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images55   , 26

from Perth Amboy


Photography - Understanding Digital Image Formats

Images produced by digital cameras now rival the grade of our finest photographic film stocks. However the nature of a digital image shares almost nothing in common with the analog image captured within a film emulsion.

An image captured in film can be an incredibly complex physical object that features a life of its own, and could be interpreted directly by inspection together with the human eye. A digital image, conversely, is an electronic representation of the scene - a sequence of numbers specifying red, green, and blue light intensities that needs some form of software to render it in a visual form that can be displayed on a suitable imaging device, being a photo-printer.

When an image is captured digitally, it's done with a mosaic of light-sensitive electronic pixels. These pixels have been independent square-shaped photodiodes which are arranged as a large tiled surface. Well, large in the point of view of a single pixel, since as we were to enlarge the pixel towards the size of a kitchen hardwood, then the area covered by the entire image sensor would be about the same as exactly what a football stadium.

A normal medium-resolution digital camera might have about 4000 electronic pixels arrayed along one fringe of its image sensor, contributing to 2500 along the other, creating around 10 million pixels overall. The look sensor in this case could be said to have a 10 megapixel resolution.

Now, when a picture is recorded electronically, what each pixel around the sensor measures is the amount of energy the sunlight imparts to it during the photographic exposure. Or even in simpler terms, the brightness in the light. This large variety of numbers is known as the RAW format with the image. It is, in essence, the digital equivalent of the show negative (or positive when it comes to slide film), since it carries ALL the information linked to the exposure.

As it happens, you can't simply interpret these RAW image records in a color-by-the-numbers type fashion. If you assign the color and brightness of each and every pixel to a corresponding printed pixel over a piece of photographic paper, or on the computer screen, you would not see a pleasing representation with the scene that was photographed.

The explanation for this is that the way our eyes answer color brightness differs from the way electronic pixels answer it. Our eyes are less understanding of large changes in brightness than are electronic pixels. The RAW numbers should be processed in a way that compensates with this difference.

What this means is that many number crunching needs to be performed to get the best result from our RAW image before it is printed in any form. This can be done inside the camera if you need to immediately see a preview in the result on your camera's Vast screen. Or it might be done using complex image processing software on your laptop, once you have downloaded the look. Until then, the RAW image needs to be stored for later use.

Unfortunately, inside the race to conquer digital photography landscape, photographic camera manufacturers adopted a first-to-build is first-to-dominate philosophy and created their particular proprietary versions of the RAW image format. A Canon RAW image, therefore, is formatted differently than a Nikon RAW image to the exact same image. Due to the proliferation of RAW formats, image processing software is now offering to cope with hundreds of competing RAW image formats. Used this is just not possible, which means that your imaging processing software (whether or not this comes from a vendor aside from your camera manufacturer) will probably support only the major RAW formats, such as Nikon's NEF format, Canon's CR2 format, and Fuji's RAF format.

It is likely to improve soon enough, however. Adobe has entered digital imaging fray by publishing a wide open standard for a RAW image format that it calls Digital Negative, or DNG. Slowly, camera manufacturers, like Hasselblad, Leica, Ricoh, and Samsung are building DNG support within their cameras, and with luck the larger players in the field will follow suit.

What this means, let's assume that a standard such as DNG is adopted, is the fact that when a photographer captures a picture, stores it in RAW format, after which forgets about it for A decade, they won't discover, once they get around to retrieving it again, that the image format continues to be obsoleted and there is no longer any software that can render the file right into a viewable and printable image. For big corporations with numerous archived images to preserve, this type of problem represents a logistic nightmare, in fact it is very costly to stay ahead it.

In the long run, a standardized RAW format will guarantee archival integrity of images, reduce headaches for unwary photographers all over the world, and save both of them time and money. DNG support is available in Adobe software packages for example Photoshop, and Photoshop Elements, and may likely migrate to 3rd party image software programs as the standard is embraced. Adobe also offers a free Digital Negative Converter looking at the site which allows forward-thinking photographers to change their existing RAW image format files into a DNG version as well.

As has been mentioned, software is required to convert a RAW format image into one that can be displayed and printed. This is analogous to the "development" process for negative film. The most typical image display format is JPEG (which represents Joint Photographic Experts Group). The JPEG format is a that can support a lot of compression, so that the final viewable image is substantially smaller in size (number of bytes) than the RAW image file. This implies it can be sent to others easily, via email for example. The JPEG format can be an industry standard image format, so the file can be opened and read by all commercial image processing software plus a large number of open source image software programs.

Another standard image format is TIFF. However, TIFF file sizes are generally much larger than those for your equivalent JPEG image, in order that they are used mostly by pros who need to produce large print reproductions with higher resolution. In fact, the DNG standard is founded on a version of TIFF.

Various image processing algorithms are used on RAW images to convert them into printable form. For example performing white balancing, the actual means by which an unwanted overall color cast is removed from the image. Every time a color cast is present, a photographed all-white object will render by having an off-white component that subtracts from image fidelity. The RAW image stored through your digital camera will likely have a very record of the white balancing correction used when the image was created, but you're free to adjust this when editing the style derived from the RAW format.

You will need to appreciate that when you are attempting to the create the best possible printable image, you have to start with the original RAW image file. When a printable version has been given, such as a JPEG version, the applied image processing algorithms have "tossed out" significant amounts of image information that was deemed unnecessary. These lossy operations are irreversible, and they also limit your remaining alternatives for tinkering with the image should you decide that the result is not quite what you are after. The perfect solution is is to return to the RAW format file and initiate over.

Because the differences in file sizes are very great, if you are not interested in collecting RAW image files and processing them for the perfect image later on, you should consider allowing your camera to create JPEG images since the default, and disregard the RAW format altogether. This may improve the responsiveness of one's camera, because you don't need to store the large RAW images to your memory card. If, for instance, you are photographing a sports event, your frame-rate when shooting within the continuous mode will likely be greatly improved. Also, you'll be able to record a greater number of images in your memory card before it fills up.

However, if you will be photographing something worth addressing, do consider the implications of not using the RAW format to record your images. You might regret it later.