CTO Tech Blog

I recently received some digital photos from a friend and noticed that the files were named differently from the ones from my own camera.  I was wondering why different camera manufacturers would use different file formats, so I did a little digging.

Camera manufacturers are always trying to get an edge by providing better features and image quality.  Much of the image quality is determined by the lenses, but once the picture is snapped, the image data needs to be stored.  I had a look at the specs on a high end camera, the Canon EOS 1DS Mark III digital SLR and they listed the image format as:

DCF 2.0 (Exif 2.21): JPEG, RAW and RAW+JPEG simultaneous recording possible. Multiple options for recording images on two memory cards, and onto compatible external USB hard drives (via optional Wireless File Transmitter WFT-E2A)

Since this is a high end camera, I thought that someone considering this purchase would be well up on the terminology and acronyms, so I looked at one of the consumer rated models instead.  The Canon PowerShot SX 120 IS Digital Camera had two separate specs for file format and compression:

Design rule for camera file system, DPOF (Version 1.1) compliant

Still Image: Exif 2.2 (JPEG)
Movie: AVI (Image data: Motion JPEG; Audio data: WAVE (Monaural))

Thinking that maybe it was just common for Canon to use these acronyms, I checked other manufacturers and was greeted with terms like CCD-RAW, TIFF, DPOF, and BMP.  There are some important things to look for in a digital camera, but choosing the right specs to compare may depend on your personal needs. First some basics about image files.  Image data can be stored in two very basic formats; raster and vector.  Vector graphics are more suited to line and shape drawings, including 3D images.  The basic premise of vector graphics is to define a starting point for a line, then a direction and distance.  The direction can be on two planes (2D) or three (3D).  Other parameters such as colour, fill, and weight are also defined.  Vector graphics are commonly used in computer aided design (CAD) drawings.  Raster graphics use a method similar to that of a television screen where the image starts forming by defining a single dot or pixel, then moving to the adjacent pixel and defining it.  This would continue across one dimension of the image, then move to the next line or row until the entire image is formed.  The definition would include colour and intensity for each dot.  As you can guess, vector graphics take relatively less space to store because they can define large areas with just a few parameter definitions.  Raster graphics by contrast, must define each pixel in the image.  To combat this space requirement, a number of different image formats and compression schemes have been developed.  The best quality images have no compression, but take the most room.  Because of the detail that can be stored is raster files they are used as the storage format for cameras.  Here are some descriptions that may help:

CCD - Charge Coupled Device.  This is the special device in digital cameras that convert light to electronic data.  They are an array of microscopic devices on one silicon chip and usually number in the millions.  The term megapixel refers to the number of pixels in a CCD.  More pixels allow the CCD to detect more detail in an image.

RAW - This is not an acronym.  Image data is taken directly from the CCD and stored on the storage media.  RAW images are created very quickly, but take a lot of space.  If space is not an issue, then this is the best format for a camera.

DCF - Design rule for Camera File system.  This is a standard adopted by a number of camera manufacturers to define a standard format for camera images file systems.  The standard includes folder structure and EXIF formatted files and has been adopted by most camera manufacturers.

EXIF - Exchangeable Image file Format.  EXIF adds structure and photographic information to existing image formats to standardize the file structure and help compatibility.  Information such as shutter speed, camera manufacturer and orientation are among the parameters defined.  Various versions of EXIF are in use by most camera manufacturers today.

JPEG - Joint Photographic Experts Group defined this standard for image compression.  There are a number of levels of compression available which decrease the storage footprint at the expense of image quality.  If you're looking for a camera that can store many pictures, then look for JPEG formats.  A low level of compression will retain most of the image quality with a good saving of storage space.

TIFF - Tagged Image Format was developed by Adobe Systems in an attempt to create a common image standard for scanners.  TIFF acts as a container which defined the geometry and other parameters of an image and may contain images in other formats such as JPEG.  TIFF formats with embedded JPEG give the same storage saving as JPEG, but don't add much additional value.

DPOF - Digital Print Order Format adds definitions for output to images.  These definitions may include number of copies, output image size, orientation, and title text.  This standard was developed by a consortium of camera manufacturers to simplify printing of digital images.  DPOF was not widely adopted and has become unneccessary for digital printing.

BMP - Bitmap images were developed by Microsoft as a high quality uncompressed image format.  The large size of BMP images makes them unsuitable for cameras or as images on web pages.

PNG - Portable Network Graphics files are based on the BMP with the addition of compression for use on the Internet.  The compression of PNG results in too much image quality loss for most camera use.

While there are many other formats defined and in use today, I hope this sheds some light on what to look for when choosing an image format or a camera that uses them.