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Samples directory contains some examples how to generate byte[] and save it as BMP image.

Examples

Generate Red-Green gradient square image as RGB24 bitand save it to file

public static byte[] GenerateRedGreen24BitGradient() {
	var width = 256;
	var height = 256;
	var bytesPerPixel = (int) BmpSharp.BytesPerPixelEnum.RGB24;
	var framebuffer = new byte[width * height * bytesPerPixel];

	for (var row = 0; row < height; row++) {
		for (var column = 0; column < width; column++) {
			long offset = ( row * height * bytesPerPixel ) + ( column * bytesPerPixel );
			framebuffer[offset] = 0; // blue
			framebuffer[offset + 1] = (byte) column; // green
			framebuffer[offset + 2] = (byte) row; // red
		}
	}
	return framebuffer;
}

public static void SaveGradientToBMP(){ 
	var redGreenGradient = GenerateRedGreen24BitGradient();
	var redGreenGradientBitmap = new Bitmap( 256, 256, redGreenGradient, BitsPerPixelEnum.RGB24 );
	System.IO.File.WriteAllBytes( $"{nameof( redGreenGradient )}.bmp", redGreenGradientBitmap.GetBmpBytes() );
}

something else

public static byte[] GenerateRedBlueArgb32GradientWithAlpha() {
	var width = 256;
	var height = 256;
	var bytesPerPixel = (int) BmpSharp.BytesPerPixelEnum.RGBA32;
	var framebuffer = new byte[width * height * bytesPerPixel];

	for (var row = 0; row < height; row++) {
		for (var column = 0; column < width; column++) {
			long offset = ( row * height * bytesPerPixel ) + ( column * bytesPerPixel );
			// NOTE
			// Colors in integer are in ARGB order, but BMP expect bytes in little endian order
			// So we have to store bytes array in BGRA order
			framebuffer[offset] = (byte) column; // blue
			framebuffer[offset + 1] = (byte) 0; // green
			framebuffer[offset + 2] = (byte) row; // red
			framebuffer[offset + 3] = (byte) ( ( row + column ) / 2 ); // alpha
		}
	}
	return framebuffer;
}


public static void SaveGradientToBMP(){ 
// store BMP as Red Blue gradient with Alpha channel
// NOTE : Paint and Paint.NET doesn't support Alpha channel properly !!! Use XnView or similar app

var redblueGradient = GenerateRedBlueArgb32GradientWithAlpha();
var redblueGradientBitmap = new Bitmap( 256, 256, redblueGradient, BitsPerPixelEnum.RGBA32 );
System.IO.File.WriteAllBytes( $"{nameof( redblueGradient )}.bmp" , redblueGradientBitmap.GetBmpBytes() );
}

Please note that many image viewer applications doesn't display alpha channel at all. Paint, Paint.NET, IrfanView, Visual Studio Code fails to display alpha channel properly (some fails even with RGBA PNG files, like that one above) !!!

XnView display it properly.