Conversion rgb in cmyk

Hello everybody,
i use kuler first time - cool tool!
I have a questions about conversion rgb in cmyk.
In Photoshop or Illsutrator i get complete different values
for the same color.
I try to change the color profiles adjustment, but never i
get the same color values
like kuler. For example: in kuler the cmyk color 0/60/100/0
would translate in rgb 255/102/0.
In PS i get 235/136/14 (in depends what profile i used).
Which color conversion engine or profile use kuler? Can i get
the same profile for PS or IL?
Regards, Lars

Hello, kuler color conversions should be consistent with
Illustrator CS3, since kuler is a subset of the Illustrator CS3
Live Color feature. Generally speaking, it's best to create your
kuler theme in the color space you want to use.
More on color management
here.
Hope this helps!
Sami

Similar Messages

Script for color space conversion RGB to CMYK - URGENT Help Wanted

Excuse my ignorance with the basic nature of this question, I don't use InDesign, but I do have a pressing problem regarding it.
My book publisher has just emailed to say that my photography book has been set for the printers in InDesign and the photographs have AdobeRGB color space (which was what I was aksed to send.) The printer needs the images to be in CMYK. The publisher said that he was "pretty sure Adobe Acrobat converts the InDesign files to CMYK" and that he has sent the printer RGB images in the past and they "came out OK". He said that if this will not work, he needs to convert all of the images separately to CMYK.
Can you help with the following:
1. Is he right about the above - can Adobe Acrobat convert the files?
2. Can anyone offer me a script that will convert all of the images in InDesign to CMYK? or will he need to change them individually?
Thanks for any suggestions with this urgent request.
Stephen

1. Acrobat can convert.
2. No need for a script, if the printer needs CMYK, you can export a CMYK pdf.
3. To get the highest quality conversions, you might want to do it in Photoshop.
4. If the images are color managed and the printer has a modern work-flow a color managed RGB PDFX-4 pdf is probably the best way to go...
Harbs

Conversion formulas from RGB to CMYK

Hi,
I've been writing a Colour swatch tool (in excel! hell yeah!) which allows me to pick a bunch of colours, generate complimentary colours from them, blend between 2 colours in a set number of steps and a whole bunch of other cool stuff, and then output this as a photoshop or illustrator swatch file.
As part of this tool I want to be able to covert the rgb values to cmyk. There is very little information on this on the web and what there is is fairly inaccurate.
For example,
RGB:50,128,128
Converts to CMYK 61,0,0,50 (%) using the formula found at easyrgb.com (this formula is the most prevalent one on the web/web forums)
Photoshop converts these RGB values as CMYK: 80,33,48,8 (%)
While these two colour values are *similar* the ones generated by the easyrgb formulas are nowhere near the photoshop values.
See? stupid useless formulas. (I am aware of the differences and overlap of the two gamuts)
Whilst I know that the conversion done in photoshop is done using ICC templates, and that often these conversions are device dependant, there must be a more realiable way of converting from one colour space to another using good old reliable cold hard maths.
Does anyone know what that might be? you guys at Adobe: I AM LOOKING AT YOU.
Hope you guys can help,
~silvery~
For reference I have included and commented the easyrgb formulas:
First: RGB -> CMY
C = 1 - ( R / 255 )
M = 1 - ( G / 255 )
Y = 1 - ( B / 255 )
Second: CMY -> CMYK
var_K = 1
Initally sets var_K as 1, although this is dependant on variables below
if ( C < var_K )   var_K = C
if ( M < var_K )   var_K = M
if ( Y < var_K )   var_K = Y
This bit finds the smallest value from the CMY range and sets this value as var_K
if ( var_K == 1 ) { //Black
    C = 0
    M = 0
    Y = 0
If var_K (the value that K is calculated from) is 1, then all the CMY values are reset to 0
else {
    C = ( C - var_K ) / ( 1 - var_K )
    M = ( M - var_K ) / ( 1 - var_K )
    Y = ( Y - var_K ) / ( 1 - var_K )
If the value of var_K is anything other than 1 then use the smallest value from the CMY range
K = var_K
The value of K as filtered out from the conditions above

Oliver,
I'm not sure what you mean by the term 'meta' color profiles, but I'll take a stab at what I "think" you are asking. There are some fairly widely accepted "standards" out there for both RGB and CMYK.
In the RGB world, for example, sRGB, Adobe RGB (and to some extent, ProPhoto RGB) have a fairly wide following. These are all ICC profiles, which nail down the boundaries of the color gamut and the definitions of any tri-stimulus combination of red, green and blue. Basically, they are matrix profiles that establish the positions of the Red, Green and Blue primaries, and these positions define the outer limits, or color gamut, of the color space. sRGB is a relatively small color space, so some viewable and printable colors get clipped (sRGB is the general internet, email standard and is widely assumed for many non-color managed appplications, printers, etc). sRGB can handle a fairly wide range of colors, but does clip some colors in brightly colored originals. It has the advantage of being the most widely adopted standard, plus the steps between colors are very close together. I use sRGB for average images, most people pictures, etc. Adobe RGB spreads the primaries further apart, so it describes a wider color gamut. Because the primaries are further apart, the steps are slightly larger from one color to the next, but marginally so. I use Adobe RGB for most of my brightly colored images that will get clipped in sRGB. Adobe RGB is also generally a good choice for images that will ultimately go to a printing press or inkjet. ProPhoto RGB pushes the primaries WAY apart, so it describes a HUGE color gamut...in fact, many of the colors that can be defined in ProPhoto fall outside human vision, and certainly monitors and printers.Due to the wide spacing of steps in ProPhoto RGB, images should be worked in in 16 bit, otherwide you may see some banding and posterization if large edits are made.
In the CMYK world, certain "standards" have been established, mainly for commercial offset printers (both web and sheetfed presses). By creating a standard, they are trying to establish the ink limit, densities, color gamut, dynamic range, gray balance, etc, of a "generic" sheet of commercial printing paper on the average well-maintained press using standard ISO inks, using good process control, mesurements, etc. By it's nature, this process has to encompass a wide cross section of presses, so it may act as a limitation on what some modern presses are capable of, but that's what standards usually do. If a good printer, with a modern press and great process control decides to sidestep the standard, they can probably extend color gamut, dynamic range, etc, but at the cost of no longer being "standardized". If commercial printers are "truly" trying to meet the standard, they will run tests, take measurements, and adjust their entire workflow so it matches the standard, within acceptable tolerances. Lots of shops "claim" to adhere to SWOP or GRACoL standards, but the majority of them don't. Standards for presses make some sense, because blending CMYK inks together (especially if they use ISO standard inks) on paper usually has a reasonably narrow range that works, though the paper makes a huge difference. (the same cannot be said for inkjets, monitors and many other processes, so they generally do not have standards). So for presses, there are standards for matte and coated papers, web presses, sheetfed presses, newsprint, etc. Each of these standards has its own ICC profile (or a family of profiles) that establishes ink limits, color gamuts, etc.
All ICC profiles have the necessary tags and data to comply with the ICC specification. One of those requirements is a "profile connection space", which is usually L*a*b* or a variant. So, an file on your computer may be tagged as an Adobe RGB file, and if you wish to prepare it for a sheetfed press using glossy stock, you could convert the file to GRACoL2006_Coated1v2.ICC (an industry standard profile for No. 1 coated stock on a sheetfed press). Since both files have the ability to "speak Lab" a translation can be made from one color space to the other. The numbers in the Adobe RGB file will be converted to L*a*b* (the universal translator), and then the L*a*b* numbers will be converted to CMYK, specifically GRACoL2006_Coated1v2.ICC. So, now you have a file in CMYK space with new numbers. It is worth noting that RGB has only three colorants to define colors, but CMYK has four. So, while in RGB there is only one way to define a specific color, in CMYK, there are many possible combinations that can generate many colors. This adds complexity to the equation. The CMY colors are called subtractive primaries, and are opposites of RGB (additive primaries). The "K" (black ink) is added for text, line art, neutrality, extra Dmax, and because the CMY inks are not pure and don't deliver a true black all by themselves. If the inks and paper were perfect, you could theoretically get away with CMY all by themselves, except for registration issues, text, line art, etc. Also, the additional "K" ink can help reduce the total ink limit, save ink, reduce costs, and improve quality.
Sorry for the book. This is not a simple subject, and we have only touched the surface.
Lou

Choosing profiles for forced RGB to CMYK color conversion

When a mixed RGB/CMYK PDF is opened in Illustrator CS6, Illustrator forces a conversion to one color space or the other. See this screenshot: http://imgur.com/sK8iEdn
I assume this is a limitation of Illustrator and there's no way to keep both color spaces. Under that assumption, Is it possible to choose the profiles used for the conversion from RGB to CMYK? Can Illustrator be made to use the RGB and CMYK profiles defined in its Color Settings to make this conversion?

I did some experiments with Illustrator CS6 and the MacBeth RGB test chart and verified my results with Photoshop CS6. I discovered Illustrator is (mostly) doing what it should be doing, within a 1% error (probably rounding) on the output CMYK values. Here's a summary, in case anyone else needs this info:
Assuming the source file's elements are all untagged, when a mixed RGB/CMYK PDF is opened in Illustrator and CMYK mode is
chosen, Illustrator will use the profiles and rendering intent defined in
Color Settings to make the color conversions from RGB to CMYK. Thus, we
have control over the profiles used for this conversion.
If the RGB elements in the PDF file have embedded ICC profiles,
Illustrator will use the embedded ICC profile instead of the RGB profile
defined in Color Settings. This ONLY happens, however, if the PDF file
also includes the correct CMYK output intent profile.
If the PDF doesn't contain a CMYK output intent, Illustrator will fall
back on the Color Settings RGB profile for RGB->CMYK conversion. I believe it
would be more correct for Illustrator to use the embedded RGB profile and
the CMYK profile defined in Color Settings, but that's not how it seems to work.
If the PDF contains the incorrect CMYK output intent, Illustrator will
ignore the Color Settings and respect the embedded RGB and CMYK profiles
for the conversion, as might be expected.

RGB to CMYK conversion issue- Pulling my hair out@

Hi there-
I have downloaded a VECTOR image from Shutterstock, and it was built as an RGB file. When I try to convert it to CMYK (File-->Document Mode-->Concert to CMYK), it totally whacks out the image. I have tried everything I know how to do, and can't figure this out. I've tried changing the colors in the palette to CMYK, but it doesn't convert them permanently.
I'm attaching two files (as JPEGS so you can see the problem), one shows the sunshine image nice and smooth. The other is after the conversion to CMYK.
If you have any ideas, or want to see the actual file, please email me at [email protected] and I will send you the actual .eps file.
THANK YOU!
Brent

Original file above.
Select all
Object> Flatten transparency (check preserve alpha transparency with slider to 100 vector)
Change color settings (edit> color settings) to emulate Illustrator 6.
Convert to cmyk mode
Results
There were two main issues converting to cmyk.
Use of screen blending mode and the gradients themselves.
Screen blending mode was described in previous posts.
The gradients look also changed when converting from rgb to cmyk. If the screen blending mode was switched to normal, when converting to cmyk, the gradients would not look the same.
Flattening transparency is not an elegant solution, but it is a quick and dirty one.
Mario described this method in a previous post.
Depending on your color settings, it may yield unwanted artifact colors. Turning off CM, setting to Illustrator 6 emulation, will not yield the artifacts.

Conversion from RGB to CMYK

Hi,
I would be so grateful if someone could help! I need to submit a PDF of a book I have written to the printers. They tell me that they are printing in CMYK. My book has many paintings inside and two use RGB mode (others are CMYK). I have tried converting these to CMYK however they loose their colour variations and brightness. It is important that the colours remain the same. Is it necessary that I convert these to CMYK (my printer said he would try printing samples of the PDF's I've sent in RGB mode and see what happens). I am worried since when I export the book to PDF I get a big exclamation mark warning me not to proceed since all is not in CMYK. Is this simply a caution or is there any reason for real concern. Help!
Thank you, Rachel

There's no way to tell what the settings are from what you've posted. This is a modification of the [High Quality Print] predefined preset, which DOES NOT convert colors to CMYK, but without going through the panels there's no way to know what was modified.
Whatever settings you end up using, you must look at the "output" panel and check what it says under color. If you are expecting the output to convert RGB to CMYK you must set that field to one of the "Convert to Destination" settings, and under destination you must choose the correct profile for your printer conditions.
Choosing "Convert to Destination" and a profile that doesn't match your document CMYK working space will result in the appearance of colors being preserved, but all of your native CMYK elements, including your black type, will be converted tot he new color space, and more than likely your type will now be a four-color rich black instead of K only, which is a printer's nightmare.
Choosing "Convert to Destination (Preserve Numbers)" will keep the CMYK values for native elements, which will preserve your solid blacks, but will result in some color shifting as the numbers are re-interpreted in the new space. This is roughly equivalent creating a document in one working space, then ASSIGNING a new working space before export.
Peter

I can convert almost things multiple times at the same time including CMYK to RGB (or sRGB), but not RGB to CMYK and not brighten/contrast. How?

I can convert almost things multiple times at the same time including CMYK to RGB (or sRGB), but not RGB to CMYK and not brighten/contrast. How?

If you want a relevant answer you may have to elaborate on what you actually mean. Posting screenshots might help, too.
In any case multiple conversions of an image are not advisable in general.

RGB to CMYK problem

I have just started using Photoshop CS3 amending photos and adding text & graphic for printing. The photos start off in RGB but when I get them printed in CMYK they look dark and terrible! Can anyone offer me guidance on how to handle the transition of photos from RGB to CMYK and how to avoid making them darker/destroying the quality?
Thanks!

Are your source RGB files tagged? Are you sure the profile is correct? What's the output CMYK profile? Is your monitor calibrated and profiled?
If you have a good source profile on the files, and you know the CMYK target profile, you should do the RGB-CMYK conversion in Photoshop yourself, then tweak the colors using softproof. (Make sure you save the CMYK conversions and edits as SEPARATE files - don't save them over your source RGB files!)
The resulting files should reproduce much better on the press. If not, chances are good the printer isn't honoring your embedded profile or is doing another CMYK conversion without telling you.

Rgb to cmyk turns white brown

Hi Guys
In previous versions - changing from RGB to CMYK or vice versa would change the colours slightly but ever since CC when I change one to the other my white
goes brown and there is a yellow tone to the image.
Has anyone else experienced this - it's not slight either see image. I haven't adjusted anything - the original CMYK is on the left and
when I make it RGB - it goes brown.
Has anyone else had this issue?

I'd try a new display profile first. Recalibrate, or if you don't have a calibrator use sRGB (or Adobe RGB if your display is wide gamut).
Everything in Photoshop passes through the display profile. If there's a problem with the profile it can happen that one conversion goes bad but not another.
On Windows a common cause for this is bogus manufacturer profiles pushed through Windows Update. Mac isn't as susceptible to this, but there you have an added complication called ColorSync (which is where the actual profile conversions are done). So if a new profile doesn't fix it, you probably need someone with Mac OS X expertise.

RGB to CMYK (channels) with PixelConduit plugin

As I'm unable to submit a user tip yet, I thought I'd share my solution here for anyone looking to simulate CMYK channels in Motion/FCPX.
PROBLEM
For some reason you want to convert your RGB source clip to extract individual CMYK (Cyan, Mangenta, Yellow, blacK) channels. For example you'd want to simulate the printing process of a book on a printing press.
SOLUTION
Use a free FCPX/Motion 5 plugin caled PixelConduit, a node-based visual effects design system. Install the plugin before launching Motion.
To extract CMYK channels, I used a (linear) RGB to CMYK formula:
Black   = Math.min( 1 - Red, 1 - Green, 1 - Blue )
Cyan    = ( ( 1 - Red )   - Black ) / ( 1 - Black )
Magenta = ( ( 1 - Green ) - Black ) / ( 1 - Black )
Yellow = ( ( 1 - Blue ) - Black ) / ( 1 - Black )
and translated it to PixelConduit's nodes.
Clone your source clip four times. Call the clones 'Cyan', 'Magenta', 'Yellow' and 'Black'. Navigate to Library > Filters > Conduit Effect System, choose Conduit and apply it to each clone layer. In Inspector, click 'Show Conduit Editor' and assemble the following node tree for each layer:
K (black) layer:
C (cyan), M (magenta) and Y (yellow) layers are identical except the first channel selection:
So, for M and Y layers change the 'Separate RGBA' node to output the green and blue channel respectively. You can copy/paste the whole node tree between intances of the filter so you don't have to create everything again from scratch.
You should now have four layers outputting a simulation of C, M, Y and K channel in greyscale. If you'd like to present these channels in colour you'd need to add Colorize filter to each clone layer:
And finally, if you use Multiply Blend Mode for each clone layer group you'll get a pretty close colour composition to the original source clip! By fine-tuning colour values in Colorize filters and/or tone curves in Conduit you could probably get a perfect conversion.
Colour values used in Colorize filter:
Remap White To:
1, 1, 1 (all)
Remap Black To:
0, 0.61, 0.89 (cyan)
1, 0, 0.5 (magenta)
1, 0.95, 0 (yellow)
0, 0, 0 (black)
That's it! Hope it can help anyone :^)

As I'm unable to submit a user tip yet, I thought I'd share my solution here for anyone looking to simulate CMYK channels in Motion/FCPX.
PROBLEM
For some reason you want to convert your RGB source clip to extract individual CMYK (Cyan, Mangenta, Yellow, blacK) channels. For example you'd want to simulate the printing process of a book on a printing press.
SOLUTION
Use a free FCPX/Motion 5 plugin caled PixelConduit, a node-based visual effects design system. Install the plugin before launching Motion.
To extract CMYK channels, I used a (linear) RGB to CMYK formula:
Black   = Math.min( 1 - Red, 1 - Green, 1 - Blue )
Cyan    = ( ( 1 - Red )   - Black ) / ( 1 - Black )
Magenta = ( ( 1 - Green ) - Black ) / ( 1 - Black )
Yellow = ( ( 1 - Blue ) - Black ) / ( 1 - Black )
and translated it to PixelConduit's nodes.
Clone your source clip four times. Call the clones 'Cyan', 'Magenta', 'Yellow' and 'Black'. Navigate to Library > Filters > Conduit Effect System, choose Conduit and apply it to each clone layer. In Inspector, click 'Show Conduit Editor' and assemble the following node tree for each layer:
K (black) layer:
C (cyan), M (magenta) and Y (yellow) layers are identical except the first channel selection:
So, for M and Y layers change the 'Separate RGBA' node to output the green and blue channel respectively. You can copy/paste the whole node tree between intances of the filter so you don't have to create everything again from scratch.
You should now have four layers outputting a simulation of C, M, Y and K channel in greyscale. If you'd like to present these channels in colour you'd need to add Colorize filter to each clone layer:
And finally, if you use Multiply Blend Mode for each clone layer group you'll get a pretty close colour composition to the original source clip! By fine-tuning colour values in Colorize filters and/or tone curves in Conduit you could probably get a perfect conversion.
Colour values used in Colorize filter:
Remap White To:
1, 1, 1 (all)
Remap Black To:
0, 0.61, 0.89 (cyan)
1, 0, 0.5 (magenta)
1, 0.95, 0 (yellow)
0, 0, 0 (black)
That's it! Hope it can help anyone :^)

RGB to CMYK to commercial printer

We are using CS2 InDesign and Photoshop 7 on a PC. I am putting together two
large books. One insert section of the first book has color photos. I have
to prepare these color photos for a printer located in China. They want all
images to be CMYK .tiff.
I have an assortment of about 100 images from various sources around the
world, there are .tif, .jpg. .bmp, and .psd. All of them appear to be RGB.
There are images with: 1) no color profile, 2) sRGB IE60966-2.1, and Adobe
RGB 1998. Do all images need to have the same RGB color profile before
converting to CMYK?
I have been converting all of these to .tif (and using a single dpi/pixel
resolution for
all images).
Do I just select/save as color mode CMYK? Or are there special
settings/profiles I need to know about. Is there anything special for China?
The printer's English is not that clear . I was hoping that someone in this
group would be familiar with RGB to CMYK conversion.
Also, it appears that the final PDF pages (with embedded Tiff images) will
be very large. The first complete book for this project (there are two
books) looks like it will be about 20GB. The second book looks like it could
be 12GB. Both books together equal about 1,000 pages and have about 1,000
images. 90% of the images are grayscale. What are the current technologies
for sending large projects like this to a printer?
Thanks
ps, the Photoshop group suggested that I write to this group.

Tech....
In the conversions, are you referring to conversions of B&W or color images? I'll assume color for the moment.
Assuming your monitor is properly calibrated, and assuming you are viewing your color images on your monitor, your conversions should keep "in gamut" colors the same. You will, however, probably see some loss of dynamic range, color, and saturation as you enter CMYK. If the color and dynamic range of the original is all within the destination CMYK gamut, you should see very little, if any, shift. The sad fact is that CMYK on press has limited dynamic range and color, especially compared to a bright monitor. This is generally true, though CMYK can print some colors that lie outside the typical monitor's gamut.
If you have a brightly colored original in RGB mode, then you should experiment with both perceptual and relative colorimetric rendering to see which one looks best. This is an image by image thing. Relative colorimetric will reproduce all "in gamut colors" as accurately as possible, then will take out of gamut colors and bring them to the closest printable color. This can cause loss of detail and 'piling up of colors' as you near the boundaries of the image's color gamut in the destination CMYK space. Perceptual scales ALL colors and preserves the relationships between colors, which sacrifices color accuracy and saturation, but sometimes looks more natural, especially if there are a LOT of out of gamut colors. Pick whichever ones looks best overall.
Then, once in CMYK, make minor curves adjustments to tweak if for CMYK. Just be careful not to push it too far, especially in the deep shadows, since you may push beyond the ink limit of the press. For example, if you convert to US Web Coated SWOP v2, the ink limits are set at 300 total. If you drastically darken the shadow areas, you could end up with an ink limit of 320, 330, 350, etc. Knowing the ink limit of the press will help you stay within those limits. Final tweaking in CMYK is usually a good thing.
How did you determine that the images were dull with too much magenta? Did you print a proof on a calibrated printer, or is this just your screen display? Or is this from a printed image off the press? I have a well calibrated monitor and accurate custom profiles for my inkjet. If I am sending a job to a press that supposedly prints to US Web Coated SWOP, I can proof that file on my inkjet and get a very good match. We need more information to know exactly what you are doing and how you are assessing your images.
Normally, I do the conversion in Photoshop, using the rendering intent that looks best. Then I tweak the image in CMYK to get it looking its best. I usually have the press profile, but sometimes work with a standard profile if no custom profile is available. I leave the image tagged with my conversion profile. Then, I usually place these images into InDesign, with the profile intact (color management turned on in InDesign). I right click on the placed image to be sure that the profile and rendering intent are set to what I want. Then, I can either supply the InDesign file to the printer, or convert to PDF (leave color unchanged) and make sure that all profiles are included. InDesign should export each image to the PDF properly, along with profile and intent. I have never sent to job to press using Photoshop...only InDesign or Illustrator.
BTW, rendering intent is only used when getting an image from one color space to another, such as a conversion from RGB to CMYK. You do that, choosing the one that looks the best. Once it is in the destination CMYK space, rendering intent is no longer needed, since all the colors and tones have already been remapped into the final space. Rendering intent is just used to help us handle those out of gamut colors.
Hope this helps.
Lou

How can you tell if a PDF is RGB or CMYK?

From the screeshto below I am finding the only way to tell if a PDF I receive is RGB or CMYK, is by the transparency blending space. Are there any other ways?
The drop shadow on the chip is showing cyan, along with the yellow arrow. The original files do not have cyan in these areas. Is this because the PDF is being saved as smallest file size, which converts CMYK to RGB, then in Acrobat we are coverting RGB values back to CMYK, and with those color conversions you cannot proof Smllest file size PDFs for CMYK breakdowns.
What are others using out there in proffing PDFs for color, smallest file size with color conversion set to no? Doing that makes our PDFs about 150% to 200% larger and they often wont fit in email then. Are there any secret ways of proofing a standard smallest file size PDFs for accurate CMYK breakdowns?

In Acrobat Pro 9:
Advanced Menu to Preflight
Upper Right corner of Preflight dialog box click on "Options"
then select "Create Inventory"
deselect everything except colors and click "OK"
it will analyze your document and return with the number of "plates" as well as the names of the plates...

CMYK to RGB to CMYK again...why?

I'll be the first to admit - I am relatively new and inexperienced when it comes to color management.
I am a prepress tech - 6 years now or so. Been in printing for 24 years - was a conventional stripper before that.
Not a complete dummy but I was never exposed to the old ways of electronic prepress -
My question is a "why?"
We have a PDF based workflow running Trueflow.
Because we have an older version of Trueflow that requires specific settings in order to accept PDF files, I have a certain criteria that supplied PDFs must meet.
I don't always get them that way - so I have a preflight routine where I open all PDFs and check them for spots/RGB/Lab color swatches, etc and convert as needed to CMYK. I then flatten them in PitStop extreme and run them through my rip.
We do not have the ability to proof with ripped PDF files - therefore, when a PDF proof is required, I want it to be the print file that will be used to output to plates.
OK - now you have a little background about my methods -
Here is the question.
My client was supplied a CMYK vector PDF ad.
Artist for the client opened ad in photoshop, rasterized it and converted it to RGB, placed it in his Quark document and sent the 16 page PDF file to me
I received it, noted that the file was full of spots and RGB and did a conversion back to CMYK in pitstop
We sent a PDF proof to the client, who approved it (for the record, when we PDF proof, we assume that color is not critical otherwise the client would have asked for a matchprint)
OK - so we print the booklet and client is very unhappy with the color on the back page.
Artist says that we should have let the rip convert the RGB file to CMYK instead of doing it myself - like I trust my rip to do what it should - I don't - it has made a mess of things in the past. I know what condition my files have to be in before they go in the oven. I don't take chances.
My question is, why would he convert it to RGB in the first place? I am completely lost on this one. If I am supplied a CMYK file, what reason is there for converting it to RGB before placing it into the document?
Can anyone explain why this would be necessary?
Thanks in advance!!!! I'm sure there are some gurus out there who can make sense of it in explaining it to me.

From what you describe in the original post, I get the feeling that the wrong question is being asked. In the particular case, there was probably no need at all to convert (or maybe even rasterize) the PDF you supplied. If the client's artist only needed to make minor changes to an existing layout, he or she would obviously have been better off applying those changes to the original layout document (InDesign, QuarkXPress) to conserve editable vector data and the source colours of any pixel images. Only if the original layout document was not available or had been modified colour-wise at a later production stage would I have used a PDF as the basis for editing the ad. Maybe the artist inadvertently made the RGB conversion when rasterizing the PDF? As you supplied the PDF and your company ultimately did the printing as well, I see no reason why the data would have to be converted to RGB and back to CMYK; the artist could have easily left everything as is and just added the modifications. What flavour of PDF did you supply? For your CMYK safe workflow, I guess PDF/X-1a would have been the most appropriate one*. Then the artist could work in the device space as you do or convert any new RGB content to the CMYK space as specified in the PDF/X output intent. I would recommend to communicate who does what before the layout work rather than after printing and running across unpleasant surprises. Redundantly converting colours back and forth without a clear and strict process and colour management is a very bad idea in my opinion, and as you saw, it can yield quite unsatisfactory results. It does take more effort to set things up properly, but in the end it tends to cost less and deliver (far) better results than troubleshooting and re-printing a screwed-up mess.
* If your Trueflow system requires different, non-standard PDF settings, then things get more complicated. Your company's management may want to consider whether the equipment on hand is really up to the tasks it is supposed to perform ...

How to make a script to convert RGB to CMYK as black 100%?

Hi guy
my customer sent me a book (144 pages) for print but all of them are RGB and Tiff, she scan them. there are on the page some texts and pictures. The text are R=30 G=30 B=30.I think if I can make a script I will do it very soon to black 100%, but unfortunately I dont know anything to make script
anybody can help me ?anybody can make it for me ?

We need to know some more information.
1. The book consists of 144 pages, and each page is in fact an RGB image in TIFF format.
    Correct?
    That means, the text is already rasterized, but with low resolution (no more than 300ppi).
    A very bad starting point, in my humble opinion. For offset printing this is not acceptable.
2. Is the printing process offset printing or by digital printing?
Nevertheless we may think about a conversion of these images into CMYK K-only (one plate
per page) .
a) Increase contrast until R=G=B=0 for text.
b) Convert each image into Grayscale, using a so-called Black-Ink-Profile, for instance
    Black-Ink-ISOCoated-v2-eci (can be explained later)
c) Make empty CMYK image, here for ISOCoated-v2-eci, and paste the Grayscale into the
    K-channel. All further handling happens as CMYK file for the process ISOCoated-v2-eci.
    Void plates CMY don't matter.
    Post #12 here:
    Re: Colour shift (from CMYK = 0 0 0 20 to Grayscale K = 22 !)
All this can be done by an action (I hope so...).
Much better would be a new start by InDesign with typographical text (K-only vector instead of raster)
with images in RGB or CMYK, taking into account the intended process.
Note: Photoshop can deliver vector text, if exported as PDF.
Best regards --Gernot Hoffmann

Why does Illustrator automatically change RGB and CMYK values

Hi, I am struggling to understand why Illustrator is changing the values inside the RGB and CMYK boxes. I am also not sure of the exact relationship between these values. Essentially, it appears that if you set the Document Color Mode to RGB, it leaves the RGB values that you type in alone. If you set the Document Color Mode to CMYK, it leaves the CMYK values alone.
But as soon as you change the Color Mode, it automatically modifies the values. So if you were in RGB mode and you set some RGB values, it changes those RGB values when you switch to CMYK mode. And vice versa.
I had thought that the CMYK palette was a subset of the RGB palette. It would make sense to me if it did this when I switched from RGB to CMYK mode, but it doesn't make sense to me why it does this when I switch from CMYK to RGB mode.
The other thing I am confused about is the relationship of the values in the RGB boxes to the values in the CMYK boxes. I would have thought that the relationship between them would be static. Actually, it is not. When I am in CMYK mode and I enter a CMYK value of 90 16 0 0, the RGB values become 0 158 222. But when I switch over to RGB mode, the RGB values of 0 158 222 result in CMYK values of 75 23 0 0.
Very confusing.
Thanks in advance if you can explain this behavior!
Best Regards,
Z.

Color management.
Hi, I am struggling to understand why Illustrator is changing the values inside the RGB and CMYK boxes. I am also not sure of the exact relationship between these values. Essentially, it appears that if you set the Document Color Mode to RGB, it leaves the RGB values that you type in alone. If you set the Document Color Mode to CMYK, it leaves the CMYK values alone.
An Ai document can be either RGB or CMYK. The colors follow the document color mode and thus are converted immediately if they don't match.
But as soon as you change the Color Mode, it automatically modifies the values. So if you were in RGB mode and you set some RGB values, it changes those RGB values when you switch to CMYK mode. And vice versa.
Same reason.
I had thought that the CMYK palette was a subset of the RGB palette. It would make sense to me if it did this when I switched from RGB to CMYK mode, but it doesn't make sense to me why it does this when I switch from CMYK to RGB mode.
It's not. CMYK color spaces (there are more than just one) are normally smaller than RGB color spaces, but they aren't a "subset".
The other thing I am confused about is the relationship of the values in the RGB boxes to the values in the CMYK boxes. I would have thought that the relationship between them would be static. Actually, it is not. When I am in CMYK mode and I enter a CMYK value of 90 16 0 0, the RGB values become 0 158 222. But when I switch over to RGB mode, the RGB values of 0 158 222 result in CMYK values of 75 23 0 0.
When Illustrator converts the colors, it uses color management: the profiles you set up and the methods you set up. After converting it forgets the color that used to be. When converting "back", it uses color management again.
When you convert an very bright RGB color, it be out of the CMYK gamut. So it get's converted to the closest possbile CMYK color (which might still be far away from the original color. But it's not possible to convert it "back" to the bright one unless you just revert the conversion (by Cmd/Ctrl + Z).

Conversion rgb in cmyk

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