Halftone screens and duotones

• Halftones are conversions of continuous tone art, such as photographs, to a form which can be represented
  with printer's inks, which are "flat"; and do not allow for shading.
         
• In line art, shading is accomplishing through use of small line "crosshatching" detail;
        
• Printer's ink is black; how do you get shading detail?

       Halftone process

•  Printer makes a halftone negative by placing a screen between art and film when making a printing plate.
         
• Screens have dots which, when ink is applied on the press, will reproduce as small, irregular dots which our
   eyes see as shading via a process called "visual fusion"

Types of screens

        Newspapers - 60-85 line screens;
        Magazines and catalogs - 130-150
        Laser 300 and above
       The finer the screen, the closer together the dots

Color separations

•    Color separations are actually halftones--each of the CMYK colors is represented as its own halftone,
     and then they are slightly  overlayed to produce the effects of color
• 
     
• The overlay process is called "color registration"; good reg can be seen close up in a magnifying glass or photo loupe as
     a "rosette pattern" of dots; bad reg is often the result of "moire patterns" which look like a visual mortise or
     shimmery pattern.
   

Color -- What separations consist of:

•  When white light is directed through a prism the result will be a rainbow effect depicting the visible
    Color Spectrum.
             
• Different wave lengths of light emerge from the prism at different angles
             
• In nature we often see this effect when light passing through water or ice particles produces a Rainbow.
             
• Primary or Additive colors-- Red Green and
  Blue light,  produces White, or in effect create the reverse of the prism spectrum.
   
•   Subtractive Color:
    Light reflecting off an object (even a photograph) gives us the sensation of color because from the
    white light, some colors have been absorbed by the objects surface and we can not see them
     (subtracted).
             
• To record and reproduce the object on multiple surfaces (i.e. pictures on paper), the
  reflected light has to be separated into Subtractive Color components that can then inturn be
   combined using pigments (cyan, magenta, yellow - black is added to this mix as a key color).
             
• The resulting images will also appear colored to our eyes for same
  reasons i.e. absorption / reflection.
   

Additive & Subtractive colors

                           RGB color is all around us in the form of light, and is referred to as the
                           Additive color system.
                           
                           On our projector in class, Red, Green and Blue filters are placed in front of high powered spot lights
                            and  the three lights directed to the same surface, which produces overlapping; a white
                            area would appear where ALL three lights overlap.

            Where each light overlaps another we would see Cyan, Magenta or Yellow - the Subtractive color
            system components.

            How Color gets printed:

•  We cannot print onto a surface with light. A printing press requires pigments, or inks.
  
• The Subtractive color system (ink) in an attempt to match all colors of nature.
   
•  However, not only are the CMY pigments incapable of matching all colors,
      their imperfections allow the reproduction of far less color than our RGB
        devices. This raises many problems for the graphic reproducer.
             
• Process inks have to be translucent yet retain the ability to achieve set
  standards of density.
  
• Where ALL three spots overlap we would hypothetically produce black but the inability of man to
   produce perfect pigments results in a muddy or dark brown.

           Because CMY cannot produce Black we must add a fourth pigment to assist many colours
            reproduced on a press and make the application of 100% of CMY appear black. This fourth colour is
            indeed Black - often referred to as the KEY colour, hence the CMYK printing process.

            CMY and K values can be 0% for none (white) to 100% for full colour (percentage halftone dot size).
 

            Colors can be described from/to anywhere in the world by using one of several color reference
            systems:

•    RGB i.e. 135,243,39 (values between 0 and 255).
    
• HSB i.e. 289,100,50 (values = degrees,%,%).
                  
• CMYK i.e. 35,70,95,8 (values between 0% and 100% halftone dot size).
   
   Proprietary color matching systems i.e. Pantone, are used by designers to get around fact that what you see is not
  what you get on an RGB monitor trying to reproduce CMYK color.

Pantone Matching System - PMS spot color vs process color

• Spot color is the color you see when you define colors in Pagemaker.  Represents premixed, flat inks. Pantone is a
  proprietary color matching system (looks like paint chips in a swatch book).
  
• You can use one, two or three spot colors in a piece w/o being full color--when you move to four colors and color photos, you
  are using full color, or process color and need to use CMYK colors.
   

  Bitmaps and channels

            Bit is the basic and minimum value used by or referenced in a computer at both the electronic and
            software level. (Notice your file size references that may be 104Kb (example) or 104 thousand Bytes
            where a Byte = 8 Bits). Therefore a Bitmap is a map or organised array of pixels of Bit based
            information.

                               • Black and White images have only one CHANNEL.

                               • Greyscale images also have only one CHANNEL.

                               • RGB images have three CHANNELS.
           
 

            CMYK
            CMYK Bitmapped images present quite a different story although you've probably already guessed
            that they have four CHANNELS, and are referred to as 32Bit Bitmaps - 8Bits (C) + 8Bits (M) + 8Bits
            (Y) + 8Bits (K) = 32 Bits.

            Ink and Paper affects the result

           CMY pigments are far from perfect.
            The different bases that they are transferred to also differ greatly (even white paper is not all the same and can
            produce varying results). The best CMY pigments that man can produce contain elements of the
            other two colours - they do not absorb/reflect light perfectly.

            Black doesn't exist

           We cannot separate black, it has to be constructed once the RGB to CMY results are established.

            There just aren't enough colors

            Finally consider that we can only reproduce 10 or 11 million colors with CMYK processes.
            A 32Bit CMYK 4 channel bitmapped image therefore only maps the restricted number of reproducible colors.

Color Theory exercise:

1. Find three colors that you like using Color SchemerColor Schemer and make a logo in PageMaker using your name.