Subject: Re: [stella] tia hue luminance From: Adam Wozniak <adam@xxxxxxxxxxxxxxxx> Date: Sat, 6 Dec 2003 09:06:01 0800 (PST) 
On Fri, 5 Dec 2003, Eric Ball wrote: > Note: R'G'B' are nonlinear values which should be limitted to the range > 0.0  1.0 and represent the voltage used to drive the CRT guns. Linear RGB > requires a gamma correction of 2.2 from R'G'B'. As with every conversion I've ever seen posted here, the equations yeild values below zero and above 1. Do you clip these? Scale them? Here are some examples: COLU R' G' B' 16 0 .283 .428 158 1.35 .055 1.818 The problem always lies here: > R' = 1.140V' + Y' > B' = 2.033U' + Y' > G' = Y'  0.3947U'  0.5808V' > Y' = 0.1 * ( COLU AND 15 ) > hue = 180 degrees  ( COLU / 16  1 ) * 24 degrees > saturation = 0 if ( COLU / 16 == 0 ), otherwise saturation = 40/190 > U' = saturation * cos ( hue ) > V' = saturation * sin ( hue ) U' and V' can range from 0 to +/ 0.2105 Y' can range from 0 to 1.5 In a worst case U'=0.215 and Y'=0, B' =2.033*0.2105+0 = 0.428 Which is about what you see for COLU=16 At first I thought it would work out if you could just pick the right value for saturation, but Y' can always be zero, meaning there is always a way to get R', G', or B' to be negative. There are similar problems on the high end too. Using your equations, I get 0.23869 < R' < 1.6386 0.14744 < G' < 1.5464 0.42794 < B' < 1.8186 Which doesn't jive at all with: > Note: R'G'B' are nonlinear values which should be limitted to the range > 0.0  1.0 and represent the voltage used to drive the CRT guns. Linear RGB > requires a gamma correction of 2.2 from R'G'B'. So do these get clipped or scaled or what?  adam@xxxxxxxxxxxxxxxx http://cuddlepuddle.org/~adam/pgp.html Will code for food. http://cuddlepuddle.org/~adam/resume.html "The dinosaurs are not around today because they did not have a space program."  Arthur C. Clarke  Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
Current Thread 


< Previous  Index  Next > 

Re: [stella] tia hue luminance, Eric Ball  Thread  Re: [stella] tia hue luminance, Eric Ball 
Re: [stella] TIA polynomials revisi, Adam Wozniak  Date  Re: [stella] New home for TheDig, KirkIsrael 
Month 