Digital File & RAW Formats Usage in UAV Aerial Photo Aquisition

Digital cameras are versatile devices, capable of recording images in many file formats. Common formats include JPG, BMP, TIFF, and many others, and their relative advantages and disadvantages are explained here.

What Is a File Format?

Simply put, a file format is just a particular way of encoding information for storage in a computer file. Computers are binary devices (operating with a number system of only 1’s and 0’s), so file formats can be thought of as a way to convert back and fourth between the original information and it’s binary representation. There are many different file formats, and some are more flexible than others. For example: the GIF file format can be used as a container for images or simple animations, while the JPG format can only store simple images.

Different file formats are identified by what’s called the file name extension. Adding a dot to the end of the file name and appending the abbreviation of the file format lets both people and programs know what the file format is. Changing the file extension doesn’t convert the file to another format though – it’s best thought of as a “note” or reminder of how to treat the file.

File formats are also identified by internal markers, usually strings of characters in the header of the file. Using different methods to identify the file format helps to ensure that it’s always handled correctly.

Why There are Different Image File Formats

When an image is downloaded from a camera, it’s encoded as different lighting and color levels for each pixel on the camera’s charge coupled device (CCD) sensor. All digital cameras have a CCD chip, which consists of an array of light sensitive pixels. Each pixel generates an electric current when a photon strikes it, known as the photoelectric effect. This current is read from each pixel and then recorded in memory as a series of light levels and colors. Obviously, a long list of numbers isn’t a human readable image. Most often, this RAW file format is immediately converted to one which is more easy to use, such as a JPG or TIFF. The image can then be read by a computer and printed or rendered on a screen.

There are different image file formats so, depending on your project, you need to compromise between image quality, file size, and many other parameters.

Comparing File Formats

With so many different file formats to choose from, it’s useful to understand what each is designed to do, so that you can use the right ones for your project. Here are some of the most common:

• JPG / JPEG – The name JPEG stands for Joint Photographic Experts Group. It’s a “lossy” file format designed to compress image data, reducing the size of the resulting file with a minimal loss of image quality. JPEG is a standard, ISO certified file format, and is commonly used to transmit images on the internet. Because of this, it’s one of the most commonly used formats on digital cameras. The small file size allows a large number of images to be stored on a single memory card, making it convenient to use.Whenever an image is stored in the JPEG file format, some information is lost. Because of this, JPEG is not suitable for usage where the exact replication of the original image data is required.
• BMP – The BMP, or bitmap format, is one of the most simple. It does not compress images, and stores image pixels with a color depth of 1, 4, 8, 16, 24, or 32 bits. For example: a 32×32 thumbnail image appears small when displayed on the screen. Enlarging the image will show each pixel as a large block, reducing the image quality. BMP is not a lossless format, and the large file sizes make it unsuitable for transmitting over the internet or storing on small memory cards.
• TIFF – TIFF stands for Tagged Image File Format. Designed to store images such as photographs and line art. The TIFF file format specification is currently owned by Adobe Systems. TIFF was designed to encode image data simply, in a single file, through the use of header tags defining the image size and other parameters. TIFF is a lossless format, meaning that no image information is lost when the file is compressed. This means that it can be edited and re saved without losing quality. TIFF is the preferred format for high color depth and high quality digital cameras. The files produced using the TIFF format are generally larger than equivalent JPEG files, but this is because of the lossless compression used by TIFF.
• GIF – The Graphics Interchange Format is a bitmapped file format, supporting 8 bits per pixel and a reference palette of 256 unique colors. The GIF file format can be used to create animations, and is sometimes used in websites. The GIF format is not used in digital photography, because of it’s quality limitations.
• PNG – The Portable Network Graphics format is similar to the GIF format, in that it uses lossless data compression, but PNG does not support animations, and it can use more than 256 colors.
• Raw – The raw file format is significantly different than those mentioned above. It’s relative advantages and disadvantages are discussed below.

The Raw File Format

A raw image file contains the minimally processed output from a digital camera’s image sensor. Raw images are not ready to be printed or edited with graphics softare – they must be “developed”, or turned into a different format first. Raw images are best thought of as film negatives- they aren’t directly usable as an image, but contain all the information necessary to create one.

So why would you use a raw image? It turns out that every JPEG or TIFF you download from a digital camera was a raw image at some point, the camera just converted it. High end cameras allow users to control how their images are “developed”, but the amount of control you have over the process is usually fairly limited. In this conversion process, some of the raw information about what the camera saw is always lost.

If you’re interested in seeing exactly what the camera saw, without losing any information during processing, then using the raw image format is the best option. Raw images give the photographer a great amount of flexibility, allowing you to precisely control the brightness, contrast, sharpness and other variables. Using raw image files can help you capture the detail that you wouldn’t otherwise get if using a processed image format.

Here are some of the benefits of raw image files:

• Higher Image Quality – All the processing takes place in one step, improving the final image quality.
• Better Intensity Information – Raw image files have 12 or 14 bits of brightness information, as opposed to the 8 bits a JPEG can provide.
• Finer Control – When you “develop” your raw image files, you have complete control over many of the variables, including brightness, contrast, and many others.
• Remove Unneeded Processing – Most digital cameras do additional processing on the images they take, including sharpening and noise reduction.
• Better Manipulation Possibilities – Transforming images in large ways, such as by increasing the exposure of an underexposed image can result in artifacts. Using raw images minimizes these, because the image has not already been pre processed.

Raw image files also have a number of disadvantages, the most notable being the large file size. Raw Images are typically 6 times larger than an equivalent JPEG, which reduces the number of pictures that can be stored on one memory card. It also takes more time to download a raw image from the chip and write it to a memory card, necessitating the use of more expensive camera equipment.

Unlike the other, processed formats mentioned here, there’s no one specification for a raw image. Camera manufacturers use different formats for their products, and the formats are often un-documented. There are several free projects under development that can read raw image files, most notably the GIMP (GNU Image Manipulation Program). Dcraw is also capable of reading and editing many raw file formats. Both these programs run on Microsoft Windows, and UNIX like operating systems including Mac OSX.

Aerial Photography Police Applications of The Raw File Format

For any police or law enforcement organization, collecting aerial pictures as evidence is best done in the raw format. When you are obtaining evidence, you don’t want to miss a single detail. The raw file format was designed to faithfully record everything that the camera sensor sees. With the raw file format, you are guaranteed that you don’t miss any detail in your pictures due to processing.

Because the white balance and other settings are not set when the camera takes the picture, they can be adjusted after the images are taken to ensure maximum image quality.

Our Draganflyer X6 UAV was designed to give users the maximum choice in camera equipment. Because of this, it can be equipped with the Panasonic LX3 digital camera, which supports output in the raw format.

At the time of writing, both Adobe Photoshop CS3 and Sikypix support the Panasonic LX3 raw image format.