Shooting in JPEG
When you shoot in JPEG the camera’s internal software (often called “firmware” since it’s part of the hardware inside your camera) will take the information off the sensor and quickly process it before saving it. Some color is lost as is some of the resolution (and on some cameras there is slightly more noise in a JPEG than its Raw version).
The major actor in this case is the Discrete Cosine Transforamtion (or DCT) which divides the image into blocks (usually 8×8 pixels) and determines what can be “safely” thrown away because it is less perceivable (the higher the compression ration/lower quality JPEG, the more is thrown away during this step). And when the image is put back together a row of 24 pixels that had 24 different tones might now only have 4 or 5. That information is forever lost without the raw data from the sensor recorded in a Raw file.
The quality of a JPEG taken with a DSLR will still be far better than the same shot taken with a top-of-the-line point-n-shoot camera that is as old as your DSLR. If your camera can burst (shoot continuously for a few seconds) you’ll actually be able to shoot more shots using JPEG than Raw because the slowest part of the whole process is actually saving the file to your memory card – so the larger Raws take longer to save.
Shooting in Raw
If you do shoot in Raw, your computer rather than the camera will process the data and generate an image file form it. Guess which has more processing power: your digital camera or your computer? Shooting in Raw will give you much more control over how your image looks and even be able to correct several sins you may have committed when you took the photograph, such as the exposure.
To take advantage of this you will certainly need to use some software on your computer to process the files and produce JPEGs (or TIFFs). I have found the Camera Raw that comes with Adobe Photoshop CS2 to be very good at processing Raw files (even batch processing them), though everybody has their favorite (RawShooter has a lot of fans). When you load a Raw file using Adobe Photoshop CS2 the Camera Raw dialog will automatically pop up. Most of the time the automatic settings are fairly decent, but you have the chance to change the white balance, exposure, contrast, saturation, and even calibration of the red, green, and blue guns or correct for lens abberation – all lossless.
If the white balance is off I have found that it is much easier to fix using the Camera Raw screen than loading the JPEG and manipulating that – the end result is much better as well. The richness, detail (sharpness), color range and ability to adjust these settings end up being so much greater with a Raw file, even though what a Raw file looks like before processing is anything but rich and sharp. As a side note, all of my work that uses creative coloring was colored using the white balance settings in the Camera Raw dialog.
Part of the conversion to JPEG are sharpening algorithms and as a result, the unprocessed Raw file is less sharp. Two things can affect this, one is the brand of camera (Nikon cameras are generally considered sharper, but this is not true across all models) and the other factor is the user settings for sharpening in the camera. Loading a Raw file in a program such as Adobe Photoshop CS2 will automatically apply white balance, sharpening, constrast, brightness, etc… and can even batch process Raw files. I often use this feature as a first pass and then go back and adjust the settings if needed. This is espeacially helpful because even if I did everything correct in camera when I took the photo and my conversion software was able to use the full processing power of my desktop computer, the conversion to JPEG could still trick the camera or my computer and only my eye can produce the correct while balance, constast, brightness, etc…
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