[PD] Pix_levels explanation and Screen Effect for Gem

[james tittle]

On Apr 5, 2006, at 5:55 AM, Peter Forde wrote:

> In Gem, does anyone know how pix_levels works. I just want to kill  
> all the reds or greens in a video. I don't understand the floor/ 
> ceiling stuff.

...ok, no one answered how pix_levels works, so I'll try...it's alot  
like the "levels" option in Gimp or photo$hop:  they all allow you to  
control the levels of color channels, either individually or together...

...[pix_levels] has a few different modes:  auto, auto+uniform,  
uniform, and "other"...when "auto" is on, the object automagically  
assumes it knows most of the bandwidth you'd like to deal with, and  
so you really just need to tell it what to do with individual  
channels...for example, if you just want to remove the red channel,  
set auto on, then send [0 1 0 0< to the third inlet...(this reminds  
me that it might be better to have a named message here, so maybe in  
the future we can have a [red 0 1 0 0< to do the same thing)

...the uniform mode takes one message for the RGB channels together,  
and this goes to the 2nd inlet of [pix_levels]...this works more as  
an overall lightness/darkness control for the image...

...the floor/ceiling stuff has to do with how much bandwidth of the  
color(s) you're dealing with, and you usually have seperate in/out  
floor/ceilings...so, if you have [0 1 0 1<, you have the full  
spectrum of the channel output...

hth,

james