Digital File Formats – JPEG, TIFF, RAW, DNG

In many ways, digital photography is about options and selecting the proper file format for the type of photography that you will be doing. What some photographers forget is that selecting the proper file format when capturing the image is analogous to selecting the proper film in a 35mm cameras. It is analogous but not identical because film selection encompasses color temperature (i.e. white balance) and the color saturation which are not controlled by the file format.

The first thing to do is learn a little about the different file formats and their pros and cons, then see when to use each one.

JPEG – Joint Photographic Experts Group

Nearly every digital camera on the market has the capacity to save a JPEG file. This is a lossy file format which makes the file as small as possible by throwing out some image information. The information that is thrown out can not be recovered.

Pros:

File is small which means you can fit more images in a memory card.
Fast saves to memory cards, which means you can take more images per second.
Open standard format can be universally viewed by nearly any web browser, computer and image editing program.
If the image is properly lit and the exposure is properly set, the image quality is quite good for prints similar to slide film.
Option to set image quality to low, medium and high to control quality of image. High is the best image quality. (Some manufacturers use different names for the 3 quality settings.) (See Figure 2 and Figure 3 below).
Often you can set the image resolution which lets you save a smaller image that is easier to post to the web or send by e-mail without any post processing.
Prefect format if you are planning on doing some limited image editing on the computer.

Cons:

File is reduced to an 8 bit per channel image which can only represent 256 shades for each (red, green, blue) color.
Image is compressed by taking pixels of similar color and making them the same color.
Every time the image is saved more of the image data is lost. You will probably not notice any significant change in image quality until you have saved it 10 or more times for a 1 megabyte image file. More saves are required before significant image degradation can be noticed in larger images. (See Figure 1 below).
Wrong format for images that will be heavily manipulated in a photo editing program.
Camera processes the image when saving it to JPEG so some image information is lost which means that the photographer still need to make sure that they set the camera properly for white balance, color saturation etc.

When to use:

Snapshots of family and friends that will not be edited beyond simple cropping and red eye reduction (use the high image quality setting).
Images sent by e-mail (use medium or low image quality setting).
Documenting through images like your furniture in case your home is damaged or robbed (use high image quality setting).
If all the camera settings are on automatic, then chances are JPEG will be fine.

TIFF - Tagged Image File Format

This is another open standard file format that can be viewed in nearly any photo editing program. Its strength is also its weakness. The file, whether compressed or not, does not lose any image data. The flip side of this is that the file is much larger than a JPEG and even some RAW formats because all the image data is intact. This option is usually available instead of RAW.

Pros:

No image data is lost.
Better image quality than even the JPEG fine quality (See Figure 5 and Figure 6 below).
Good for images that will be heavily manipulated in a photo editing program.
More tolerant of poorly exposed images – similar to print film.
Saved at the camera’s max color bit depth, which is probably 12 bit (or higher) per channel image which can represent 4096 shades for each (red, green, blue) color. (This is only important if you are doing a lot of digital manipulation of the image – it will not add any visible quality to the image.)

Cons:

File size is very large, resulting in slow saving of image between shots.
Camera processes the image when saving it to TIFF, so the photographer still need to make sure that they set the camera properly for white balance, color saturation etc.
Still need to make sure that exposure, white balance and color saturation are properly set because fixing these in the photo editing program will degrade the image to a certain degree.
Overkill for typical snapshots or to send by e-mail.

When to use:

If you do not have RAW and are taking images that are important or will be heavily worked on in a photo editing program.
Weddings and other once in a life time images.
Fine art images.

RAW –Unprocessed camera image capturing data

This is the raw data that the camera gets from its image capturing chip and saves. It has not been manipulated in any way. It is extremely preparatory and can be different from camera to camera. It can be read directly by some high end image editing programs like Photoshop and Aperture. With this file format, you run the risk of not being able to read the file in 5 or 10 years because the files are not standardized. Any camera that saves RAW files will also come with software to convert the file to JPEG, TIFF and some other standard file formats.

Pros:

No loss of data between what the camera sees and what is in the file.
Exposure can be off by 3 stops or more and still be corrected in a photo editing program.
Camera settings like white balance, color saturation, etc. can be changed post exposure. Analogous to taking 3 slide film exposures at 1 stop over and under metered reading.
File size may be smaller than TIFF.
Saved at the camera’s max color bit depth which is probably 12 bit (or higher) per channel image which can represent 4096 shades for each (red, green, blue) color.
Option to save RAW and JPEG which is the best of both worlds. You get the photo quality of RAW as well as a JPEG to quickly see what the image is.

Cons:

Large file size means that it can take longer to save an image to the memory card, i.e. less images captured per second.
Difficult to work with images because they need to be converted to something else (like TIFF) before they can be easily shared and manipulated outside of high-end photo editing programs. You can work with the RAW file without conversion in the camera manufactures software and in some programs like Apples new Aperture.
There is the possibility that in a number of years the software used to view and convert RAW files will be so out of data that you will not be able to view the image with your new computer or software. This means you will need to save a copy of the image as TIFF or DGN to insure continued access to the image.

When to use:

Save as RAW + JPEG if the option is available on your camera. The JPEG image is just for you to quickly see what the image is before converting it or opening it. JPEG image quality, in this case, is not that important and low or medium quality should be more than adequate.
Weddings and other once in a life time images.
Fine art images.

DNG – Digital Negative

This is a format that was developed by Adobe (the makers of Photoshop) and is designed as an open standard “RAW” file format as opposed to the proprietary RAW formats that cameras generate. The idea is that if you save your image as DNG, it will be accessible by any program that can read those files long after the camera’s RAW file conversion program has become unsupported. Basically software developers would rather support one standard RAW file format called DNG rather than supporting a RAW format for each camera or manufacturer.

Pros:

Open standard that could (in the future) be incorporated within any photo editing program.
RAW file is part of the DNG file so the “original negative” is never lost.
Some camera makers like Hasselblad, Leica, Ricoh, and Samsung have started using DNG as their native RAW file format.
Developed by Adobe, a market leader in digital image editing software.

Cons:

Very large file because it also contains the original RAW file.
Not yet universally supported file format like JPEG and TIFF.

When to use:

I would not recommend using DNG yet if you have Canon or Nikon cameras because they will most likely have their RAW file formats supported for many years to come.
Use DNG as a backup to your RAW files and save them on separate CDs, DVDs or hard drives.

Examples