Hi,
I am sending artwork to be printed on a large-format composite printer. The design emanates from a website background and is therefore in RGB. But that shouldn't be a problem should it? I mean it would be just the same as sending a photo to a composite printer and you never convert to CMYK in those cases.
Anyway, to get the brightest colors/largest color space I have assigned and converted the document to AdobeRGB, but now I wonder: should it suffice to mention to the service bureau that the PDF is in AdobeRGB?
I mean if I convert to CMYK I might get duller colors than possible. If I retain aRGB color space, it's only their ink and paper that sets the limit. If they only know that the PDF is in aRGB they should use that as an input profile and then use the optimum profile for their output, right?
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One other thing I am curious about in connection with this. Why must I embed both RGB and CMYK colour profiles if I want CorelDraw to remember what RGB profile is? I mean it takes 1,75 MB just for the profiles only. If I could embed just the aRGB profile, it would be a lot less, around a few kB I think. And If I want to send it to a composite printer, like above, it wouldn't use the CMYK profile anyway, would it?
I experimented with this some more and I found that if exactly all colors in a drawing are RGB, then no CMYK printer profile will be embedded, only the RGB profile, which is 0,5 kB (aRGB). The difference in my file is form 110 kB with RGB only (aRGB) to 1446 kB with some CMYK objects in the drawing. And the lower number is obtained EVEN if the save dialog says 1,75 MB for embedding the ICC profiles. So, actually there is something wrong with the calculation.
Anyway, my conclusion is that if you keep all CMYK objects away you will get away with a lot smaller file sizes, because only the RGB profile will be embedded, and that is a lot smaller.
I believe you're right; only profiles for RGB will be embedded if there are no CMYK objects in the drawing.Regarding the size (have noticed it too), I guess it's because the file is compressed, including the profiles. Just a guess though.
Well, the file size corresponds to the ICC profiles embedded. aRGB profile is only 560 byte (0,5 kB).
What do you think about my reasoning regarding sending artwork to large-format composite printer? Is RGB better for larger color space or is it equally good sending CMYK?
I've heard people saying that RGB should increase the color space when printing CMYK, but from my own tests I must say the difference is hardly visible (if at all). May very well have something to do with the profiles.
I'm sure David Milisock can give you some info regarding this. I'll send him a message.
Ronny Axelsson said:I've heard people saying that RGB should increase the color space when printing CMYK
Great conversation and thank you for the invitation to join in the dialog.
Ok here is the way it works, and the reason I answer like this is because there is NO STRAIGHT YES OR NO, or yes send RGB or no send CMYK answer. Especially since there is such a wide disparity between the abilities of different graphic technicians, even though the technology is identical amd also the output devices available offer a wide range of output gamut, ranging from the smallest gamut (CMYK web press uncoated) to the widest say on an Epson, HD hex color which is a little bigger then Adobe RGB.
CMYK gamut REGARDLESS OF PRINTING PROCESS is a composite value of the ink set (the hue of the inks) and possible ink density, (media and process related). This is why there are specifications such as SWOP that set controls over the hue of the base inks. Also the need for a media (paper) linearization, ink limit, dot gain curve.
POSTSCRIPT COLOR MANAGED DEVICES
For press processes the rule is ALWAYS WORK IN AND SEND CMYK. Which CMYK is the question? Well in reality the process for printing presses is postscript color management so NO MATTER where you are in the world and NO MATTER where in the world you're sending the CMYK file to printing press, the only governing principle is the TIC (total ink coverage) of the media, linearization, ink limit dot gain curve for the type of work.
So for printing press work send CMYK, a TIC 340 for sheet fed coated, a TIC, 300 for web press coated, a TIC 280 for sheet fed uncoated and a TIC 240 for web press. Standard ECI or SWOP CMYK profiles fit the bill. If you want to test the TIC of your CMYK profile create an Adobe or ECI RGB image with lots of R 0, G 0, B 0 areas in it and convert to the various profiles, read the converted CMYK image with the info docker in Photo-PAINT and set the secondary color to be total ink. I use an RGB test image which has very dark areas and it will when converted to CMYK tell you the TIC of any CMYK profile.
ICC COLOR MANAGED DEVICES
For digital copier print engine devices I recommend that you also send CMYK, the reason for this is that while these devices are most likely capable of accepting and converting RGB the conversions many times not what the user desires. This is because the gamut of these devices while wider then a printing press is not anywhere near sRGB and if you want to use RGB as output then I suggest the output device have a gamut that is near to or exceeds sRGB. Actually the CorelDRAW default of web coated works fine for these devices.
For ink jet printing there are three categories, non-postscript driver based devices, postscript driver based devices and RIP driven devices. There are two sub-categories for RIP devices, RIPS that do not allow the creation of media profiles and those that do allow the creation of media profiles. Now the EXACT SAME PRINTER CAN WORK FOR ALL THESE PROCESSES, they just produce the results that are limited by their interface.
Worst device is the non-postscript driver based device, any version CorelDRAW work in RGB and send RGB and take what you get, attempting to modify profiles will be dubious at best.
Next worst is the postscript driver based device, X4 and older work in CMYK and send CMYK, X5 use any color model you want, attempting to modify profiles will be dubious at best.
A better device is the RIP controlled device that uses pre-configured ICC media profiles. These are canned profiles better then your driver based devices and you can try different profiles for improved performance. X4 and older use any color model you want but USE NATIVE COLOR COREL PUBLISHED PDF ONLY and set the RIP for an assumed color space work flow, (the RGB and CMYK source profiles set in the RIP match Corel) . X5 you can use any color model you want and send PS, EPS or PDF files Corel or Distiller published PDF.
The real question is how good are the people I use for my output? When you know that they it's easier to send the files that will work the easiest and the best.