[PATCH 6/9] fbcon: Saner 16-color to 4-color conversion

[PATCH 6/9] fbcon: Saner 16-color to 4-color conversion

[Antonino A. Daplas]

    Currently, the default linux 16-colors are converted to 4-colors by simply
    dividing the values by 4.  However, this is not necessarily correct since
    the first 4 colors are converted to black, rendering them invisible.

    So, for black, no conversion; for light colors, convert to gray, for
    normal text color, no conversion, and for bright colors, convert to intense
    white.

    From: Antonino Daplas <adaplas@pol.net>
    Signed-off-by: Antonino Daplas <adaplas@pol.net>
---

 fbcon.c |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -247,9 +247,26 @@ static inline int get_color(struct vc_da
 	case 2:
 		/*
 		 * Scale down 16-colors to 4 colors. Default 4-color palette
-		 * is grayscale.
+		 * is grayscale. However, simply dividing the values by 4
+		 * will not work, as colors 1, 2 and 3 will be scaled-down
+		 * to zero rendering them invisible.  So empirically convert
+		 * colors to a sane 4-level grayscale.
 		 */
-		color /= 4;
+		switch (color) {
+		case 0:
+			color = 0; /* black */
+			break;
+		case 1 ... 6:
+			color = 2; /* white */
+			break;
+		case 7 ... 8:
+			color = 1; /* gray */
+			break;
+		default:
+			color = 3; /* intense white */
+			break;
+		}
+		break;
 	case 3:
 		/*
 		 * Last 8 entries of default 16-color palette is a more intense



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