Eccelerators.Matrix

src/GammaColorConverter.lvt

namespace Eccelerators.Matrix

/**
 * RGB888 transfer-curve converter. BYPASS preserves the input; SRGB decodes
 * sRGB to linear light; GAMMA22 maps normalized c to c^2.2. Tables round to the
 * nearest byte. Default/reset is bypass. Configure only between complete images.
 */
component GammaColorConverter : IColorConverter
{
	// Supported transfer curves for Configure.
	public const BYPASS: uint = 0
	public const SRGB: uint = 1
	public const GAMMA22: uint = 2

	// Active curve and immutable 256-entry transfer tables.
	curve: uint
	const SRGB_TABLE: uint[256] = [
		0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1,
		1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3,
		4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7,
		8, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 12, 12, 12, 13,
		13, 13, 14, 14, 15, 15, 16, 16, 17, 17, 17, 18, 18, 19, 19, 20,
		20, 21, 22, 22, 23, 23, 24, 24, 25, 25, 26, 27, 27, 28, 29, 29,
		30, 30, 31, 32, 32, 33, 34, 35, 35, 36, 37, 37, 38, 39, 40, 41,
		41, 42, 43, 44, 45, 45, 46, 47, 48, 49, 50, 51, 51, 52, 53, 54,
		55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70,
		71, 72, 73, 74, 76, 77, 78, 79, 80, 81, 82, 84, 85, 86, 87, 88,
		90, 91, 92, 93, 95, 96, 97, 99, 100, 101, 103, 104, 105, 107, 108, 109,
		111, 112, 114, 115, 116, 118, 119, 121, 122, 124, 125, 127, 128, 130, 131, 133,
		134, 136, 138, 139, 141, 142, 144, 146, 147, 149, 151, 152, 154, 156, 157, 159,
		161, 163, 164, 166, 168, 170, 171, 173, 175, 177, 179, 181, 183, 184, 186, 188,
		190, 192, 194, 196, 198, 200, 202, 204, 206, 208, 210, 212, 214, 216, 218, 220,
		222, 224, 226, 229, 231, 233, 235, 237, 239, 242, 244, 246, 248, 250, 253, 255
	]
	const GAMMA22_TABLE: uint[256] = [
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
		1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2,
		3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6,
		6, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 11, 11, 11, 12,
		12, 13, 13, 13, 14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19,
		20, 20, 21, 22, 22, 23, 23, 24, 25, 25, 26, 26, 27, 28, 28, 29,
		30, 30, 31, 32, 33, 33, 34, 35, 35, 36, 37, 38, 39, 39, 40, 41,
		42, 43, 43, 44, 45, 46, 47, 48, 49, 49, 50, 51, 52, 53, 54, 55,
		56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71,
		73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 84, 85, 87, 88, 89, 90,
		91, 93, 94, 95, 97, 98, 99, 100, 102, 103, 105, 106, 107, 109, 110, 111,
		113, 114, 116, 117, 119, 120, 121, 123, 124, 126, 127, 129, 130, 132, 133, 135,
		137, 138, 140, 141, 143, 145, 146, 148, 149, 151, 153, 154, 156, 158, 159, 161,
		163, 165, 166, 168, 170, 172, 173, 175, 177, 179, 181, 182, 184, 186, 188, 190,
		192, 194, 196, 197, 199, 201, 203, 205, 207, 209, 211, 213, 215, 217, 219, 221,
		223, 225, 227, 229, 231, 234, 236, 238, 240, 242, 244, 246, 248, 251, 253, 255
	]

	/**
	 * Selects a curve 0..2; invalid values leave the selection unchanged.
	 */
	public fn Configure(curve: uint) bool
	{
		if (curve > GAMMA22) {
			return false
		}

		this.curve = curve
		return true
	}

	/**
	 * Converts all channels using the selected transfer function.
	 */
	override fn Convert(rgb: logic[24]) logic[24]
	{
		if (curve == BYPASS) {
			return rgb
		}

		var value = rgb as uint
		var r = value / 65536 % 256
		var g = value / 256 % 256
		var b = value % 256

		if (curve == SRGB) {
			r = SRGB_TABLE[r as int]
			g = SRGB_TABLE[g as int]
			b = SRGB_TABLE[b as int]
		} else {
			r = GAMMA22_TABLE[r as int]
			g = GAMMA22_TABLE[g as int]
			b = GAMMA22_TABLE[b as int]
		}

		return (r * 65536 + g * 256 + b) as logic[24]
	}
}