Project Development


raw-file-format-symbolWhen first I dipped my toes into the waters of stained glass window photography, through habit, I captured the images in JPEG format which is inherent with problems that work in antagonism with image quality.  At its most basic level, JPEG is a ‘lossy’ format – every time a file is saved, image quality is sacrificed. By contrast, RAW can be lossless.

More significantly, the improved handling of Dynamic Range makes capture in RAW format eminently more sensible for stained glass windows, which are notorious for having a very high dynamic range.  RAW allows the post production flexibility to darken (burn) the highlights while raising (dodging) the shadows. It is possible to tone-map an image appropriately in a process far more akin to analogue work in a darkroom.

Shooting in RAW raises an exciting prospect for this project: might it be possible to achieve the same results with a single RAW file that previously required a series of six exposure bracketed JPEG files?  If not, I suspect there could be a reduction in the number of exposure bracketed RAW files compared with JPEG files.

RAW key advantages for this project:

Increased dynamic range:  RAW files contain a greater dynamic range – the ratio between the maximum and minimum measurable light intensities (white and black, respectively).

Increased Colour Depth:  JPEG is captured in 8-bit, RAW can be captured in 12-bit or 14-bit

  • 8-bit means 28 tonal values (256) for each colour (red, green, and blue) per pixel (16,777,216 unique colours)
  • 12-bit means 212 tonal values (4,096) for each colour (red, green, and blue) per pixel (68,719,476,736 unique colours)
  • 14-bit means 214 tonal values (16,384) for each colour (red, green, and blue) per pixel (4,398,046,511,104 unique colours)

What can the human eye see?  It is worth highlighting the fact that the human eye is unlikely to be able to discern all the colours in an 8-bit image, so shooting at 14-bit may seem nonsensical. When discussing the number of colours perceptible to the human eye, wisdom tends to refer to the 2.4 million colours of the CIE 1931 XYZ colour space.  This is based upon sound scientific evidence, but might be rather limited by context.  When referring to both chromaticity and luminosity it may be possible for the human eye to be sensitive to 10-100 million distinct colours.

Raw files are the equivalent of negatives:  A RAW file is the image data exactly as captured on the sensor. Any settings you apply in white balance, Picture Styles and some other areas are only appended to the image as a small header file. This means they can be changed later in RAW conversion software such as Canon’s Digital Photo Professional.  The RAW file is an original record of what was ‘seen’ by the camera.

RAW format disadvantages:  Pleasingly, none of the main disadvantages in using the RAW format are a concern in the photography of stained glass:

  • RAW file require post-processing
  • File sizes are considerably larger
  • Fills up the buffer more quickly (however, the EOS-1D X Mark II achieves a maximum burst rate of up to 170 full-size RAW files)
  • It is a propriety format (Canon RAW files are .CR2, Nikon RAW files are .NEF)


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