More about Offset Lithography

To continue with what I covered on Friday… leaving off with halftone and separation screens… rows and rows of tiny dots to allow a press to print an image. The key thing to remember when correctly sizing¬† the resolution of digital images comprised of pixels (little dinky squares) is you have to know the resolution of the halftone screen. Newspapers typically print screen resolutions of 85 lines per inch to 100 lines per inch (relatively coarse dot screen). Magazines typically print in 133 to 150 lines per inch (a finer screen) and commercial custom printing ranges from 150 up to 400 lines per inch (fine screens for ultra-high image quality). Take whatever the halftone/separation line per inch resolution is and multiply that by 2 to get the pixel resolution of the raster/Photoshop image. Digital images for newspapers should be at 170 pixels per inch. Anything for magazines or most commercial printers, the digital resolution should be 300 pixels per inch.

File formats from Illustrator and Photoshop.

Print design: high resolution (300 ppi)

  • .eps (encapsulated postscript) – best for vector graphics from Illustrator.
  • .tif (tagged image file format) – best for raster images from Photoshop.

Web design: low resolution (72 ppi)

  • .jpg¬† (Joint Photographic Experts Group format) – lossy image compression file format for images and graphics with a full-range of color and value. The higher the compression in a jpg image, the more the image is “damaged. jpgs are a raster/pixel-based image format. Illustrator, although vector based, can save/export raster images.
  • .gif (graphic interchange format) – image format can support 256 (8 bit color) colors. Also useful in that gif can strip out unused colors to make a smaller image file. Good for flat color, limited color graphics.
  • .png (portable network graphic) – Lossless image compression technology. Images can be compressed to make smaller file sizes without image quality loss.

Other than my drawing of 6 color off-set lithography printing press, I think these two posts cover that really long lecture I gave on Friday. Sorry, but it was necessary so as to know why you do different things in InDesign, Illustator and Photoshop.


Stuff to make your eyes glaze over.

Yes, I threw a lot of information at you today. But it isn’t that hard to remember. I’m going to do several/multiple posts to cover what I talked about.

Software: What we are starting with.

  • InDesign: Asset Management software – where the designs and assets from Photoshop and Illustrator are assembled. Essentially the digital drafting table where production art is assembled.
  • Photoshop: Image Editor – photography processing, illustration and graphics creation – Raster-based (Pixels).
  • Illustrator: Graphics Creation – logos, illustrations and graphics – Vector based (math-based).

Print-based information

Offset Lithography – big commercial printing companies. Big offset lithography presses can either print ink or not print ink. They do not print tonal ranges of the ink. 100% ink or 0% ink on paper. Two types of ink used in Offset Lithography – Process Inks = Cyan, Magenta, Yellow and Black (CMYK) and Spot Color Inks (Pantone Matching System – PMS) Spot color inks are physically mixed inks while Process (CMYK) inks are a visually mixed illusion of different colors and tonal ranges. Process inks are transparent and Spot color inks are typically opaque. Both process inks and spot color inks are subtractive color modes. Subtract from 100% to 0% of the four colors to get to white. To create the illusion of tonal range and full-color a mechanical conversion must take place in continuous-tone images (Photography and artwork). The images are converted into tiny little dots – a series of dots. These little dots are called Benday dots which allows for presses to reproduce images. When a black and white photograph is converted to a series of little dots it is called a Halftone. When a color image is converted and separated into four sets of colors (CMYK) of little dots they are called Separations. Still with me? I am trying to keep this a simple as possible. Don’t let eyes glaze. Pay attention here.

Web-based publishing  – Color modes used on the web are RGB (Red, Green Blue) and is an additive color process – Add from 0 to 255 (all three colors) to get to white.

…more to come. Stay tuned.