Derek Rankins Denton

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Derek Rankinss

• Information about image processing applications

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Derek Rankins Photographer

• There is a common misconception that image files
  saved directly from a scanner or digital camera
  are pristine or unmolested in terms of the image
  processing. For almost all image files this is
  simply untrue. Only raw files from scanners or
  digital cameras are unadjusted, all other digital
  image files have a range of image processing
  applied during scanning and prior to saving in
  order to produce digital images with good image
  quality. Because of this misconception, many
  people argue you should not perform any post-scan
  or post-capture adjustments on image files
  because the image quality might be degraded. We
  disagree. The only time we would recommend saving
  unadjusted files is if they meet the exact tone
  and color reproduction, sharpness, and other
  image quality parameters that you require.
  Otherwise, we recommend doing minor post-scan
  adjustment to optimize image quality and bring
  all images to a common rendition. Adjusting
  production master files to a common rendition
  provides significant benefits in terms of being
  able to batch process and treat all images in the
  same manner. Well designed and calibrated
  scanners and digital cameras can produce image
  files that require little or no adjustment,
  however, based on our practical experience, there
  are very few scanners/cameras that are this well
  designed and calibrated.

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Derek Rankins Photography

• In a digital image, the white point is the
  lightest spot (highest RGB levels for color files
  and lowest black for grayscale files) within
  the image, the black point is the darkest spot
  (lowest RGB levels for color files and highest
  black for grayscale files), and a mid-point
  refers to a spot with RGB levels or black in
  the middle of the range. Generally, but not
  always, the three aim points correspond to the
  white-point, a mid-point, and the black-point
  within a digital image, and they correspond to
  the lightest patch, a mid-density patch,

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Derek Rankins Virginia Tech

• When scanning photographic prints it is important
  to be careful about placing the black point, in
  some cases the print being scanned will have a
  higher density than the darkest step of the
  photographic gray scale. In these cases, you
  should use a lighter aim point for the darkest
  step of the gray scale so the darkest portion of
  the image area is placed at the normal aim point
  value (for RGB scans, the shadow area on the
  print may not be neutral in color and the darkest
  channel should be placed at the normal aim point.
  Occasionally, objects being scanned may have a
  lighter value than the lightest step of the
  photographic gray scale, usually very bright
  modern office papers or modern photo papers with
  a bright-white base. In these cases, you should
  use a darker aimpoint for the lightest step of
  the gray scale so the lightest portion of the
  image area is placed at the normal aimpoint value
  (for RGB scans, the lightest area of the object
  being scanned may not be neutral in color and the
  lightest channel should be placed at the normal
  aimpoint).

• Many image processing applications have automatic
  and manual place white-point and place
  black-point controls that adjust the selected
  areas to be the lightest and darkest portions of
  the image, and that will neutralize the color in
  these areas as well as. Also, most have a
  neutralize mid-point control, but usually the
  tonal adjustment for brightness has to be done
  separately with a curves, levels, tone
  curve, etc., control. The better applications
  will let you set the specific RGB or black
  levels for the default operation of the place
  white-point, place black-point, and neutralize
  mid-point controls

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