Disk Preparation Guidelines for: Graphics Files

The following sections describe disk preparation for bitmap and vector graphics. Please call TVP at (256)353-8991 If you require further Information on preparing your graphic files.

Bitmap Graphics

A bitmap graphic is defined by a horizontal and vertical grid of picture elements (pixels) known as a bitmap. This bitmap format is best suited to high resolution works such as photographs and fine detail line art drawings. Bitmap graphics are created by Adobe Photoshop, Corel PhotoPaint, Paintshop Pro and other "painting" programs. TVP accepts bitmap graphics saved in the Tagged Image File Format (.TIF) and in the Adobe Photoshop-specific Encapsulated PostScript format (.EPS). Bitmap graphics fall into three categories: black and white line art, grayscale halftone (black and white photography), color halftone (color photography).

Line Art - Must be at least 600 dpi (preferably 1200 dpi) at the finished size, black and white mode only. To preserve smooth lines and fine detail, black and white line art should be scanned at the highest resolution possible, up to the maximum resolution of the outputting imagesetter. For disk supplied line art scans, 300 pixels per inch (ppi) is a bare minimum with 600 ppi and above being preferable. Having found a balance between file size and quality, TVP scans line art at 1200 ppi for 2400 dots per inch imagesetter output.

Halftones - Must be 300 dpi at the finished size, CMYK or grayscale mode only. Color and grayscale halftone images should be scanned at approximately twice the lines per inch (lpi) screen of the outputting imagesetter. TVP outputs halftone images at 150 lpi. For your reference, TVP currently scans halftones at 300 dpi. at the finished size.

Image Resizing--These scan resolutions assume the image is being used at the size of the original artwork. Bitmap image resolution is inversely related to image size. A 4" X 4" 600 ppi line art scan reduced to 50% in a layout program will produce a 2" X 2" 1200 ppi image. Similarly, that same 4" X 4" scan increased to 200% in a layout program will produce a 8" X 8" 300 ppi image. There is no way to increase both image size and image resolution without rescanning; artificially increasing image resolution in a program like Adobe Photoshop will simply increase your file size but not your image quality. Given a final image resolution of 300 ppi, black and white line art that will be resized should be scanned at a resolution dictated by the following formula: (final image height / original image height) X 300. Given a final image resolution of 600 ppi, the formula becomes (final image height / original image height) X 600. As stated above, 300 ppi for black and white line art is the minimum with 600 ppi and higher producing much sharper results. Halftones that will be resized should be scanned at a ppi dictated by the following formula: (final image height / original image height) X lpi X 2.

Halftone Functions - When saving grayscale or color images, all halftone and screen transfer options should be turned off. Leaving these settings on interferes with the normal halftone screen functions of an imagesetter and can cause increased print times and produce lower quality output.

RGB to CMYK- Our printing presses use Cyan, Magenta, Yellow, and Black (CMYK) inks to reproduce color on the printed page, bitmap images must be converted from RGB to CMYK prior to printing. This conversion typically results in a color shift. Vibrant reds, greens and blues tend to show the most color shift in the conversion from RGB to CMYK. All color bitmap images should be supplied to TVP in the CMYK color model.

Vector Graphics

A vector graphic is defined by a series of mathematical objects and paths. The vector format is best suited to logos, illustrations and other geometric graphics. Vector graphics are created by Adobe Illustrator, Adobe (Macromedia or Aldus) Freehand, Corel Draw and other "illustration" programs. TVP accepts vector graphics saved in the .EPS format by the following programs: Adobe Illustrator 1.1 and above, Adobe (Macromedia or Aldus) Freehand 4.0 and above, Corel Draw 3.0 and above. While primarily vector-oriented, the above named illustration programs can incorporate bitmap information into their .EPS files; allowing you, for example, to place a color photograph into an Adobe Illustrator or Corel Draw layout. Unlike bitmap graphics, vector graphics can be resized without loss of quality. Be aware however that any bitmap information embedded in a vector-based file is still susceptible to image degradation if resized drastically. The major concern when constructing vector files is path complexity. Files containing excessive numbers of paths, objects, and gradient fills often will not print. Redundant paths and curve control points should be removed whenever possible to speed printing and prevent errors. Unless you are paying for a spot ink, all color fills, gradients, and strokes in a vector graphic should be in the CMYK color model. Blends and gradients between spot and process colors are not printable.