USEFULL INFORMATION

WHAT IS ?

CMYK

Description : Stands for the colors Cyan-Magenta-Yellow-Black. In print design, colors are defined as a percentage of each of these 4 colors. For example, the CMYK abbreviation for the color black would be 0-0-0-100. In contrast, display devices (i.e. computer monitors) typically define colors using RGB.

RGB

Description : Stands for the colors Red-Green-Blue. In web design and design for computer monitors, colors are defined in terms of a combination of these three colors. For example, the RGB abbreviation for the color blue shown below is 0-0-255. In contrast, print designers typically define colors using CMYK.

DPI

Description : Stands for dots per inch. DPI specifies the resolution of an output device, such as a printer or printing press machine. Print resolution usually runs from 300-1200 dots per inch on a Laser Printer. (For information on input device measurements see ppi.)

PPI

Description : Stands for pixels per inch. PPI specifies the resolution of an input device, such as a scanner, digital camera, or monitor. Web page resolution ranges from 72-96 pixels per inch. (For information on output device measurements see dpi.)

FTP

Description : Stands for File Transfer Protocol. FTP allows you to copy or send files (HTML-documents, graphic images, spreadsheets) from one computer to another via the Internet.

HTML

Description : Abbreviation for Hypertext Markup Language; a cross-platform text-formatting system for creating web pages, including copy, images, sounds, frames, animation and more.

PDF

Description : Stands for Portable Document Format. Created by Adobe Systems in its software program Adobe Acrobat as a universal browser. Files can be downloaded via the web and viewed page by page, provided the user is computer has installed the necessary plug-in which can be downloaded from Adobe’s own web site.

File Formats Glossary

Vector File Formats

The most used vector graphics formats are:

AI - Adobe Illustrator graphics, CDR - CorelDraw vector graphics, SVG - Scalable vector graphics, WMF - Windows Metafile format, DRW - Vector drawing file, DWG - AutoCAD Drawing Database File

Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon(s), which are all based on mathematical equations, to represent images in computer graphics. A typical vector graphics file is your logo, broken down into a series of geometric shapes, consisting of outlines that are curved and joined at X Y coordinates or points. These coordinates and shape outlines are stored as mathematical equations (.EPS, .AI, .CDR formats) creating small and portable file sizes that are infinitely editable.Vector graphics usually are easily modified within the creating application and generally are not affected detrimentally by scaling (enlarging or reducing their size) compared to raster or bitmap image file types where image scaling reduces picture quality. Because vector elements are mathematically-defined, scaling simply requires modification of their mathematical locations.

The EPS file format

Description : Encapsulated PostScript (EPS) is a standard file format for importing and exporting PostScript files. It is usually a single page PostScript program that describes an illustration or entire page. The purpose of an EPS file is to be included in other pages. Sometimes EPS files are called EPSF files. EPSF simply stands for Encapsulated PostScript Format. An EPS file can contain any combination of text, graphics and images. Since it is actually a PostScript file, it is the most versatile file format that is available. To avoid the need for a PostScript interpreter, EPS-files usually contain a small preview image that is used to visualize its content.

EPS files can be generated by all drawing applications as well as most layout applications. Image manipulation programs like Adobe PhotoShop can also save bitmap images as EPS-files. Some printer drivers are also capable of generating EPS-files as well as PostScript files.

Raster File Formats

Description : In computer graphics, a raster graphics image or bitmap is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium. Raster images are stored in image files with varying formats.

EPS files can be generated by all drawing applications as well as most layout applications. Image manipulation programs like Adobe PhotoShop can also save bitmap images as EPS-files. Some printer drivers are also capable of generating EPS-files as well as PostScript files.

TIFF file format

Tagged Image File Format (abbreviated TIFF) is a file format for storing images, including photographs and line art the TIFF format is widely supported by image-manipulation applications, by publishing and page layout applications, by scanning, faxing, word processing, optical character recognition and other applications. TIFF is the format of choice for archiving important images. TIFF is THE leading commercial and professional image standard. TIFF is the most universal and most widely supported format across all platforms, Mac, Windows, Unix. Data up to 48 bits is supported. TIFF supports most color spaces, RGB, CMYK, YCbCr, etc.

BMP file format

Description : BMP is a standard file format for computers running the Windows operating system. The format was developed by Microsoft for storing bitmap files in a device-independent bitmap (DIB) format that will allow Windows to display the bitmap on any type of display device. The term “device independent” means that the bitmap specifies pixel color in a form independent of the method used by a display to represent color. The default filename extension of a Windows DIB file is .BMP.

Use in a prepress environment

Everything that can be done with BMP, can also be done with TIFF files (or EPS). Because TIFF is an established and more versatile file format for prepress applications, it is better to avoid BMP-files for prepress production. BMP is also limited to RGB-images only while CMYK data are prefered in prepress.

JPEG File Format

Description : JPEG stands for Joint Photographic Experts Group, which is a standardization committee. It also stands for the compression algorithm that was invented by this committee. To complicate things a bit more, JPEG compressed images are often stored in a file format called JFIF (JPEG File Interchange Format), which a lot of people also refer to as JPEG!

JPEG is a commonly used method of lossy compression for photographic images. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality. JPEG compression is used in a number of image file formats. JPEG/Exif is the most common image format used by digital cameras and other photographic image capture devices; along with JPEG/JFIF, it is the most common format for storing and transmitting photographic images on the World Wide Web. These format variations are often not distinguished, and are simply called JPEG.

JPEG supports RGB and CMYK color spaces.

GIF File Format

Description : GIF is a file format that should not really be used for prepress, it is far more suited for web design or to exchange images through e-mail or newsgroups. GIF is the abbreviation of Graphics Interchange Format. It was originally developed by CompuServe (an on-line service that was pretty successful in the early nineties). The format includes some key features which makes it a unique and valuable format for the internet. These features include file compression, transparency, interlacing and storage of multiple images within a single file which allows for a primitive form of animation. GIF image color palette is limited. A GIF image can contain 2, 4, 8, 16, 32, 64, 128 or 256 colors which are stored in a color palette or color table within the image file. Each color in the GIF color table is described in RGB values, with each value having a range of 0 to 255. CMYK colors are not possible in GIF. Although the GIF format has access to over 16.8 million colours, only a maximum of 256 colours can be referenced within a single GIF image. While this limited palette keeps down file size and is perfectly acceptable for on-screen viewing, it leads to posterized images when they are printed. Most preflighting tools like PitStop can generate a warning when they encounter images with a fixed colour palette. Although GIF does not require a specific resolution, most GIF images have a resolution between 72 and 90 dpi, ideal for on-screen viewing but insufficient for prepress use.

Resolution

Description : Resolution is the term used to describe the number of dots, or pixels, used to display an image. Higher resolutions mean that more pixels are used to create the image, resulting in a crisper, cleaner image. The display, or resolution on a monitor, is composed of thousands of pixels or dots. This display is indicated by a number combination, such as 800 x 600. This indicates that there are 800 dots horizontally across the monitor, by 600 lines of dots vertically, equaling 480,000 dots that make up the image you see on the screen.

In the context of editing photos, resolution is a measurement of the output quality of an image. The most common units to measure resolution include: PPI (pixels per inch), DPI (dots per inch), LPI (lines per inch), and SPI (samples per inch). For our purposes, we will focus on DPI and PPI because that is what you will be dealing with most often when printing photographs. MP (Megapixels) simply means "one million pixels" and is used when describing digital camera capability.

PPI or "pixels per inch" is the term you will see most often when selecting a resolution for your images in photo editing software. Pixel is an abbreviation for "picture element." Millions of pixels make up the image of paper and text that you are viewing on your screen right now.

So how do you best choose a pixel resolution for your photos?

First, you need to consider where you will use your pictures (in print or online) and how large they will appear. For best results, a good number to remember when printing an image is 300 pixels/inch at actual size. In other words, when you resize an image with photo editing software, set the dimensions of the image to the print size first (e.g. 5 x7) and then set the resolution to 300 pixels/inch. The lower the pixels per inch, the blurrier the image will appear on paper. Depending on your printer, you could get acceptable results from 200-300 pixels/inch. In contrast, an image from the Internet is typically only 72 ppi. When you try to enlarge a picture with such a low resolution further, you are asking the software application to make up for pixels that don't exist; the image will get blurrier. So, what pixel size do you need for great printing results with the least strain on your computer memory resources? Below is a quick reference chart.

- 5 MP = 2592 x 1944 pixels, High Quality: 10 x 13 inches, Acceptable Quality: 13 x 19 inches

- 4 MP = 2272 x 1704 pixels, High Quality: 9 x 12 inches, Acceptable Quality: 12 x 16 inches

- 3 MP = 2048 x 1536 pixels, High Quality: 8 x 10 inches, Acceptable Quality: 10 x 13 inches

- 2 MP = 1600 x 1200 pixels, High Quality: 4 x 6 inches, 5 x 7 inches, Acceptable Quality: 8 x 10 inches

Less than 2 MP

Only suitable for on-screen viewing or wallet-size prints.

As you can see, 2 MP is typically sufficient for printing great quality 5 x 7 photos. You may want to save your photos with a higher MP if you want to be able to crop sections out of a photo and still have quality composition.

IMAGE RESOLUTION FOR PRINTING

Optimal resolution for magazine-quality printing is 300ppi !

If you want to make a good 8x10 print under the above standards, it will be best to have a 300ppi image with a size of 2400 by 3000 (8x300 by 10x300), a 7.2Mpixel scan. Consider one thing when selecting resolution- you can always scale down your resolution but you cannot increase the resolution of an image. So, in this case, bigger is better if you can accommodate the extra file sizes on your computer and printer.

DPI specifically refers to how many dots of ink will print per inch. The higher the number, the sharper the image will be. Most ink jet printers today are capable of printing 1200 to 4800dpi, this means great results for images with 200-300 ppi.

Online or Screen considerations

The magic number for screen formats—TV, computer monitor, PDA or cell phone—is 72 ppi. The size in pixels (not in inches) determines how big on the screen you want your image to appear. If your monitor is set to 1024 x 768, then an image at that size set to 72 ppi will fill the screen. Since image size (dimensions) determines file size (the number of bytes, k) you shouldn't make the image any larger than necessary for sharing photos through email or online.