Need help with RGB -> CMYK

Need help with RGB -> CMYK

Post by Bryan Horli » Wed, 26 Jun 1996 04:00:00



I've got a formula that theoretically converts an RGB color value to a
CMYK value.  The trouble is, of course, that it doesn't work (as tested by
comparing the original RGB to the new CMYK color in Photoshop).  So here's
what I'm using:

RGB -> CMY
   C = 1 - R
   M = 1 - G
   Y = 1 - B

CMY -> CMYK
   K = min (C, M, Y)
   C = (C - K) / (1 - K)
   M = (M - K) / (1 - K)
   Y = (Y - K) / (1 - K)

This was taken from a web-faq on color spaces.  Does anyone know of a more
accurate way of doing this?  Is this in vain?

On another note...does anyone know of a way to convert an RGB value to
it's Pantone equivalent?  Somehow I doubt it, but it's worth a shot.

Thanks for any help..

Bryan Horling

 
 
 

Need help with RGB -> CMYK

Post by Andrew Rode » Fri, 28 Jun 1996 04:00:00


Quote:> This was taken from a web-faq on color spaces.  Does anyone know of a more
> accurate way of doing this?  Is this in vain?

It is kind of in vain in that CMYK is device dependant. Each CMYK device
will work differently. You have to take into account the black channel,
and if going out to a press issues like UCR/GCR. You really can1t work
with such a simplistic formula. This is the cool thing about a good color
management system like that from Kodak. It takes a monitor reference color
space and converts to CMYK based on output profiles specific to different
CMYK devices.

Andrew Rodney
www.camera-darkroom.com

 
 
 

Need help with RGB -> CMYK

Post by Chris C » Sat, 29 Jun 1996 04:00:00




>> This was taken from a web-faq on color spaces.  Does anyone know of a more
>> accurate way of doing this?  Is this in vain?

>It is kind of in vain in that CMYK is device dependant. Each CMYK device
>will work differently. You have to take into account the black channel,
>and if going out to a press issues like UCR/GCR. You really can1t work
>with such a simplistic formula. This is the cool thing about a good color
>management system like that from Kodak. It takes a monitor reference color
>space and converts to CMYK based on output profiles specific to different
>CMYK devices.

>Andrew Rodney
>www.camera-darkroom.com

Don't forget that RGB is also very much device dependent (as anyone who
has created graphics on a Macintosh and tried viewing them on a PC knows).

Chris
--
Companies have policies, not opinions.
Thus my opinions cannot be those of my company.
http://www.asi.com/powershop/pwrshop.html

 
 
 

1. Need help with RGB -> CMYK

I've got a formula that theoretically converts an RGB color value to a
CMYK value.  The trouble is, of course, that it doesn't work (as tested by
comparing the original RGB to the new CMYK color in Photoshop).  So here's
what I'm using:

RGB -> CMY
   C = 1 - R
   M = 1 - G
   Y = 1 - B

CMY -> CMYK
   K = min (C, M, Y)
   C = (C - K) / (1 - K)
   M = (M - K) / (1 - K)
   Y = (Y - K) / (1 - K)

This was taken from a web-faq on color spaces.  Does anyone know of a more
accurate way of doing this?  Is this in vain?

On another note...does anyone know of a way to convert an RGB value to
it's Pantone equivalent?  Somehow I doubt it, but it's worth a shot.

Thanks for any help..

Bryan Horling

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