Image File Formats  |  Image Color-Modes  |  Image Meanings

Image File Formats

PSD (Photoshop format) is the only format supporting all available image modes (Bitmap, Grayscale, Duotone, Indexed Color, RGB, CMYK, Lab, and Multichannel), guides, alpha channels, spot channels, and layers.

BMP is Windows image format. BMP format supports RGB, Indexed Color, Grayscale, and Bitmap color modes, but does not support alpha channels.When a BMP is imported, the entire file is embedded into the document.

DCS 2.0 (Desktop Color Separations) format, a version of the EPS format, lets you save color separations of CMYK images. This is nice for proofing designs with large hi-res files because the image includes a small 72dpi preview file which prints quickly. Select: Photoshop DCS 2.0: "Single File with Color Composite (72dpi)".

Another important reason to use DCS 2.0 is because it is the only format that can export images containing spot channels (like PMS colors) for CMYK process plus spot-color printing jobs (go to the 'channels' palette, from the pop-down arrow select 'New Spot Channel…', in that window click on 'color', for PMS colors click 'custom' and type in a PMS number, set 'solidity' close, save file as DCS 2.0 with 'single file-color composite'.

EPS / Photoshop: (Encapsulated PostScript)) language file format can contain both vector and bitmap graphics. EPS format supports CMYK, RGB, Indexed Color, Duotone, Grayscale, and Bitmap color modes, but does not support alpha channels. EPS supports clipping paths; when saving, set the "Device" to "3" for efficient output). EPS creates its own preview image which is included in the file. EPS saved with a Mac/JPEG preview has an accurate color preview (better than TIF, which relies on the application it is being imported into to create the color preview). Note: EPS files require Adobe Postscript® language printers to print properly (If the printer is not Postscript, it will print the preview file which will print ok only if the file size is reduced significantly).

EPS / Adobe Illustrator: this is an EPS vector graphic (with a bitmap preview). It is the preferred format for logos because it is size-independent, can print as spot colors or CMYK, can have a transparent background, can be used on vinyl cutting equipment, can be edited/manipulated easily, and has a small file size. (The small size is because the file is based on filling in areas of color defined mathematically as points connected by lines, not by colored pixels).

GIF (Graphics Interchange Format) is used to display indexed-color graphics in HTML documents over the Web. GIF is an LZW-compressed format designed to minimize file size and electronic transfer time. GIF format preserves transparency in indexed-color images; however, it does not support alpha channels.

JPG / JPEG (Joint Photographic Experts Group) format is used to display RGB photographs and continuous-tone images in HTML documents over the Web (CMYK-JPG images will produce an error in web browsers). JPEG format supports CMYK, RGB, and Grayscale color modes, but does not support alpha channels. Unlike GIF format, JPEG retains all color information in an RGB image but compresses file size by selectively discarding data.

PDF (Portable Document Format) is Adobe's flexible, cross-platform, cross-application file format. PDF files incorporate the document's fonts, and accurately displays layouts with both vector and bitmap graphics. In addition, PDF files can contain electronic document search and navigational link features. Adobe Illustrator can save, and open for editing, PDF files incorporating vector images and text!

PCT / PICT format is used in Mac OS graphics and page-layout applications as an intermediary file format for transferring images between applications. PICT supports RGB images with a single alpha channel, and indexedcolor, grayscale, and Bitmap-mode images without alpha channels. PICT is especially effective at compressing images with large areas of solid color. When a PICT is imported, the entire file is embedded into the document.

PNG (Portable Network Graphics) is an alternative to GIF. PNG format is used for lossless compression and for display of images on the Web. Unlike GIF, PNG supports 24-bit images and produces background transparency without jagged edges in grayscale and RGB (some Web browsers do not support PNG). PNG format supports RGB, indexed-color, grayscale, and Bitmap-mode images without alpha channels.

TIF / TIFF (Tagged-Image File Format) is used to exchange files between applications and computer platforms. TIFF format supports CMYK, RGB, indexed-color, and grayscale images with alpha channels and Bitmap-mode images with background transparency. (Photoshop can save layers in a TIFF file).

Image Color-Modes

Bitmap - black & white. (Colors can be applied easily, with transparent backgrounds, if saved as a TIF and imported into a layout application.)

CMYK (Cyan,Yellow, Magenta, Black) - process color separations for commercial and some desktop printing. Duotone (monotone, duotone, tritone, quadtone)- spot color (like PMS) only supported in EPS file format.

Grayscale - 256 shades of gray. (Colors can be applied easily if saved as a TIF and imported into a layout application.)

Indexed Color - colors specific to that document only. Used to minimize file size and electronic transfer times.

RGB (Red, Green, Blue) - used for monitor displays, projectors and most desktop and photographic color printers.

Spot Color - not a mode, but available in Duotone mode (saved in EPS file format) or CMYK mode with spot-color channels (only available when saved in Photoshop DCS file format)

Image Meanings

Hi-Res (High-Resolution) a large-sized and highly-detailed bitmap image for publishing and printing

Low-Res (Low-Resolution) a small-sized bitmap image used as a place holder for a hi-res, or for proofing, or for web and Powerpoint use.

DPI (Dots-per-inch) bitmap image measuring method (similar to PPI)

PPI (Pixels-per-inch) bitmap image measuring method (similar to DPI)

Pixel Depth - the amount of data used to relate the color information of each dot (pixel) on a computer screen. Monochrome is 1 bit deep. Greyscale=8. RGB=24. CMYK=32 bits deep.

PMS color (Pantone Matching System®) - color matching system for printing inks used on printing presses

Process color - the four-color printing process (Cyan, Yellow, Magenta and Black inks) used in commercial printing

Vector format - preferred format for logos because it is size-independent, can print as spot PMS colors or CMYK, can have a transparent background, can be used on vinyl cutting equipment, can be edited/manipulated easily, and has a small file size. (The small size is because the file is based on filling in areas of color defined mathematically as points connected by lines, not by colored pixels). Available in Adobe Illustrator, Macromedia Freehand, and Corel Draw applications.

Raster format - any image defined by colored pixels (commonly called Bitmap format)

Bitmap format - any image defined by colored pixels (or specifically a black & white pixel image)

Clipping Paths - Vector information in the 'Path' palette of a bitmap image used for selecting an area of the image and most importantly for saving the file so only the image within the clipping path will print when imported into a page-layout application, and the background can be set to transparent.