Colors translating

Colors translating

Post by Jean-Marc RIGAD » Fri, 25 Sep 1998 04:00:00



Hi,

I want to translate one picture file from 3 colors mode (RGB) to 4 colors
mode (CMYB). But if i do that i've all marines blue turn in brown.
Why ?

Thank you for your help.
--
Jean-Marc RIGADE

Rennes (France)

 
 
 

Colors translating

Post by Bill Oliv » Fri, 25 Sep 1998 04:00:00




>Hi,

>I want to translate one picture file from 3 colors mode (RGB) to 4 colors
>mode (CMYB). But if i do that i've all marines blue turn in brown.
>Why ?

>Thank you for your help.

Since you posted this to the AVS and AVS/Express applications
groups, I assume that you are doing this within that framework.
Which of these applications are you using?  Are you using a
commercial module or one of your own?  In Express the most
trivial, yet non-obvious problem I had in writing modules
for display was to correctly set the Image_id parameter.

Also, remember that in order to display using the standard
viewwers in AVS, you have to end up in RGB or RGBA space.  Thus,
even if you do your manipulations in CMYK, you have to get
back to RGBA.

billo

 
 
 

Colors translating

Post by Keith Grave » Wed, 30 Sep 1998 04:00:00


The difference between RGB and CMYK is:

RGB is based on colors which can be created/represented using a light source
such as a TV or your monitor.

CMYK is based on colors which can be created/represented using four color
process printing or ink on paper.

Some colors which can be created with the RGB method cannot be created with
CMYK and vice versa.

When you convert from RGB to CMYK, the Green and Red bits of your color seem
to be translating OK (resulting in brown).
However the Blue part of your color is 'out of gamut' and cannot be produced
using ink on paper.

Sounds like your software isn't doing a very good job of finding a close
match.

If the intention is to send the final artwork to print the only suggestion I
can make is to create an acceptable marine blue in CMYK mode.  You won't get
an exact match for your RGB color but you may get close.
Also, you'll need to test print your CMYK color if you want the closest
possible match.  Try as it may, your monitor can only produce an RGB
representation of a CMYK color.  What you see may not be what you get.

 
 
 

Colors translating

Post by Stephen Jone » Sat, 10 Oct 1998 04:00:00



> Hi,

> I want to translate one picture file from 3 colors mode (RGB) to 4 colors
> mode (CMYB). But if i do that i've all marines blue turn in brown.
> Why ?

> Thank you for your help.
> --
> Jean-Marc RIGADE

> Rennes (France)

There's a fantastic paper in SigGraph '98 exacly about printing process
ink selections for accurate colour representation. It highlights the
issues of not being able to accurately convert RGB to CMYB and suggests
using alternative ink colours matched to the colours in the source
image. Have a read!

Stephen Jones
-------------------
Licom Systems, Ltd.

 
 
 

1. Colors translating

Hi,

I want to translate one picture file from 3 colors mode (RGB) to 4 colors
mode (CMYB). But if i do that i've all marines blue turn in brown.
Why ?

Thank you for your help.
--
Jean-Marc RIGADE

Rennes (France)

2. 3D reconstraction from a stack of 2 D images

3. Help blending two different textures

4. Needed : List of top schools in Visualization

5. MAX R2.5 and Char. Studio R2

6. Is there a geometer in the house? (OpenGL Translate vs POVray Translate)

7. Translating between pdf and MS Word and Publisher

8. DXF <-> OpenInventor translate code

9. S: tool to translate RGB values