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June 30 2015

Photography - Understanding Digital Image Formats

Images manufactured by digital cameras now rival the quality of our finest photographic film stocks. But the nature of a digital image shares very little in common with the analog image captured within a film emulsion.

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

When an image is captured digitally, to control your emotions with a mosaic of light-sensitive electronic pixels. These pixels have been independent square-shaped photodiodes which are arranged by means of a large tiled surface. Well, large from the point of view of a single pixel, since as we were to enlarge the pixel towards the size of a kitchen porcelain tile, then the area covered by the entire image sensor would be about the same as that of a football stadium.

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

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

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

The reason behind this is that the way our eyes respond to color brightness is different than the way electronic pixels react to it. Our eyes are less responsive to large changes in brightness than are electronic pixels. The RAW numbers should be processed in a way that compensates just for this difference.

What this means is that many number crunching must be performed to get the best result from our RAW image prior to it being printed in any form. This could 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 computer, once you have downloaded the style. Until then, the RAW image should be stored for later use.

Unfortunately, from the race to conquer digital photography landscape, digicam manufacturers adopted a first-to-build is first-to-dominate philosophy and created their very own proprietary versions of the RAW image format. A Canon RAW image, therefore, is formatted differently compared to 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. In reality this is just not possible, which means your imaging processing software (when it comes from a vendor other than your camera manufacturer) may well support only the major RAW formats, for instance Nikon's NEF format, Canon's CR2 format, and Fuji's RAF format.

This situation is likely to improve in time, however. Adobe has entered the digital imaging fray by publishing a wide open standard for a RAW image format who's 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 more expensive players in the field will observe suit.

What this means, if a standard such as DNG is adopted, is the fact that when a photographer captures a picture, stores it in RAW format, and then forgets about it for 10 years, they won't discover, when they get around to retrieving it again, that the image format continues to be obsoleted and there is no longer any software that will render the file in to a viewable and printable image. For big corporations with millions of archived images to preserve, this kind 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 ensure archival integrity of images, reduce headaches for unwary photographers around the world, and save both of them time and money. DNG support is available in Adobe software packages such as Photoshop, and Photoshop Elements, and can likely migrate to third party image software applications as the standard is embraced. Adobe also offers a free Digital Negative Converter looking at the site which allows forward-thinking photographers to convert their existing RAW image format files in a DNG version as well.

As may be mentioned, software is had to convert a RAW format image into one that will be displayed and printed. This is analogous to the "development" process for negative film. The most common image display format is JPEG (which is short for Joint Photographic Experts Group). The JPEG format is certainly one that can support quite 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 on others easily, via email as an example. The JPEG format is additionally an industry standard image format, so the file can be opened and read by all commercial image processing software along with a large number of open source image software packages.

Another standard image format is TIFF. However, TIFF file sizes are often much larger than those for your equivalent JPEG image, so that they are used mostly by professionals who need to produce large print reproductions rich in resolution. In fact, the DNG standard will depend on a version of TIFF.

Various image processing algorithms are applied to RAW images to convert them into printable form. For example performing white balancing, which is means by which an unwanted overall color cast is taken away from the image. Whenever a color cast occurs, a photographed all-white object will render by having an off-white component that subtracts from image fidelity. The RAW image stored from your digital camera will likely have a record of the white balancing correction used when the image was created, however are free to adjust this when editing the picture derived from the RAW format.

You will need to appreciate that when you are attempting to the create the most effective printable image, you need to start with the original RAW image file. When a printable version has been made, such as a JPEG version, the applied image processing algorithms have "tossed out" quite a lot of image information which was deemed unnecessary. These lossy operations are irreversible, plus they limit your remaining options for tinkering with the image when you decide that the result is nearly what you are after. The solution is to return to the RAW format file and initiate over.

Because the variations in file sizes are extremely great, if you are not concerned with collecting RAW image files and processing them for your perfect image afterwards, you should consider allowing the digital camera to create JPEG images because default, and neglect the RAW format altogether. This will likely improve the responsiveness of the camera, because you don't have to store the large RAW images in your memory card. If, as an example, you are photographing a sports event, your frame-rate when shooting within the continuous mode will probably be greatly improved. Also, you'll be able to record a greater number of images for your memory card before it fills up.

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

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