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RAW image format

RAW is simply pixel data as it comes directly off the CCD, no in-camera processing is performed. Typically this data is 8, 10 or 12 bits per pixel. The advantage being that file sizes are considerably smaller than an equivalent TIFF file. The image has not been processed or white balanced which means you can correct the image, and it's a better representation of the "digital negative" captured. The disadvantage is you can't open these image files with a normal photo package, in the case of Minolta RAW files (.MRW) you must use the Minolta DiMAGE Viewer.

A little background: each pixel of a CCD can only see one colour, depending on the CFA (colour filter array) placed over the CCD this is either Red/Green/Blue or Cyan/Magenta/Green/Yellow. The cameras internal image processing engine then interpolates colours from the value of neighbouring pixels to calculate a full 24-bit colour for each pixel.

What's slightly odd about Minolta's MRW format are the size of the image files. The DiMAGE 7i uses the Sony ICX 282 CCD sensor which outputs 2588 x 1960 effective pixels (some are lost in the de-mosaic process). Minolta report the camera has having a 12-bit A/D converter. Thus MRW RAW files should be approximately 7,430 KB (less header). However, MRW files come out of the camera approximately 30% larger at 9,741 KB. I have no idea where this extra overhead comes from but it does slightly reduce the usefulness of Minolta's RAW format.

Minolta DiMAGE Viewer

DiMAGE Viewer is the supplied image browsing / conversion application. It allows you to browse, view and organize images from the camera. It also provides the ability to convert RAW files (.MRW extension) to JPEG, TIFF or BMP. Double-click on a MRW file in the DiMAGE Viewer browser window and you will see the options dialog shown below.

This RAW file dialog allows you to change any of the following parameters:

  • Color Mode (Color / B&W)
  • White Balance (Camera, Daylight, Cloudy, Tungsten, Fluorescent, Manual from image, Kelvin temp)
  • Filter (-3 to +3)
  • Saturation (-3 to +3)
  • Contrast (-3 to +3)
  • Sharpness (Soft, Normal, Hard)

The only setting we normally see which is unfortunately missing is digital exposure compensation, it would be nice to have this option because it is one of the most useful features of RAW files. A group of settings can be saved as a 'RAW Job' and retrieved later when converting another image.

RAW vs. JPEG (Scene)

RAW (.MRW) (click below for re-saved JPEG) JPEG FINE (.JPG)

RAW vs. JPEG (Resolution)


Although the RAW resolution chart does look a little better than the JPEG version (less moiré, less sharpening artifacts) a closer inspection shows that DiMAGE Viewer's Bayer interpolation algorithm is introducing some very strange dot artifacts along diagonals:

These are also visible in the scene shot from above:

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