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rgb vs cmyk

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  #11  
Old 10-12-2005, 03:10 PM
ydelle's Avatar
ydelle ydelle is offline
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If I know it is for print I start with CMYK. if it is for the epson 9600 I work in rgb.
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  #12  
Old 01-08-2007, 09:55 AM
praveenbr praveenbr is offline
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Re: rgb vs cmyk

If i have a jpeg, how can i identify if it is a RGB or CMYK? Is there any tool available which determines it?
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  #13  
Old 01-08-2007, 07:29 PM
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Re: rgb vs cmyk

Typically a JPEG that comes from a camera is sRGB or RGB. It's just what most pro-sumer cameras default to.

I do prepress work and always work in RGB and save my work as a Photoshop RGB file. I will then convert to CMYK as the final step and send a CMYK TIF file out for print. If doing my own page layout, I just drop the PSD file into InDesign and set the print options to convert all RGB to spot when it goes to RIP (or I will set that option when preflighting for an InDesign package). I soft proof on an Epson 900N or Epson 2200 and get very good results.

As far as letting Photoshop handle the RGB->CMYK conversion, it may depend on the graphic. If it has a lot of out of gamut areas, I'll do some of the adjustment myself with HSL and curves/levels. If the out of gamut areas are not prominent or in non "essential" areas of the graphic, I just let PS do the conversion. Either way, those "hot" (out of gamut) areas are going to get converted. It's just the nature of 4 color process printing.

For a simple explanation of color conversion see my video tutorial in the RTP tutorials forum.
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  #14  
Old 01-09-2007, 01:05 PM
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Craig Walters Craig Walters is offline
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Re: rgb vs cmyk

praveenbr, welcome to RP.

most graphic editors will have some sort of identifying tool. in paint shop pro it's called 'info'. in photoshop, i'm not sure, but i'm sure it's there somewhere. these will tell you all sorts of information about the image, like image size, image type, what color space it's in and so on. if you're using photoshop, i'm sure you can find it or someone can direct you to it.

you could also use something like irfanview as well. even windows explorer will give you some info if you hit 'properties' on the image.
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  #15  
Old 02-17-2007, 04:23 AM
Andrei Doubrovs Andrei Doubrovs is offline
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Re: rgb vs cmyk

Why not see what does the Photoshop Help Center say?
Just one quotation from "Correcting in CMYK and RGB" page:

If you must convert your image from one mode to another, it makes sense to perform most of your tonal and color corrections in RGB mode and use CMYK mode for fine-tuning. Advantages of working in RGB mode include the following:

- You can save memory and improve performance because you are working with fewer channels.

- The range of colors in RGB spaces is much larger than the range in CMYK spaces, and more colors are likely to be preserved after adjustments.
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  #16  
Old 09-01-2008, 08:38 AM
vengab vengab is offline
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Re: rgb vs cmyk

Hi all,

I have an Epson RGB printer and the option of downloading say a 1.53MB RGB file or the same image in CMYK is 4.28MB

Is the reason the CMYK file is bigger (file size not dimensions) because it is 32 bit as opposed to the 24 bit RGB?

I want the highest quality image for printing so am I better off just getting the RGB file or the CMYK and then converting it to RGB?
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  #17  
Old 09-01-2008, 11:38 AM
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Doug Nelson Doug Nelson is offline
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Re: rgb vs cmyk

CMYK has one more channel than RGB, so will be larger.

Sending a CMYK file to an Epson printer requires the driver to convert it to RGB, so better to convert it to RGB yourself.
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  #18  
Old 09-01-2008, 12:27 PM
vengab vengab is offline
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Re: rgb vs cmyk

Thanks for the reply Doug but do you think the considerably smaller file size RGB option of the same image that I have access to would be sufficient, or should I go to the trouble of downloading the CMYK and then converting it?

Download and print would by far be easier but would I be sacrificing quality?
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  #19  
Old 09-01-2008, 04:05 PM
Doug Nelson's Avatar
Doug Nelson Doug Nelson is offline
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Re: rgb vs cmyk

One extra channel would not explain that size difference. The CMYK file is obviously a higher-resolution file. However, on an inkjet you really won't see much difference after about 200ppi.

Even 4MB for a file destined for print is tiny. If there's not a lot of blue in the image, try the CMYK (blue is the weakest link). Download them both and compare the resolutions.

In answer to your original question, 32bit would not enter into it, that's a different thing than when we discuss 8 and 16bit files. All 32bit images are RGB (at least in Photoshop).
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