Kosas asks: >Greetings all! hiya Kostas :) >Well the title says it all, I have trouble converting RGb to CMYk many people do! >Actually I am preparinga poster for my niece and it has Magenta, Yellow, Blue and Green colors as a rainbow style background. >I prepared it in aRGB and when I converted it (through Lab or not) the colors were all wrong. If you want something to output in CMYK, it's definately best to start in a CMYK palette that is matched (calibrated) to the printer, this is of course difficult with photos included - something the graphic designers had to wrestle with and now us photographers too >I even redid it in CMYK taking the exact values from the colors palette and the result is the same. >(the best results were obtained by adding white gradients and tinkering the hue/saturation. did not work for the Magenta though) by best do you mean onscreen? Unless the system is totally calibrated then what you see will not represent what you'll get and the colours could be right for the printer, just not right on the screen. what about printed, how does that look? What printer are you printing from? >My settings are aRGB1998, Euroscale coated CMYK, and my Screen profiles in aRGB1998 (no CMYK profile available) >Now is that a monitor issue (cannot show the CMYK colors correctly) so still the colors will print correctly, or is there a setting that will let me get pure magenta etc? your screen can never really show CMYK (usually viewed as reflected colours) as it is an RGB, light emitting monitor. Dont trust the monitor.. you'll need to this by working backwards from the print. this is the really complicated part of printing. A few things to consider: If you have a true CMYK (4 colour) printer then it is best to obtain a profile for it and work withing the profile. * if you have a 4 colour printer without a profile, create 4 patches and fill them just with c, m, y and k and print it - what you get will be the best colours you'll get from that printer and will be as 'true' as it can do If you dont have a profile of can't get one, you would be best working backwards from the printer , getting the best out of it you can and working backwards through your workflow to achieve a degree of calibration. If you dont have a system calibrated to that printer and the colours you got (above) look OK , trust that the colours will be correct at the printing stage and ignore what your monitor looks like If you want a certain colour, make the colour up with the palette - if you think it's wrong, download 'Colorcop' http://colorcop.net/ it's a 60kb color picker - good for checking colours and giving them to you in hex or RGB values - so if you DO want to work in RGB you can create the colour you want for a CMYK profile and find the RGB values of that color, or, you can find a CMYK colour somewhere and discover the RGB values of that colour. If you dont have a 4 colour printer and you're working with a 6 or more ink Photoprinter then forget woring in CMYK - you dont have a cmyk printer! you actually have a cPcmPmyk printer or maybe a cPcmPmyRGK printer :) Best to work in RGB and let the printer RIP do the colour conversion for you - these days they do a really good job! (and there's nowhere you can set absolute ink colours in these photo printers anyway - ie, you can't say 'print 0,0,14,12,34,0,0,3' ) To test that, create the 4 patches again c, m, y and k and fill them with the appropriate values in RGB (so #00FFFF in hex, or 0,255,255 in RGB) then print it from a program other than photroshop, or turn off ALL colour management before printing - see what that looks like - these colours will represent the printer palette, the gamut, and will be the best the printer can do.. If you're using a Canon printer set it to high quality or photo, an Epson set it to high dpi.. If you have colour management turned on you are asking photoshop to interpret your colours and work to a restricted gamut or one broader than your printer can do. Also for all your print tests be aware that the media type effects the ONLY the amount of ink being sprayed out by the printer on Canons and HP's and others, while with Epsons it also effects the colours being produced, because Epsons for some weird reason have set their printers up to be utterly profile dependant (so unnecessary, so excessively complicated, but a good moneyspinner for the ICC mob!). If you pay into the ICC and have all their gadgets, Epsons are fine - if you just want a printer to do what it's told without having to buy or create specific profiles for every piece of paper you hold near it, other brands are better. Colour management changes regulary - 3Dap, bvdm, fogra, ugra, pass2pass, gracol, swop, g7 - seriously.. every year we're promised a 'new, exciting and more accurate approach to color management' - every year people switch and swap about trying to get color under control, every year the users sigh and wait for the next version to do what was promised - fact is, with 4 colour printers, a profile mapped to a SINGLE CRT monitor, ONE batch of dyes, mixed and loaded to the printers all at once by ONE person.. you *may* get consistency - anything else depends on luck or the very accurate eye of a veteran print operator. The colour management system we photographers have inherrited from the graphic guys is complicated :/ Try outputting the patches above - or creat a big page of those patches (cmyk), repeat them down the page and apply a gradient across them by the numbers! ie in CMYK 255,0,0,0 0,255,0,0 0,0,255,0 215,0,0,0 0,215,0,0 0,0,215,0 200,0,0,0 0,200,0,0 0,0,200,0 175,0,0,0 0,175,0,0 0,0,175,0 150,0,0,0 0,150,0,0 0,0,150,0 or RGB though - it sounds like you're looking for something that looks good, rather than something that is accurate ? have a look here; http://www.hypermedic.com/colors/colortable.htm horrible colours those cmyks ;) Is this of any help? karl
