luminance_dither_lut.py

# gamma.py with implemented luminance curve (instead of gamma curve) 
# now embedded in the original as well
# original: http://github.com/raplin/HexaWS2811/blob/master/gamma.py
#
# more about the luminance calculations: 
# http://ledshield.wordpress.com/2012/11/13/led-brightness-to-your-eye-gamma-correction-no/ 
# http://forum.arduino.cc/index.php/topic,147810.0.html

fout=open("luminance.h","wt")

# adjust me! Each extra bit doubles the table size 
ditherBits=4

ditherMSB=1<<(ditherBits-1)

res="/* Dithered gamma correction table - autogenerated by gamma.py */\n#define DITHER_BITS %d\nconst unsigned char gammaTable[]={" % ditherBits

finalAdjust=1  #set this to 1 if you want your values to start at one (1..255). This is a quirky request for FastLED users only

for dither in range(1<<ditherBits):
    out=[]

    #reverse the low order bits so the dithering is less flickery
    ditherValue=0
    dread=1<<ditherBits
    dout=1
    for d in range(ditherBits):
        dread>>=1
        if dither & dread:
            ditherValue|=dout
        dout<<=1;
    
    ditherValue=(ditherValue<<(8-ditherBits))

    for n in range(256):
        # adjust for logarithmic eye response
        # gamma=pow(255,(n/256.0))-1
        
        # start luminance implementation ================================
        # brightness should be a value from 0 to 100
        brightnessScale = map(n,0,255,0.0,100.0)
        
        if brightnessScale>8:
            luminance = pow((brightnessScale+16.0)/116.0, 3)
        else:
            luminance = brightnessScale/903.3
            
        # luminance is a value between 0 and 1
        # we keep using the gamma variable
        gamma=luminance*256
        
        # end luminance implementation ===================================

        gamma=int(gamma*256)
        gamma+=ditherValue
        out.append( min(255, (gamma>>8)+finalAdjust) )
    if dither:
        res+=","
    res+="\n\t"+(",".join([ "0x%x"%n for n in out]))  
    
res+="\n\t};\n"

println(res);

print >>fout,res
fout.close()
exit();