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Wednesday, March 30, 2011

On the Importance of Raw

  All high end cameras and some consumer cameras offer to give you your pictures in either Raw or Jpeg format (or sometimes both).    Raw format is simply the data off the sensor whereas jpeg format is the result of transforming that data into a image and compressing it in a lossy way.

  The conversion from Raw to Jpeg is not trivial.  A digital pictures is a rectangular grid of pixels, each pixel being an intensity value for Red, Green and Blue.
  • The camera's sensor only records the intensity of one color at each pixel location.   The intensity of the other two colors must be determined from neighboring pixels.    
  • The camera must determine the color of the light that illuminated the scene and then transform all the color values so that white objects appear white in the Jpeg and other objects appear their correct color.
  • The image must be sharpened. 

 The camera's computer does all this computation very quickly.  Usually it takes less than a second to create a Jpeg from the sensor values.   The alternative way to create a Jpeg is to take the Raw file from the camera and run it through software provided by the camera manufacturer.   For my D7000 it takes about 30 seconds to convert a Raw file to a Jpeg file.  That is 30 seconds running on a very fast cpu that's many times more powerful than a camera's computer.

The question is often raised: should I shoot Jpeg or Raw? 

Well, the in-camera Jpeg is produced in one second on a weak processor, and the Jpeg from the Raw will take 30 seconds to create on a very powerful machine.

 Put that way which Jpeg do you think is better?

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