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author | Marcin Bukat <marcin.bukat@gmail.com> | 2011-07-19 18:29:30 +0000 |
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committer | Marcin Bukat <marcin.bukat@gmail.com> | 2011-07-19 18:29:30 +0000 |
commit | 31b7ecb09b31d7fb1e95758d5c7b3b40b38437ed (patch) | |
tree | 799714f4724ff17898c56a5e773dc0615ee58672 /firmware/target | |
parent | 5d9b23016852af99d285521f71a23ddea99ae7ee (diff) | |
download | rockbox-31b7ecb09b31d7fb1e95758d5c7b3b40b38437ed.tar.gz rockbox-31b7ecb09b31d7fb1e95758d5c7b3b40b38437ed.zip |
rk27xx - use more correct function to map between percived lightness and PWM fill factor when setting backlight brightness
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@30168 a1c6a512-1295-4272-9138-f99709370657
Diffstat (limited to 'firmware/target')
-rw-r--r-- | firmware/target/arm/rk27xx/backlight-rk27xx.c | 27 |
1 files changed, 20 insertions, 7 deletions
diff --git a/firmware/target/arm/rk27xx/backlight-rk27xx.c b/firmware/target/arm/rk27xx/backlight-rk27xx.c index e759220dff..cb669aecff 100644 --- a/firmware/target/arm/rk27xx/backlight-rk27xx.c +++ b/firmware/target/arm/rk27xx/backlight-rk27xx.c | |||
@@ -26,11 +26,24 @@ | |||
26 | #include "system.h" | 26 | #include "system.h" |
27 | 27 | ||
28 | static int brightness = DEFAULT_BRIGHTNESS_SETTING; | 28 | static int brightness = DEFAULT_BRIGHTNESS_SETTING; |
29 | static const unsigned short log_brightness[] = { | 29 | |
30 | 0x2710, 0x27ac, 0x2849, 0x2983, 0x2abd, 0x2c93, 0x2e6a, 0x30dd, | 30 | /* Based on http://www.poynton.com/PDFs/SMPTE93_Gamma.pdf |
31 | 0x3351, 0x3661, 0x3971, 0x3d1f, 0x40cc, 0x4516, 0x4960, 0x4e47, | 31 | * CIE standarized function that relates physical luminance |
32 | 0x532e, 0x58b1, 0x5e35, 0x6456, 0x6a76, 0x7134, 0x77f1, 0x7f4c, | 32 | * to perceived lightness |
33 | 0x86a6, 0x8e9d, 0x9695, 0x9f29, 0xa7bd, 0xb0ee, 0xba1f, 0xc350 | 33 | * |
34 | * L* = 116*(Y/Yn)^(1/3) - 16 (Y/Yn > 0 008856) | ||
35 | * where Yn is luminance of reference white | ||
36 | * | ||
37 | * Actual function is lightly tweaked to account for the fact | ||
38 | * that fill factor of the PWM below ~15% gives black. | ||
39 | * So the function used to calculate the values in the matrix was: | ||
40 | * f(x) = 42000 * ((100*x/31 + 16)/116)^3 + 8000 | ||
41 | */ | ||
42 | static const unsigned short lin_brightness[] = { | ||
43 | 8110, 8191, 8304, 8455, 8649, 8892, 9189, 9545, | ||
44 | 9966, 10457, 11024, 11671, 12406, 13232, 14156, 15182, | ||
45 | 16316, 17565, 18932, 20423, 22045, 23801, 25699, 27742, | ||
46 | 29937, 32289, 34803, 37485, 40340, 43374, 46592, 50000 | ||
34 | }; | 47 | }; |
35 | 48 | ||
36 | bool _backlight_init(void) | 49 | bool _backlight_init(void) |
@@ -50,7 +63,7 @@ bool _backlight_init(void) | |||
50 | /* set pwm frequency to 500Hz - my lcd panel can't cope more reliably */ | 63 | /* set pwm frequency to 500Hz - my lcd panel can't cope more reliably */ |
51 | /* (apb_freq/pwm_freq)/pwm_div = (50 000 000/500)/2 */ | 64 | /* (apb_freq/pwm_freq)/pwm_div = (50 000 000/500)/2 */ |
52 | PWMT0_LRC = 50000; | 65 | PWMT0_LRC = 50000; |
53 | PWMT0_HRC = log_brightness[brightness]; | 66 | PWMT0_HRC = lin_brightness[brightness]; |
54 | 67 | ||
55 | /* reset counter */ | 68 | /* reset counter */ |
56 | PWMT0_CNTR = 0x00; | 69 | PWMT0_CNTR = 0x00; |
@@ -88,5 +101,5 @@ void _backlight_off(void) | |||
88 | void _backlight_set_brightness(int val) | 101 | void _backlight_set_brightness(int val) |
89 | { | 102 | { |
90 | brightness = val & 0x1f; | 103 | brightness = val & 0x1f; |
91 | PWMT0_HRC = log_brightness[brightness]; | 104 | PWMT0_HRC = lin_brightness[brightness]; |
92 | } | 105 | } |