Re: Color Reference of NTSC Formula?

["Bryan Parkoff" <nospam@nospam.com>]

"Mark McDougall" <markm@vl.com.au> wrote in message 
news:44cdbde0$0$1513$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
> Bryan Parkoff wrote:
>
>>     Think about Deep Red, Dark Blue, and Purple.  You display Deep Red.
>> Then, you want to display Purple instead of Deep Red.  You have to add 
>> Dark
>> Blue to the screen.  It is like Deep Red and Dark Blue are joined 
>> together
>> like "OR" to become Purple.  Deep Red "OR" Dark Blue = Purple.
>
> I think your logic is not quite valid for a system based on luminance
> and chrominance. You can think this way for RGB because it is 'additive'
> - adding and subtracting components of R,G & B give you colours ranging
> from black to white.
>
> From my limited understanding, the phase shift as you move around the
> colour wheel is directly related to wavelength. You can't simply add
> phase offsets together to give the colour that corresponds to the sum of
> the angles.

Hello Mark,

    Thank you again.  Yes, I have read an explanation already before you 
provided me the website address.  It is complicated for me to understand.  I 
do understand how color in a circle works that is opposed to color in a 
square.  Think of color in a square.  It is truly RGB.  Darkness color is in 
the bottom of this square and brightness color is in the top of this square. 
You fill 0-255 value on R, G, and B signal.  It allows the line of RGB to be 
moving from the bottom to the top of this square until you get the correct 
color.
    Think of color in a circle what I am referring Deep Red, Dark Blue, Dark 
Green, and Brown.  Apple IIgs attempts to emulate a color in the circle to 
display HGR and DHGR using phase shift by the following 0 to 360 degree. 
You place one bit on position 0 and three zero bits on position 1 through 3 
of DHGR.  The phase shift is on 0 degree.  It displays Deep Red pixel.  It 
is where an arrow in the color circle is pointed to the 0 degree.
    You want Dark Blue instead of Deep Red.  You have to move the arrow from 
0 degree to 90 degree in the color circle by clearing a bit in position 0 
and setting a bit in position 1.  It looks like 0100 instead of 1000.  It is 
now 90 degree instead of 0 degree.  Deep Red pixel became Dark Blue pixel. 
It does the same process to clearing and setting bit.  It is like a bit is 
moving from phase shift to phase shift.  1000, 0100, 0010, 0001, 1000.
    You can see Dark Blue changed to Dark Green at 180 degree.  It does the 
same for Dark Green changed to Brown at 270 degree.  Again, it is changing 
from Brown to Deep Red at 360 degree.  It is at 360 degree that is pointing 
at 0 degree.  It continues to run a wheel like color circle while four 
different color pixels are rolling like a wheel on the horizontial line.  It 
does the same example for a group of Purple, Blue, Green, and Orange, a 
group of Dark Gray, and Light Gray, and also a group of Light Blue, 
Aquamarine, Yellow, and Pink.
    Do you know what I mean?

>>     It is what I am trying to translate number of degrees to 16 
>> individual
>> color RGB pixels.
>>     Do you know what I am trying to clarify in details?  Do you know the
>> formula or equation?
>
> Have you read this..
> <http://www.ee.washington.edu/conselec/CE/kuhn/ntsc/95x4.htm>
>
> It should have the information you need.

    Do you agree what I provided 16 colors in a table with 4 bits and 
degree?  Is it wrong?

> eg. Looking at the Vector Scope reference I link in my previous post...
> For RED, Q = 0.21, I = 0.6.
> Theta = atan(0.21/0.6) = 19.3 deg.
> Now I axis is 57 deg from the burst = 123 deg.
> So RED = 123 - 19.3 = 103.7 deg.
> Which corresponds to RED on the "VECTOR SCOPE".
>   Similarly for yellow... Q=0.21-0.52=-0.31, i=0.6-0.28=0.32
> Theta = atan(-0.31/0.32) = -44 deg.
> Yellow = 123 - (-44) = 167 deg.
>   etc.

    How do you get the value of Q and I with your knowledge?  Do you guess 
the values by trying to pick up the correct degree for the color?  For an 
example, I is orange and Q is green.  It is what you intend to display 
orange pixel.  Use 10X to 30X magnifier at the NTSC monitor where it is 
orange pixel.  You may be able to see red dot light, green dot light, and 
blue dot light behind the window of NTSC monitor so you can see strip of 
orange and green.  You might notice Deep Red in the left.
    You intend to translate a group of phase shift or four pulses to four 
individual RGB pixels.  How?  Without formula?  It is possible to guess by 
translating orange strip and green strip into two orange pixels and two 
brown pixels of RGB.  I am curious how Apple Computer, Inc knows to do with 
RGB DHGR from NTSC.  It is what I observed my oscilliscope equipment when I 
captured all the DHGR's pixel structure into DHGR table.  It is a success, 
but it has 8% error because of color misalignment in the pixel structure. 
It is not my design in error, but it is the way how logic is used.
    The only way is to solve 8% error which it has to follow phase shift 
with color circle and degree formula to RGB.  If it is impossible, I would 
add correction status in the DHGR table.  It will detect error and correct 
color misalignment in the pixel structure automatically.  My screenshot of 
DHGR pictures from Microsoft Paint looks identical 100% to the true Apple 
IIgs' screen on VGA monitor unlikely KEGS32 and AppleWin.

Bryan Parkoff