Question

I need to convert 16-bit XRGB1555 into 24-bit RGB888. My function for this is below, but it’s not perfect, i.e. a value of 0b11111 wil give 248 as the pixel value, not 255. This function is for little-endian, but can easily be modified for big-endian.

public static Color XRGB1555(byte b0, byte b1)
{ 
    return Color.FromArgb(0xFF, (b1 & 0x7C) << 1, ((b1 & 0x03) << 6) | ((b0 & 0xE0) >> 2), (b0 & 0x1F) << 3); 
}

Any ideas how to make it work?

Answer 1

You would normally copy the highest bits down to the bottom bits, so if you had five bits as follows:

Bit position: 4 3 2 1 0
Bit variable: A B C D E

You would extend that to eight bits as:

Bit position: 7 6 5 4 3 2 1 0
Bit variable: A B C D E A B C

That way, all zeros remains all zeros, all ones becomes all ones, and values in between scale appropriately.

(Note that A,B,C etc aren’t supposed to be hex digits – they are variables representing a single bit).