How does PDF convert CMYK to RGB?

Hi
I want to know the formula that PDF uses to convert DeviceCMYK to DeviceRGB values. It seems that Photoshop and PDF uses the same forula, where the other Programs use the "normal" formula, which can be found on the internet and some online RGB to CMYK calculators.
Where can I get this formula?

As recommended in the PDF Standard (ISO 32000), all color conversion is done using ICC-based color conversion. The "red book" algorithms are clearly marked as deprecated in ISO 32000-1.

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How do you Convert CMYK to RGB

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When I select all of the objects and choose RGB under Document Color Mode, I still see CMYK plates when I preflight the PDF. Depending on what the Document Color Mode is set on, I either have Convert to RGB grayed out or always available. The resulting file show up as CMYK in both Quark and ID along with CMYK plates when I preflight the PDF.
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First, there's no such ting as "RGB" to convert to, only specific RGB color spaces such as sRGB, Adobe RGB or ProPhoto. You get different values in all of them.
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Hi,
I have a CMYK colorspace in indesign, i want to convert that as RGB color space, I got some codes, but I am getting incorrect data.
Some of the codes which I tried are given below
        double cyan = 35.0;
        double magenta = 29.0;
        double yellow = 0.0;
        double black = 16.0;
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            l_res[2] = l_black * ((float)1.0 - p_colorvalue[2]);
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The values are C=35, M = 29, Y = 0, K = 16 in CMYK color space and the correct RGB values are R = 142, G = 148, B = 186.
In adobe indesign, using swatches we can change the mode to CMYK or to RGB.
But I want to do that programmatically, Can I get any algorithm to convert CMYK to RGB which will give the correct RGB values.
And one more question, if the alpha value for RGB is 1 then what will be the alpha value for CMYK?
Can anyone help me to solve these issues... Thanks in advance.

All you have to do is loop thru the swatches and change the space to RGB. Below is an AppleScript, but it shouldn't be too difficult to come up with the equivalent JavaScript. Your document's assigned RGB space will determine what RGB space the CMYK converts to, so if you are looking for sRGB, then Edit>Assign Profiles...>Assign Profile: sRGB
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repeat with a from 1 to count of every swatch
try
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end try
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Good morning,
I have a question about converting color spaces using Acrobat 7 Professional and Pitstop Pro.
I have some CMYK PDFs used for magazine printing that I need to convert to a 144 DPI RGB version for a digital edition.
I know most folks are concerned with RGB to CMYK but I need to do it in reverse...
If I do a Convert Color in Acrobat CMYK to RGB it looks a lot better than if I do it using an Action List command to Convert to RGB in Pitstop.
The Pitstop ones look almost posterized, way darker with significant color shifts
I would have thought Pitstop would use the Acrobat color engine to do the transformation to RGB but it seeems it knid of does it's own thing.
I do have sRGB selected in my Color Management Prefs in Acrobat.
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I recently used Adobe Color CC to create a color theme that will be used for both print and web. I created the theme with approved CMYK values with the intent of saving the .ASE file to be imported into other CC apps. Corresponding RGB, Hex, Lab and HSB values are automatically created. Of course, we are using CMYK for print and RGB for web
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I found what change it to normal way, but logicaly it's should not be a reason for autoconvert colors. If I choose CMYK and want add CMYK color it should be CMYK (in name minimum) and not RGB.
File->Documents Colors->CMYK(should be, but RGB was)
Right now options open like CMYK, not HSB. But if I want color in RGB it added like CMYK. Options like in CMYK, not HSB, again. Still look like error.

Why don't Adobe Color CC and InDesign CC convert CMYK to RGB the same?

I recently used Adobe Color CC to create a color theme that will be used for both print and web. I created the theme with approved CMYK values with the intent of saving the .ASE file to be imported into other CC apps. Corresponding RGB, Hex, Lab and HSB values are automatically created. Of course, we are using CMYK for print and RGB for web
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It's working for me (Web, PS, AE, ID, FL; not available in the Color Themes panel in Ai). Please click the triangle next to the color space to expand and view more data.

Cannot completely convert PDF from CMYK to RGB

I have a 48-page CMYK pdf that was produced by Quark. All placed images are CMYK.
Using Acrobat X, I select Tools -> Convert Colors -> Convert Colors to Output Intent sRGB IEC61966-2.1, I am able to convert 99.99% of the document to RGB. However, a tiny portion of the document (a total of only 32 pixels) stubbornly remains CMYK. I cannot get a completely RGB PDF, and it's causing problems with our production process.
The parts that remain CMYK are miniscule. For example, there's an apostrophe on page 34, the top half of a comma on page 8. Examination of the uncompressed PDF reveals 3 tiny CMYK objects. Here's a typical object that is only 3x6 pixels.
5606 0 obj
<<
/ColorSpace /DeviceCMYK
/Subtype /Image
/Length 6
/Width 3
/Type /XObject
/BitsPerComponent 1
/Height 3
>>
stream
^Q^P^Q^P^Q^P
endstream
endobj
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3307 0 obj [/Separation /All /DeviceCMYK 4249 0 R]
endobj
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on page 45
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(2) Image 935 (out of 2432)
on page 48
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Width/Height (pixel): 3/3
Bits per color component: 1
Treated as a mask: False
Perform interpolation: False
Compression/encoding
ZIP/Flate compression (FlateDecode)
DeviceCMYK color space
(3) Image 2233 (out of 2432)
on page 34
Image properties:
Page 34: CMYK
Width/Height (pixel): 2/5
Bits per color component: 1
Treated as a mask: False
Perform interpolation: False
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ZIP/Flate compression (FlateDecode)
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(4) Image 2302 (out of 2432)
on page 8
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Page 8: CMYK
Width/Height (pixel): 2/7
Bits per color component: 1
Treated as a mask: False
Perform interpolation: False
Compression/encoding
ZIP/Flate compression (FlateDecode)
Why can I not complete the CMYK->RGB conversion? And why do only 32 pixels out of millions in the document refuse to convert?
Is there a way to force the document colorspace and all colors to become RGB beyond what I've already done?

That might be it, Jacob.
It's when, for instance, I have the Appearance window open and shift-click on the stroke or fill to see the color attibutes (rather than simply looking at the swatches). It kept showing up in CMYK.
But making that change in the flyout seems to have it showing properly.
Thanks!

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And,
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I'm wide open to suggestions for best practices regarding artwork for use in MS Office applications.
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Message Edited by jpeters on 04-02-2008 12:38 PM

How does PDF convert CMYK to RGB?

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