There are so many different filetypes out there, how do you know which type of file to use? Here is a list of common file types and their main usage with a brief summary at the end.

JPEG or JPG: JPEG is a file type standard created by the Joint Photographic Experts Group. The file type is a compressed format that supports 8 bits per color chanel for a 24 bit color total (bit depth of 8 bits means you have 256 levels for each color. 8 bits to represent red, 8 bits to represent blue and 8 bits to represent green. 256 levels of each of these three colors can then be combined to give a total of 16,777,216 mixed colors (256 × 256 × 256 ). The compression rate of the JPEG format is around 10:1. It is the most common file format for images photographed with digital cameras. JPEG is a “lossy” format which can create artifacts and degrade the file when it has been edited and saved multiple times. JPEG does not support transparancy in a file. If you are going to capture and print directly or with minimal alterations or have finished editing a file and want a smaller file size (such as for website use), JPEG is a good choice. If you are going to do some heavy editing, or multiple edits and saves, or if you want transparent sections in your file, or if you aren’t sure if your exposure settings are correct (for manual shooting) you might want to use a different format.

TIFF: Tagged Image File Format is a flexible format for handling images and data within a single file. Files saved in the TIFF format are lossless and can contain EXIF data in the same file. TIFF format is a good choice to use when a file might need to be edited multiple times or have some major retouching or editing needs or if you want to preserve transparancy or layers.

RAW: a RAW image contains minimally processed data from the camera’s sensor. This means that whatever data was recorded when the image was taken is saved without being processed. Every camera manufacturer has their own proprietary RAW format. When using proprietary software provided with the camera, RAW is a very functional format to use. RAW files sometimes have a “sidecar” file that is associated with them that contains standard metadata (aka EXIF data file).

DNG: Digital Negative format is Adobe’s response to demand for a unifying camera raw file format. Most cameras don’t capture in this format but there is a free converter available from Adobe (click here for more information) and it is supported by later versions of photoshop, lightroom, and aperture. DNG files also retain EXIF data within the same file, eliminating the need for a “sidecar” file. If you need a RAW format and are also concerned about future compatability and support this is a good format choice.

PSD: Photoshop Document format stores an image with support for most image options available in Photoshop. These options include layers with masks, color spaces, profiles, transparency, text, alpha channels and paths. This is in different from many other file formats that limit content to provide streamlined functionality. Photoshop’s popularity means that the .PSD format is widely used, and it is supported by many other software products.

BMP: Bitmat Format. The term bitmap comes from programming lingo, meaning just a map of bits. The term bitmap implies one bit per pixel. This is a very old format and usually is not a practical choice for photographers as large images require very large files (it produces TIFF sized files without any TIFF benefits.

GIF: Graphic Interchange Format is a bitmap format that is optimized for the internet. GIF supportstransparancy, animation and a 24 bit color depth but has a restriction of only 256 colors per frame. This restriction means that you can’t use this format for images with continuous tones (like photographs). This is a decent format when you want clipart or logos or simple animations and don’t need a wide variety of colors but I’d recomment PNG instead for these types of files.

PNG: Portable Network Graphics is a bitmap format that is also “lossless”. This file format was designed to replace the older GIF format. PNG supports animation, transparancy and a larger color range than GIF. PNG is better than GIF at almost every aspect from compression (smaller file size) to color range, transparancy types, and animations. The only drawback is that it has limited to no support in some older browsers. PNG provides sharper text in files than JPEG but when using the format for photographs, PNG files are 5 to 10 times larger than JPEG with minimal improvement to clarity. If you are storing clip art or logos use PNG. If you are working with photographs, pick a different format.

Lossy vs Lossless: Lossy methods in some cases can produce a much smaller compressed file than any known lossless method, while still meeting the requirements of the application. Lossy methods are intended for human interpretation where the mind can easily “fill in the blanks” or see past very minor errors or inconsistencies. The main problem with lossy methods is the formation of noise or artifacts in the file which compound over time (multiple edits and saves) to seriously degrade the file from its original condition. Simply opening a lossy format file is harmless. Degradation comes from compression involved in the saving process.

Summary:

JPEG – use for photos on the internet
TIFF – use for photos to be printed
RAW – use as original file capture and original unedited backup
DNG – use an unedited backup file for future compatability
PSD – only use if maximum photoshop compatability is a necessity
BMP – DON’T USE
GIF – don’t use unless PNG compatability is a concern
PNG – use for web graphics, clip art and logos. don’t use for photographs.

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