RBG to CMYK, Where is my blue??

[gui_999]

I just finished my CP, and I converted it in CMYK, but all the blue turned purple, check

http://membres.lycos.fr/soad999/cp.htm

So, will it turn that what when I'll print it I want it blue, not purple

[Larry Smith]

Well since no one else seems to be taking this one I quess I'll try.
First off let me say great work; it looks awsome!
There are lots of possible reasons and lots of possible solutions depending on the circumstances.
First the possible reasons:
There is no universally accepted way of converting RGB to CMYK and different programs do it differently. Also there are also certain shades of blue (red also) that can be produced in RGB that cannot be produced in CMYK (CMYK is a smaller 'color space' than RGB) the shade(s) of blue that are most likely to give trouble are royal or cobalt blue. I think this is part of your problem. Finally it's possible that conversion fron CMYK back to RGB for display on the monitor is the problem or part of it and the printed piece will be closer to the original than on screen although this one is less likely.
Here are some possible solutions:
Do the conversion to CMYK in a different program or let the printer do the conversion.
If I had to guess I would say you used photoshop to convert this, photoshop is a great program but it like to make unreproducable shades of blue overly purple.
Which brings us to the next possibility, use photoshop or another program to adjust the color more to your liking. Even if the tones you want aren't exactly possible you can probably come a little closer by removing some of the magenta. The only way to know for sure what somthing will look like is to print it, so if budget and time permits do a small test sheet with shades in the range you want and see what they look like.
Finally, no one likes to here this, but in the end the best solution is to learn to like the final result. Even a little purple your panel will look great.

[PoDunkMoFo]

Simple solution....don't convert it to cmyk.

Basicaly the other post has the idea.  The human eye can see a huge range of color, your monitor can display a smaller amount of the range you can see, and a cmyk printer can print an even smaller range than your monitor can display.  We won't even go into the fact that monitors and printers use different methods to create colors (sorry I said I wouldn't go into it).

If you are having your printing done on an inkjet printer I wouldn't convert it.  The reason is that an inkjet can actually produce more colors then offset cmyk printing which is what cmyk conversion in photoshop is based on.  By converting to cmyk you may be tossing out colors that are achievable on an inkjet.  If you have your printing done by someone with an 8 color printer you will lose even less of your colors.

Whenever I print to my printer even when I was working with a 4 color printer I did not convert to cmyk.  I always send my files as they were created if possible.

Hope this helps.

[Frostillicus]

Basicaly the other post has the idea.  The human eye can see a huge range of color, your monitor can display a smaller amount of the range you can see, and a cmyk printer can print an even smaller range than your monitor can display.  We won't even go into the fact that monitors and printers use different methods to create colors (sorry I said I wouldn't go into it).

Actually the human eye can only see about 10,000,00 colors (only!) and the computer, at the standard 24 bit color depth can display 16.8million colors.  Your statement is true if you set the color depth to 8 or 16 bit.

Anyways to the original poster:
The sole reason colors don't look the same on the screen as on the printer is because they are produced in two entirely different ways.  The method on the monitor is called additive, because light is added to each part of a pixel to achieve white, where as color is subtracted in printing to achieve white - that's called subtractive.  A good example of additive method are the strobe lights at a night club - when 2 different lights combine on the floor the result is a brighter, whiter spot than either one alone.  Subtractive is the same as coloring with magic markers - each stroke of whatever color over another results in a darker image.  

Cyan Magenta Yellow and blacK are the least number of colors with the correct hues to produce the widest range of other colors.  But you'll never see a good blue or red without an 8-color printer like the one mentioned above, and even then it won't look as good as on the monitor.

What you've hit on is the biggest crux of the digitial imaging community - Color Management.   It's a huge issue.  
But that was good advice by Larry - either scale back the red in your panel or learn to like purple

[gui_999]

So I thing I'll bring a 300dpi version of both the RBG and the CMYK.

I've put the CMYK more to my taste, take a look

http://membres.lycos.fr/soad999/cp.htm

So I'll bring the 2 to the printing store and talk with the guy which one will come out the best. I hope I can have some blue  

[neuromancer]

Basicaly the other post has the idea.  The human eye can see a huge range of color, your monitor can display a smaller amount of the range you can see, and a cmyk printer can print an even smaller range than your monitor can display.  We won't even go into the fact that monitors and printers use different methods to create colors (sorry I said I wouldn't go into it).

Actually the human eye can only see about 10,000,00 colors (only!) and the computer, at the standard 24 bit color depth can display 16.8million colors.  Your statement is true if you set the color depth to 8 or 16 bit.

Irrespective of bit depth, there are many colors the eye can see that cannot be produced on a monitor. There are also colors the monitor can make that the printer cannot, and colors the printer can make which the monitor cannot.

With 24 bit color, there are only 256 shades of neutral grey. The eye can distinguish many more shades than 256, especially in a smooth gradiation. You can see this to spectacular effect in photos of sunsets, where there are pink and orange bands of color.

My guess is that such a radical shift in colors is likely due to a color profile being mixed up or improperly specified.

Bob

[RandyT]

... and colors the printer can make which the monitor cannot.

This I have trouble agreeing with.  Typically, a printer has a much smaller color gamut than a monitor.  This gets better with more inks, dye sublimation and high resolution, but the monitor is still the more capable device  (we're talking a good monitor, not the $79 special ).

My guess is that such a radical shift in colors is likely due to a color profile being mixed up or improperly specified.

Maybe, but there are definitely hard limits on what colors can be reproduced based on a number of variables.  

1) The cast of the paper.
2) The gamut of the CMYK inks being used (they aren't all the same)
3) The dot density/gain/bleed
4) The abilities of the driver and/or RIP
5) etc.....

PDMF:  All files sent to a 4-color printer are sent in CMYK format.  If you have a properly calibrated setup, conversion of an image to CMYK should get you a close idea as what to expect from the printer because it will use the gamut of the inks and only show what can be produced.

When you send an RGB image to a printer, the driver or RIP will do it's best to convert that information to CMYK.  If the driver or RIP is improperly calibrated the results will be poor.  But RGB or CMYK, the gamut of the inks is always the limiting factor, even on the best of setups.

RandyT

[gui_999]

So should I put the 2 version of my CP on a single 8"X11" and do a print test, then compare?

[RandyT]

So should I put the 2 version of my CP on a single 8"X11" and do a print test, then compare?

If you go to a normal printing shop (not a franchise) you can usually take along a sample of what you want the print to look like.  What they will do is load your file (and in this case, an RGB file is preferable) and tweak it to look like your print.  

Since they will most likely have a well calibrated system, what they see on the monitor is usually pretty close to what comes out of the printer.  So they can visually adjust the image on-screen to get it close to the sample print you provide.

Some places don't want to be bothered with this kind of stuff, but the smaller outfits are usually pretty good at trying to accommodate.

RandyT