From 719dcaefe09ecf538546a54cc8e0a9646f7cb17e Mon Sep 17 00:00:00 2001
From: Solomon Peachy <pizza@shaftnet.org>
Date: Wed, 3 Jan 2018 21:00:57 -0500
Subject: magicard:  Implement gamma correction.

The output looks pretty decent now!
---
 backend_magicard.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 74 insertions(+), 5 deletions(-)

diff --git a/backend_magicard.c b/backend_magicard.c
index 150ebd3..6a60d8a 100644
--- a/backend_magicard.c
+++ b/backend_magicard.c
@@ -47,6 +47,66 @@
 #define USB_VID_MAGICARD     0x0C1F
 #define USB_PID_MAGICARD_TANGO2E 0x1800
 
+/* Gamma tables computed with this perl program:
+
+  my $input_bpp = 8;
+  my $output_bpp = 6;
+  my $gamma = 1/1.8;  # or 1/2.2 or whatever.
+
+  my $i;
+
+  for (my $i = 0 ; $i < (2 ** $input_bpp) ; $i++) {
+    my $linear = $i / (2 ** $input_bpp);
+    my $gc = ($linear ** $gamma) * (2 ** $output_bpp);
+    $gc = int($gc);
+    print "$gc, ";
+  }
+
+*/
+
+static uint8_t gammas[2][256] = {
+	/* Gamma = 2.2 */
+	{
+		 0,  5,  7,  8,  9, 10, 11, 12, 13, 13, 14, 15, 15, 16, 17,
+		17, 18, 18, 19, 19, 20, 20, 20, 21, 21, 22, 22, 23, 23, 23,
+		24, 24, 24, 25, 25, 25, 26, 26, 26, 27, 27, 27, 28, 28, 28,
+		29, 29, 29, 29, 30, 30, 30, 31, 31, 31, 31, 32, 32, 32, 32,
+		33, 33, 33, 33, 34, 34, 34, 34, 35, 35, 35, 35, 35, 36, 36,
+		36, 36, 37, 37, 37, 37, 37, 38, 38, 38, 38, 38, 39, 39, 39,
+		39, 39, 40, 40, 40, 40, 40, 41, 41, 41, 41, 41, 42, 42, 42,
+		42, 42, 43, 43, 43, 43, 43, 43, 44, 44, 44, 44, 44, 45, 45,
+		45, 45, 45, 45, 46, 46, 46, 46, 46, 46, 47, 47, 47, 47, 47,
+		47, 48, 48, 48, 48, 48, 48, 48, 49, 49, 49, 49, 49, 49, 50,
+		50, 50, 50, 50, 50, 50, 51, 51, 51, 51, 51, 51, 51, 52, 52,
+		52, 52, 52, 52, 52, 53, 53, 53, 53, 53, 53, 53, 54, 54, 54,
+		54, 54, 54, 54, 55, 55, 55, 55, 55, 55, 55, 56, 56, 56, 56,
+		56, 56, 56, 56, 57, 57, 57, 57, 57, 57, 57, 57, 58, 58, 58,
+		58, 58, 58, 58, 58, 59, 59, 59, 59, 59, 59, 59, 59, 60, 60,
+		60, 60, 60, 60, 60, 60, 61, 61, 61, 61, 61, 61, 61, 61, 62,
+		62, 62, 62, 62, 62, 62, 62, 62, 63, 63, 63, 63, 63, 63, 63, 63,
+	},
+	/* Gamma = 1.8 */
+	{
+		  0,  2,  4,  5,  6,  7,  7,  8,  9,  9, 10, 11, 11, 12, 12,
+		 13, 13, 14, 14, 15, 15, 15, 16, 16, 17, 17, 17, 18, 18, 19,
+		 19, 19, 20, 20, 20, 21, 21, 21, 22, 22, 22, 23, 23, 23, 24,
+		 24, 24, 24, 25, 25, 25, 26, 26, 26, 26, 27, 27, 27, 28, 28,
+		 28, 28, 29, 29, 29, 29, 30, 30, 30, 30, 31, 31, 31, 31, 32,
+		 32, 32, 32, 33, 33, 33, 33, 34, 34, 34, 34, 34, 35, 35, 35,
+		 35, 36, 36, 36, 36, 36, 37, 37, 37, 37, 37, 38, 38, 38, 38,
+		 39, 39, 39, 39, 39, 40, 40, 40, 40, 40, 41, 41, 41, 41, 41,
+		 42, 42, 42, 42, 42, 42, 43, 43, 43, 43, 43, 44, 44, 44, 44,
+		 44, 45, 45, 45, 45, 45, 45, 46, 46, 46, 46, 46, 47, 47, 47,
+		 47, 47, 47, 48, 48, 48, 48, 48, 48, 49, 49, 49, 49, 49, 49,
+		 50, 50, 50, 50, 50, 50, 51, 51, 51, 51, 51, 51, 52, 52, 52,
+		 52, 52, 52, 53, 53, 53, 53, 53, 53, 54, 54, 54, 54, 54, 54,
+		 55, 55, 55, 55, 55, 55, 55, 56, 56, 56, 56, 56, 56, 57, 57,
+		 57, 57, 57, 57, 57, 58, 58, 58, 58, 58, 58, 58, 59, 59, 59,
+		 59, 59, 59, 60, 60, 60, 60, 60, 60, 60, 61, 61, 61, 61, 61,
+		 61, 61, 62, 62, 62, 62, 62, 62, 62, 63, 63, 63, 63, 63, 63, 63,
+	}
+};
+
 /* Private data structure */
 struct magicard_ctx {
 	struct libusb_device_handle *dev;
@@ -397,9 +457,18 @@ static void downscale_and_extract(int gamma, uint32_t pixels,
 		uint8_t b_shift;
 
 		/* Downscale color planes from 8bpp -> 6bpp; */
-		y = *y_i++ >> 2;
-		m = *m_i++ >> 2;
-		c = *c_i++ >> 2;
+		if (gamma) {
+			if (gamma > 2)
+				gamma = 2;
+			gamma--;
+			y = gammas[gamma][*y_i++];
+			m = gammas[gamma][*m_i++];
+			c = gammas[gamma][*c_i++];
+		} else {
+			y = *y_i++ >> 2;
+			m = *m_i++ >> 2;
+			c = *c_i++ >> 2;
+		}
 
 		/* Extract "true black" from ymc data, if enabled */
 		if (k_o && y == 0x3f && m == 0x3f && c == 0x3f) {
@@ -763,7 +832,7 @@ static int magicard_cmdline_arg(void *vctx, int argc, char **argv)
 
 struct dyesub_backend magicard_backend = {
 	.name = "Magicard family",
-	.version = "0.07",
+	.version = "0.08",
 	.uri_prefix = "magicard",
 	.cmdline_arg = magicard_cmdline_arg,
 	.cmdline_usage = magicard_cmdline,
@@ -913,7 +982,7 @@ struct dyesub_backend magicard_backend = {
 
     Commands consumed by backend:
 
-  ICC%d    Gamma curve (0, 1, 2) -- NOT IMPLEMENTED YET
+  ICC%d    Gamma curve (0, 1, 2) -- off, 2.2, or 1.8 respectively.
   X-GP-8   Raw data is 8bpp. needs to be converted.
   X-GP-RK  Extract K channel from color data.
 
-- 
cgit v1.2.1