Wednesday, August 01, 2007

Raw File Essentials?

Digital SLR camera has raw file capabilities why?
For those new in photography hope this will i think this is a little help.

Why use Raw?

Most of digital photographers come to regard the raw file as being the digital equivalent of a negative.

Most cameras operate in 12 bit mode on each sensor, producing a range of 4096 levels of either red, green or blue. If you choose jpeg output (or if your camera gives you no choice) then these values are used to calculate 8 bit per channel pixels, each with only 256 levels of each color. How that calculation is performed depends on the settings for contrast, white balance and other variables that you have made on the camera or the manufacturer has programmed into the firmware.
In general it gives good results, but is only one of an infinite number of ways of handling the image data. Shooting raw enables you to take your own decisions with the help of software for handling these images. The kind of corrections to be in the raw images for the test described above would not be possible with jpegs - you need to get it very nearly spot on camera for good results.
Even with 8 bit images, you can of course continue to process them in Photoshop or comparable software.
However, you are coming from a different starting point, and the result of altering contrast or other parameters will always be to cut down the number of possible levels in the file. If you make too great adjustments, this reduction may even become visible as distinct steps in tone where there should be smooth gradients.

Digital negatives

Most digital photographers come to regard the raw file as being the digital equivalent of a negative. You can alter the exposure - as when making a print - and also change the contrast, color balance and the shape of the tone response curve. Software such as [b}Bibble, Photoshop CS/CS2/CS3, Nikon Capture, Aperture and Nikon View gives you really powerful control over the appearance of your images.
This doesn't mean you can be slack about getting it right in camera, but it does widen the possibilities available to you. My choice of software was Nikon Capture, you can carry out a very considerable amount of alteration of contrast and curve shape solving almost all the problems of shadow and highlight separation and producing high quality output. Similar facilities are available in the other software. Should you need to do further manipulation in Photoshop CS/CS2/CS3, then you can output from these programs as 16 bit per channel (48 bit) TIFF files to avoid any quality loss.

Disadvantages of Raw

So exposures made on the DSLR have been in raw format. Raw files are larger than jpegs and so your CF card will fill up quicker. With a 1Gb CF card get between 103 and 107 raw files, but could store roughly three times as many fine quality full size jpegs. However the cost of CF cards is low enough for this seldom to be an important factor, and with a 40Mb 'image tank' to hand I'm unlikely ever to run out of storage space while shooting. For longer-term storage, large hard disks are now relatively cheap, and a DVD will hold well over 400 raw images.
Larger files do mean longer write times. For most purposes the burst of 4 frames to the buffer to be enough, although the wait of around ten seconds for the next frame after this can sometimes seem a very long time. In very fast-moving situations I change to jpeg - it only takes a second or so on the DSLR - select the quality setting on the dial then change quality using the wheel at the front right.
Unfortunately the compressed raw mode offered by Nikon is totally impracticable, putting the camera out of action for around 4-5 times as long. It's a problem they have not yet been able to address with a firmware update.

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