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Re: [OM] CMYK and RGB

Subject: Re: [OM] CMYK and RGB
From: "C.H.Ling" <ch_photo@xxxxxxxxxxxxx>
Date: Wed, 2 Sep 2009 09:18:13 +0800
Thanks for all on the comment about the CMYK issues. Waynes and Bill, you 
are right about the color cast on this image, I was just concentrated on the 
red taxi, the saturation on the PS file is too low. Checking with other 
images there are no such green cast issue with Irfanview conversion and both 
have similar color, just the PS conversion has less color 
saturation/contrast.

Office hour just started, I think I'd better ask for the company to send 
sRGB files again.

C.H.Ling

----- Original Message ----- 
From: "ws"

>I was reading my PS Lab color book and noticed some comments about
> converting to-from CMYK, and the different interpretations of CMYK. One
> experiment might be to convert to Lab first, then to sRGB. If there are 
> any
> gamut issues between the color spaces, PS and others have to interpret
> the best compromise. It seems that the most likely color shift issues
> occur with darks. To my eye, and calibrated monitor, the photoshop 
> conversion
> you posted has more detail in the dark areas of the image. The InfranView
> version has less and seems to have a greenish color cast.
>
> More likely than not, you will need to color correct the images a bit no 
> matter
> what, since all CMYK is open to printer interpretation. I would
> go for the PS version with more dark detail and fix that one.
>
> Remember, any out of gamut colors are going to receive interpretation
> when converting to/from CMYK. Since this image has a lot of very bright 
> and
> very dark areas, the CMYK is not going to be a good space for it. Very
> bright and dark colors are hard to represent accurately.
>
> Another option is to load the image into ACR first and adjust, although
> I have never done so with CMYK.
>
> WayneS
>
> At 01:14 PM 9/1/2009, you wrote:
>>Unfortunately I found very big difference between different softwares and
>>I don't think PS did a good job:
>>
>>By PS:
>>
>>http://www.accura.com.hk/temp/24_1_PS.jpg
>>
>>
>>By InfanView:
>>
>>http://www.accura.com.hk/temp/24_1_IV.jpg
>>
>>I also tried to convert a digital camera image from sRGB to CMYK, the 
>>color
>>changed a lot with the "Convert to Profile" setting:
>>
>>Source: sRGB
>>Destination: Working CMYK - U.S. Web Coated (SWOP) v2
>>Engine: Adobe (ACE)
>>Intent: Relative Colorimetric
>>Black point Compenstaion
>>Use Dither
>>
>>I save the converted file to CMYK tiff and then import back to PS, use the
>>same procedure to convert the file back to sRGB but the color didn't 
>>change.
>>That means it is very differ from the original sRGB camera image. I'm
>>confused?
>>
>>C.H.Ling
>>
>>
>>
>>----- Original Message ----- 
>>From: "Sue Pearce"
>>
>>>I work with CMYK files all the time, as that is required for printed
>>>pieces.
>>> You can simply change the file in PS under mode.
>>>
>>> There will probably be some differences in the two files, but it 
>>> shouldn't
>>> be very noticable.
>>>
>>> Bill Pearce
>>> ----- Original Message ----- 
>>> From: "C.H.Ling" <ch_photo@xxxxxxxxxxxxx>
>>> To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
>>> Sent: Tuesday, September 01, 2009 10:27 AM
>>> Subject: [OM] CMYK and RGB
>>>
>>>
>>>> Just got some CMYK (TIF) files from a customer but what I need is RGB 
>>>> for
>>>> slide output. Is there anyone know to properly load CMYK file? I got 
>>>> very
>>>> different results by using Photoshop and IrfanView, IrfanView gives 
>>>> much
>>>> more closer color than Photoshop. The CMYK files just look ugly when
>>>> loaded
>>>> to Photoshop.
>>>>
>>>> Thanks in advance for your help!
>>>>
>>>> C.H.Ling
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