[GEM-dev] Re: meanwhile, in gempixutil...

[james tittle]

On Feb 22, 2005, at 10:00 AM, IOhannes m zmoelnig wrote:

> james tittle wrote:
>> hiya,
>>
>> ...so, where'd you get these numbers from? Some kind of scaling? Is 
>> this all sounding too familiar :-)
>
> oh, and to not forget it: which "numbers" do you mean ?
> the conversion formula ?

...yeh, the following:

		  ug=88*u;
		  ub=454*u;
		  vg =  183 * v;
		  vr =  358 * v;

...I've tried to somehow reconcile them with the following conversions 
(which are what used in effectv and gem2pdp/pdp2gem currently), but 
quickly find myself feeling dumb...

/*
  * conversion from YUV to RGB
  *   r = 1.164*(y-16) + 1.596*(v-128);
  *   g = 1.164*(y-16) - 0.813*(v-128) - 0.391*(u-128);
  *   b = 1.164*(y-16)                 + 2.018*(u-128);
  * conversion from RGB to YUV
  *   y =  0.257*r + 0.504*g + 0.098*b + 16
  *   u = -0.148*r - 0.291*g + 0.439*b + 128
  *   v =  0.439*r - 0.368*g - 0.071*b + 128
  */

...so, the whole point of this was so that pdp2gem works with the 
imageStruct stuff, and then for me to altivec these things...I guess I 
can just do these equations in altivec without the worry of float 
conversions...plus altivec saturates for free (I think)!

jamie
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: text/enriched
Size: 1405 bytes
Desc: not available
URL: <http://lists.puredata.info/pipermail/gem-dev/attachments/20050222/92727cfb/attachment.bin>