Method to convert to CMYK??

[MarkC-UK]

Afternoon all.

I've designed a roller banner for a mate but used Corel Paint Shop. Basically there are a couple of images, a floorplan, an exterior render and some text. I can save out the finished image as jpg/tiff etc etc and all is well.

However, the company supplying the banner state:

Our wide format ink-jet printers all use CMYK colour to output. If your design work includes Pantones, RGB colours or Duotones we strongly recommend converting these colours to CMYK for optimum results and colour matching.

Our wide format ink-jet printers all use CMYK colour to output. If your design work includes Pantones, RGB colours or Duotones we strongly recommend converting these colours to CMYK for optimum results and colour matching.

Paint Shop Pro can print CMYK seperations to hard copy but I can't see any way that I can output an electronic CMYK file??

Any pointers??

Thanks:)

[BrianKitts]

check your help file and find out how to convert your document to CMYK. Do not just try to export a cmyk. You will need to work in cmyk colors to see your final color quality.... if not when you get your final print you probably be unhappy, yelling at the printer and they will tell you "they warned you"

 

Professional printing in cmyk can not produce many of the colors that an RGB print can output. Illustrating this point....I threw together a grid of colors in photoshop duplicated the file, then converted one to cmyk. See the attached screen shot of one ontop of the other. You will notice the colors aren't as vibrant in the top (cmyk) version.

[Ernest Burden III]

Our wide format ink-jet printers all use CMYK colour to output. If your design work includes Pantones, RGB colours or Duotones we strongly recommend converting these colours to CMYK for optimum results and colour matching.

 

OK. But what machine is it? Many of the large format printers use RGB drivers, even though the inks are indeed CMYK. Feeding them a CMYK file is a double conversion guarenteed to get the worst results. Ask the output company for a CMYK profile for their device. OR, at the very least, ask them which CMYK space is right for their device.

 

You see, when you tell Photoshop to convert to CMYK it biases the file to the current CMYK workspace. So if you have a default install that will be SWOP2, which mean Standard Web Offset Press. A printing press, not an inkjet output. The change is not reversible.

 

Considering that you are working for free, I suggest sending the RGB file in TIFF format and ask that the output house do the conversion. It takes a minute or less. And depending on which output printers they use, may even be a step backwards. Play dumb, say you don't know the right CMYK space, so didn't want to bung up the file. Then run away as fast as you can.

[Arnold Gallardo]

Nice tips Ernest on the RIP issue. That's something most people do not address

 

When you do convert from RGB to CMYK never ever convert that directly IF you have CIELAB color space to convert to as an intermediate. In Photoshop this would be the LAB color space. Why? CIELAB has a wider gamut for that than the RGB, the indirect conversion would not have a drastic threshold chroma clipping.

 

Always go from RGB-LAB-CMYK.

[Ernest Burden III]

Always go from RGB-LAB-CMYK.

 

Thanks!

[Matt McDonald]

In the process of converting from RGB to CMYK Photoshop's color management engine will convert to LAB anyways. There is no need for you to go through an intermediate unless you intend to perform some kind of color correction for which the LAB space is ideal.

 

Unless the print provider tells you the destination CMYK space there is no point in converting it yourself. Provide them with the large gamut RGB files and they can convert it.

 

All of your RGB images should be tagged with their appropriate RGB ICC profiles.

[Arnold Gallardo]

I don't know I never relied on PS's built-in conversion stuff. Ive had weird colors happen when I directly convert from RGB to CMYK although this always happens with the 'metamers'. I wont take that risk. I used to be a pressman so I try to be careful when it comes to these things. Converting from RGB to cieLAB to CMYK has been very safe for me since I also do pre-press work.

 

It is always a good idea to ask for a 'printer's spec' before you start any job that will go out to press. This would save you time as well as money. You get as much information for the 'end use' before you start any job

 

BTW also don't convert from RGB to Grayscale directly. It is better off to convert to CIELAB first then remove the chroma channels (a and b channels). The 'Lightness' channel has all the luminance data you need. GO test it yourself, RGB to Grayscale will have less contrast and less dynamic range than RGB-LAB-remove a,b channels-Grayscale.

[Matt McDonald]

well being careful is the most important thing. I would never suggest that the conversion to LAB was a bad idea. Personally, I'd like to do away with RGB as a working space. Oh, my how great would it be if studio max supported LAB?... one conversion, right into destination space.

 

I like to use channel mixer to make a grayscale image... it looks more like film.

 

Ah photoshop.

[Arnold Gallardo]

Well for max to support other color spaces would need to rewrite the render engines. Most render engines claim spectral response computations but stores data as RGB crazy! Anyway that would require a render engine rewrite if the color space is change as well as a different kind of tone mapping routines.

[Ernest Burden III]

I like to use channel mixer to make a grayscale image... it looks more like film.

 

Ah photoshop.

 

I do that, too. Remember to work in 16bit mode, too. Grayscale 8bit is a GIF without color.

[MarkC-UK]

Crikey. Thanks for all the replies and especially the example colour grid.

I spoke to the print house and they said they will carry out the RGB to CMYK conversion for me. He also said he will send back the converted file for me to check before printing the banner.

Thanks all:D