I create a byte[] array that will hold each byte value.

For an 1024x1024 image I will have 2097152 bytes. It's 1024*1024*2.

My question is now, how do I get the pixel value for a specific pixel.

Let's say for pixel at position(X|Y) the bytes are 84 and 77. How do I transform these 2 values into the pixel value.

Firstly I need this for some calculation where I need the pixel value, then I want to change the color palette of the bitmap and it works fine with 8 bitsperpixel images, but doesn't for 16bitsperpixel images.

Any help would be nice.

 var width = bitmap.PixelWidth;
            var height = bitmap.PixelHeight;
            var dpiX = bitmap.DpiX;
            var dpiY = bitmap.DpiY;

            byte[] pixels = new byte[
                     bitmap.PixelHeight * bitmap.PixelWidth *
                         bitmap.Format.BitsPerPixel / 8];

            bitmap.CopyPixels(pixels, bitmap.PixelWidth * bitmap.Format.BitsPerPixel / 8, 0);

This is how I create the array of pixels.

Answer 1

It may be easier to use a 2-byte type for the pixel array:

var width = bitmap.PixelWidth;
var height = bitmap.PixelHeight;
var pixels = new ushort[width * height];

bitmap.CopyPixels(pixels, 2 * width, 0);

Access an individual pixel value directly from that array:

var x = 100;
var y = 200;
var pixel = (int)pixels[width * y + x];

In order to convert the 16bpp pixel array into a 8bpp array, just divide each pixel value by 256

var pixels8bpp = pixels.Select(p => (byte)(p / 256)).ToArray();

and create a 8bpp BitmapSource by

var bitmap8bpp = BitmapSource.Create(
    width, height, 96, 96, PixelFormats.Gray8, null, pixels8bpp, width);