There are numerous file formats available and which one you are going to use depends largely on what you’re going to do with the file. So which file format should you choose?

Capturing image with a camera

Usually you can choose between the uncompressed (RAW, DNG, TIFF) and compressed file formats (JPEG). To understand more the difference between RAW and JPEG file format, read the article What is the difference between RAW and JPEG format?

RAW (unprocessed format) – This is the original unprocessed image that the camera captures with the sensor. Use this format if you are going to edit images afterwards and you want to set the specific image parameters manually (like white balance, contrast, sharpness, etc). Different manufacturers provide their own version of raw format (it is not standardized!): Nikon (.nef), Canon (.crw, cr2), Kodak (.kdc, .dcr), Minolta (.mrw), Pentax (.ptx, .pef), Sony (.arw, .srf), Panasonic (.raw), and so on (read below about .dng format). Note that some raw files are nothing more but tiff files and could also apply some camera processing to the image. I always shoot in this format.

DNG (digital negative format) – Created by Adobe in an attempt to standardise raw formats. Some newer cameras already have it as an option, so I highly recommend using it if available (instead of raw).

JPEG (Joint Photographic Experts Group; pronounced »jay peg«) – It is the most commenly used format when you are concerned about the use of space and you do not want to edit images afterwards. It is really a data-compression technique: the file size can be reduced to as little as 10% of the original. There are usually different quality levels available, depending on the amount of compression used (the quality of the image and its size change parallel): usually named High, Fine, Normal, Basic. If you choose to save the image directly in the jpeg format, the image is applied with not only compression, but also contrast, sharpness, white balance, saturation etc. (depending on the settings of the camera)! If your camera doesn’t have the option to shoot in raw (and if you don’t want to edit the images manually after shooting), I recommend you choose the tiff format or the best jpeg option your camera allows you.

TIFF (Tagged Image File Format) – It is a format that uses compression, but it doesn’t nacessarily loose information while compressing (like jpeg does): it has different compression levels, from lossless (it is compressed with no loss of data), to lossy. Just like with jpeg, camera applies some of the settings to the image prior to saving. In the last years it has been replaced with the raw format, which is smaller and retains more information.

If you do not want to bother with editing images afterwards and just want to shoot-show (either on the web, tv or print), ignore the raw files and just use best quality jpeg. It’s good enough.

Editing images

When editing images in programs such as Photoshop, it is always best to use the native file format. Avoid using any format that compresses images in any way (like jpeg) because every time you are going to save that file it is going to do another compression again and again, consequently ending up with much lower quality image (if you still prefer to use .jpeg, always make sure you are working on a copy of the original).

PSD (Photoshop document) – This is a native format of Adobe Photoshop program. It supports layers, colour management, 48-bit colour.. When editing image in Photoshop always save it in the .psd format so you can come back and change the edits you’ve made.

PSB (Photoshop Large Document Format) is used when saving documents larger than 300,000 x 300,000 pixels in Photoshop. It can only be opened by Photoshop CS or later.

DNG (digital negative) – I highly recommend converting any raw images into this format for archival and other purposes. Most companies that make digital cameras have their own raw format, so to be sure you will be able to open your images in few years time, it is best to use an open format, which dng is. You can convert the images inside programs (eg. Adobe Photoshop Lightroom) or with free Adobe DNG converter found on Adobe website (it is available for both Windows and Mac).

TIFF – If you don’t have any of those formats above available, use tiff. It can store levels and selections (alpha channels), supports different compressions.. The images can be stored as black&white, grayscale, in 24-bit, 48-bit, RGB, Lab, CMYK. It is supported by most applications.

To save an image in a different file format just open the image in an image-editing program and choose file/save as. Then in the save as dialog-box choose a different file format (usually in a drop-down menu).

Print

Depending where you want to print. Usually you can just use jpeg (best quality of course), for more advanced printing, I would recommend using PDF format.

PDF (portable document format) was developed by Adobe and is originally a native file format of Acrobat. It is based on PostScript. It has many advantages: embed fonts, accurately color-manged, supports 16-bits, preserves original layout, can be used on all platforms, is supported by many programs.. You can print documents in high resolution and at the same time have a small file size. Do not use this format for editing photos!

Emailing, publishing on the web, showing on the monitor

JPEG (Joint Photographic Experts Group) – It is the favourite format to use for the images on the web or for sending images via email. The quality loss is minimum (but still depends on the compression!!!). The file size is bigger the more contrasting the lines in the image are.

GIF (graphic interchange format) – Only use it (conditionally!!!) when transforming images into grayscale.

PDF (portable document format) – When you want to send PSD images to people who don’t have Adobe Photoshop installed on their computers. When you want to add security to a document. Do not use this format for editing photos!

Formats that you should NOT use for photography

GIF (graphic interchange format) – This is a format for graphics where you have large areas of even colour (WHILE images have smooth tone transitions!!!). It is mostly used on the Web because of some of its useful features: transparency, animation, progressive display when downloading. It can handle only 256 colours. Used mostly for animation, logos, charts, dialog boxes, line art..

JPEG 2000 – It has extensions like .jp2, .jpx, .jpc. Not all applications support it (Photoshop does) and is not supported with web browsers (so you cannot use it on the internet). It allows you to download the lower-resolution image first and let you decide whether you want to see the image in its original quality. It also allows you to choose parts of the image that are important to you, consequently using less compression on those parts.

PICT is a native format for Macintosh graphics. It supports both bitmap and vector graphics. It is being replaced by .pdf.

BMP (Windows Bitmap Format) – is a standard bitmap file format developed by Microsoft.

PNG (Portable Network Graphics) was designed to replace GIF.