confused on CMYK and RGB

Discussion in 'Digital Darkroom' started by glenn_carroll, Feb 2, 2012.

  1. So I know about the different color space for different purposes (for the most part). sRGB = internet purpose. ProPhoto RGB = high quality prints. This is mainly because of the different in size of color gamut. What I don't understand is 2 things.
    1) What makes ProPhoto RGB so good if printers cannot output the colors anyway because it is so big. I mean, most places I go to like Bayphoto and Nations Photolab ask for adobe 1998 AND jpeg rather than TIFF. So if I want to make a great print (we're talking museum quality)...where do I go online?
    2) I'm thinking of making some posters with images from illustrator. Vista print asks specifically for the file to be done in CMYK because thats how the printers work with the image. OR they said send it in the natural illustrator.ai file type. after reading this thread (below)and some comments by Andrew Rodney (the apparent kind in this stuff), it seems like the people at vistaprint dont know what they're talking about. Andrew said all printers expect RGB colorspaces, so you need to give it to them. THEN they convert to CMYK
    http://www.photo.net/digital-darkroom-forum/00YjZ4?start=0
    so if some of these people are right, and CMYK is garbage to work in, why is it even available to work in? why would adobe products allow us to work in garbage colorspaces?
     
  2. Cyan/Magenta/Yellow/Black (CMYK) and Red/Green/Blue (RGB) are complimentary ways to describe the color space.
    They're not related to gamut.
    Red, Green, and Blue are the colors that the human eye sees, and are the only colors that matter for human vision.
    CMY(K) is used in the printing industry, and in color photography, because you can create the original
    appearance when you overlay filters of different characteristics.
    An example:
    Cyan = green plus blue
    Magenta = red plus blue
    Yellow = red plus green
    If you put a yellow filter on top of a magenta filter and look at a white light through the pair,
    you will see red, because that one color is passed by both filters.
    The same thing works with printing inks.
    Each color of ink (Cyan, Magenta, and Yellow) is a filter, and each passes two of the primary colors.
    When combined in varying proportions, CMY inks can reproduce any color in the visible spectrum
    ... except black. That's where the K (black) comes in.
    Using the complimentary ink colors (CMY) you cannot produce a clean black, so black ink is
    added to the printing mix for proper reproduction.
    - Leigh
     
  3. CMYK is a colour separation used when you print with Cyan, Yellow, Magenta and Black inks with printing presses. This is a subtractive colour model.
    See http://en.wikipedia.org/wiki/CMYK_color_model
    Cross posted with Leigh
     
  4. sRGB = internet purpose. ProPhoto RGB = high quality prints
    not really. sRGB is good for everything, even museum quality print. I develop my image in Lightroom using Pro Photo 16bit, but when i export them in Photoshop for final editing they are in sRGB. IF you have a high end inkjet printer like a epson 4880 for example, you can send it a Pro Photo image, and you will get some extra saturation on some color, but no lab as today take that, and i dont see the use at that stage.
    Photolab ask for adobe 1998 AND jpeg rather than TIFF
    and this is perfect. Even the Adobe 98 im surprise because most lab dont support it.. you get darker and less saturated print with nost of them. Safe bet is to do a sRGB JPEG quality 12. JPEG quality 10-12 is the exact same visual quality than a TIF..
    all printers expect RGB colorspaces... they convert to CMYK ...
    correct. Do all your stuff in Illustrator then save as or export as JPEG sRGB (witch is pretty close to a CMYK color space)
    CMYK is garbage to work in, why is it even available to work in?
    Because some people, mostly graphic designer need that to place in there layout, they dont want to do anything to the file and they want no responsability if thing go bad.. so they ask CMYK to the photographer, ven if they dont no much about this color space. Magazine need CMYK, lets give them CMYK.. but its a wrong thing to do as CMYK need specific specs to correctly work. Of course, you can just use the SWOP Coated v2 and live happy most of the time as the printer will convert your wrong profile to is good one in is server.. but why make 2 bad conversion? so by giving them a sRGB file, the file is still device independant so it can be use anywhere.
     
  5. digitaldog

    digitaldog Andrew Rodney

    Andrew said all printers expect RGB colorspaces, so you need to give it to them. THEN they convert to CMYK​
    Not quite. All Quickdraw and GDI printer drivers expect RGB data. They will then use their black box processes to create CMYK (or in the case of a modern ink jet, perhaps CcMmYKK, or add Orange and Green to the process). The point is, all printers end up using a subtractive process. Emissive output devices (your display) output RGB. There are tons of printers that will only accept CMYK data initially (you canโ€™t send RGB to an Indigo direct to digital press as an example). The front end RIP can accept RGB data. It will convert the RGB to CMYK. Much like an Epson or Cannon will convert RGB to CMYK or as many colorants it uses to print. Many RIPs will gladly accept output ready CMYK data. It all depends on the shop.
    As for color spaces (specifically RGB spaces like sRGB, ProPhoto), you might want to start here:
    http://www.adobe.com/digitalimag/pdfs/phscs2ip_colspace.pdf
     

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