arduino_rgb_led/gamma.py

   1 # https://github.com/raplin/HexaWS2811/blob/master/gamma.py
   2 # Lookup table generator
   3 #
   4 # Really it's correcting for the eye's luminance response, it's not actually gamma correction (it's misnamed!)
   5 #
   6 # We're generating a set of 256-entry lookup tables which you use to (separately) convert the 8-bit R, G and B components of your color
   7 # into something you output, typically with an intelligent RGB LED such as a WS2812B; but a simple CPU-based PWM will give the same results (and benefit from this correction)
   8 #
   9 # We generate several sets  (2,4,8...) of 256-entry tables so you can cycle through them, using a successive 8-bit lookup table each successive output frame.
  10 # This is 'temporal dithering', which aims to give you better color resolution at the dark end of the scale.
  11 # If you update at e.g. 100hz, try using two or three 'ditherBits' (i.e. 2^^2 or 2^^3=8 tables. The faster your update the more tables you can use
  12 # and you get better color resolution. More than 5 ditherbits is probably excessive, even 2 will help somewhat.
  13 #
  14 # If you get objectionable flickering when displaying low-intensity pixels, you should either update your leds faster or reduce ditherBits
  15 #
  16 #
  17 #
  18 fout=open("gamma.h","wt")
  19
  20 #adjust me! Each extra bit doubles the table size
  21 ditherBits=1
  22
  23 ditherMSB=1<<(ditherBits-1)
  24
  25 res="/* Dithered luminance correction table - autogenerated by gamma.py */\n#define DITHER_BITS %d\nconst prog_uchar PROGMEM gammaTable[]={" % ditherBits
  26
  27 useRealLuminanceCalcuation=True # CIE 1931 formula
  28
  29 finalAdjust=0  #set this to 1 if you want your values to start at one (1..255). This is a quirky request for FastLED users only
  30
  31 for dither in range(1<<ditherBits):
  32     out=[]
  33
  34     #reverse the low order bits so the dithering is less flickery
  35     ditherValue=0
  36     dread=1<<ditherBits
  37     dout=1
  38     for d in range(ditherBits):
  39         dread>>=1
  40         if dither & dread:
  41             ditherValue|=dout
  42         dout<<=1;
  43
  44     ditherValue=(ditherValue<<(8-ditherBits))
  45
  46     for n in range(256):
  47         if useRealLuminanceCalcuation:
  48             # CIE 1931
  49             brightness=n/2.56
  50             if brightness > 8:
  51                 pwmValue= pow( ((brightness + 16) / 116) , 3  )
  52             else:
  53                 pwmValue = brightness / 903.3
  54             pwmValue*=256
  55         else:
  56             #use simple power
  57             pwmValue=pow(255,(n/256.0))-1
  58         pwmValue=int(pwmValue*256)
  59         pwmValue+=ditherValue
  60         pwmValue=min(255, (pwmValue>>8)+finalAdjust)
  61         out.append( pwmValue )
  62     if dither:
  63         res+=","
  64     res+="\n\t"+(",".join([ "0x%x"%n for n in out]))
  65
  66 res+="\n\t};\n"
  67
  68 print >>fout,res
  69 fout.close()