Information & Frequently Asked Questions
Digital Printing and Bitmap Images
Wide format digital ink jet printers, like desktop inkjet printers, create an image using tiny drops of ink, the only difference being the ink is usually solvent based, water proof and durable. The artwork created for these printers consists primarily of bitmap (otherwise known as raster ) images.
A bitmap is a matrix of pixels (picture elements) each pixel has a colour associated with it, how these colours are defined within the matrix creates the image. Imagine a chess board being the matrix and each square being a pixel. Each pixel can be only one colour but it can be from a colour range (palette) of thousands. Resolution, usually expressed as DPI (dots per inch), is a measure of how many pixels there are in a certain area and is a vital consideration when creating artwork for wide format printing.
The higher the resolution the more detailed an image and the larger size it can be printed without becoming pixilated. Unfortunately the file size also increases with resolution. Colour depth (how many colours each pixel can choose from) also affect file size. So for the best quality printed image high resolution and a high colour depth is needed. This can lead to very large file sizes, fortunately bitmap creation and editing software uses many different techniques to compress the files, leading to smaller file sizes and different file types.
Some common bitmap file types are as follows, eps (encapsulated post script) .bmp (bitmap) .tiff (tagged image file format) .jpg (joint photographic experts group) .pdf (portable document format). Some if these file types are compressed and others not. The most commonly used file formats for printing are pdf and jpg which are compressed formats. Commonly used bitmap editing software packages are Adobe Photoshop, Corel Paint Shop Pro, Corel Paint, or Serif Photoplus.
Another choice when creating bitmaps is colour rendering. For printing purposes there are two common types, CMYK (cyan, magenta, yellow, black) or RGB (red, green, blue). RGB is the way colour is displayed on monitors and TV’s whilst CMYK is primarily a system used for colour printing. For wide format colour printing CMYK artwork will produce the most accurate colours rendition. RGB can be converted to CMYK but the colours may not reproduce accurately. The above is a very brief description of bitmap colour format and file types. Many books have been written about the subject. If you would like further information Contact Us or check out http://www.printernational.org/
Below is a check list for creating artwork for large format printing.
Please submit artwork in one of the following formats.
PDF. At 100% scale if possible. If 50% or 25%, size and % need to be clearly specified in file name or with order). There are always ways to optimise a .pdf. Make sure that the image dpi is downsampled to 150-200dpi and all images inside the file are saved as a JPG.
EPS. With jpg visual enclosed
JPG. When creating the file please choose the highest quality setting.
Generally image resolution between 150-300dpi is adequate for most situations, for large images 150 to 200 dpi is adequate. For smaller images (One sq meter or less) 300 dpi if sufficient.
Saving as a .pdf or .eps with embedded fonts is not always good enough, even if it looks OK. To avoid typeface (font) issues please convert fonts to curves (outlines, paths).
All graphics including vector graphic and images need to be in CMYK colour mode. No RGB or spot colours (spot colours are specific named colours). If you need any more information regarding the above then please Contact Us.