Digital Images



.JPEG (Joint Photographic Experts Group) and JPEG 2000

JPEG (and JPEG 2000) is the ideal form for photographic images and when size is an issue. JPEG can reduce the file size by a factor 10 without visible quality loss. It achieves this by compressing color information more than information about detail and by compressing fine detail more than coarse detail, considering the sensitivities of our eyes. All digital cameras can shoot at least in JPEG. All scanners offer that too.


.GIF (Graphics Interchange Format)

GIF is ideal for web graphics (for example logos, straight lines) and offers the possibility of animation and transparency. GIF is not recommended for photographic images. The number of GIF images I get via e-mail is a clear signal there is confusion about the right image format. Saving a photograph as a GIF will reduce the quality significantly because GIF supports only 256 colors. Besides, the file size will generally be larger than a 16 million color JPEG. The only exception would be small image icons (for example 48 X 24 pixels) with only a few hundred colors and where you want to avoid JPEG compression artifacts as these become large in proportion to the image (the 48 x 24 pixel image would have only 18 8X8 JPEG squares for instance).


.TIFF (Tagged Image File Format)

TIFF is a universal format that is compatible with most image editing and viewing program comes in 8 bits and 16 bits a channel versions and in PC and Macintosh format. It can also be compressed in a lossless way, internally with LZW or Zip compression or externally with programs like WinZip. It also supports layers like the Photoshop .PSD format.

While JPEG only supports 8 bits/channel single layer RGB images, TIFF also supports 16 bits/channel multilayer CMYK images in PC and Macintosh format. TIFF is therefore widely used as the final format in the printing and publishing industry.

Many digital cameras offer TIFF as an uncompressed alternative to compressed JPEG because of space and processing constraints only the 8 bits/channel version is used in digital cameras. Higher end scanners offer a 16 bits/channel TIFF choice but the color bit depth of the scan may be lower. If available, RAW is a much better alternative for digital cameras than TIFF.


.BMP (Windows Bitmap)

A Windows format without compression that is used by Windows operating systems (for example for your Windows desktop wallpaper) and certain Windows programs. It also supports alpha channels. You will normally not need this format.


.PSD (Photoshop)

The native format of PhotoShop Elements (2,3) and PhotoShop (7, CS, & CS2). It is the ideal format for editing because you can store all your layers, including adjustment layers, etc. Given the widespread use of Photoshop, the format is recognized by most other image editing and viewing programs, but not all the file (for example layers) may be read properly. So it is recommended to us this format for your own master copy, not for sharing with others.


.PDF (Portable Document Format)

Most of you will be familiar with this popular format from Adobe which is used for electronic document distribution. Adobe's website could not have summarized it better: "Adobe PDF is a universal file format that preserves all the fonts, formatting, graphics, and color of any source document, regardless of the application and platform used to create it. Adobe PDF files are compact and can be shared, viewed, navigated, and printed exactly as intended by anyone with free Adobe Reader software. You can convert any document to Adobe PDF using Adobe Acrobat." Although PDF is used more for documents than for images. Image contact sheets created by ACDSee 8 can convert to PDF for Internet sharing and are smaller file size then the original .JPEG or .TIFF.


RAW

Some digital compact cameras and most digital single lens reflex cameras and scanners also offer RAW. RAW files offer amazing possibilities, but you need a RAW converter to open them. Because the format is less universal, "third-party" RAW converters may not always recognize all the settings the way "native" RAW converters do. Unlike JPEG and TIFF, RAW is not an abbreviation but literally means "raw" as in "unprocessed". A RAW file is like a "digital negative" because it contains the original image information as it came off the sensor before in-camera processing so you can do that processing afterwards on your computer with RAW conversion software. Many of the camera settings (e.g. white balance and sharpening) can be adjusted when using RAW converters. It's a bit like a raw steak from the grocery store which allows you more flexibility in cooking it the way you want it, rather than one which is already cooked in the restaurant. The added benefit is that, unlike the steak, you can reprocess the RAW data over and again until you are satisfied, without any quality loss.


SUMMARY

• GIF is ideal for web graphics and offers transparency and animation.

• JPEG is ideal for photographic images where size is an issue (e.g. in the camera, for e-mail, or on websites).

• RAW gives you the most flexibility. While smaller than TIFF, it can hold more data, but it is less universal, and requires post processing.

• TIFF is often used for sending master copies to a printer or publisher.

• PSD is the ideal format to store the edited master copy of your image.

• PDF is the ideal format to create and exchange images or contact sheets.

• Camera guidelines: it is recommended to shoot your images in JPEG at the highest quality. For very important images and scenes with a large dynamic range, shoot in RAW. If RAW is not available, shoot those images which you intend to enlarge beyond 8" x 10" in TIFF.

Share |