David Esp Video Technical Blog

To obtain/maintain/increase/verify an intuitive feel and hence greater confidence for the appropriate use of gamma in camera settings, I did some thinking & research.  The basic idea is as follows:

• A typical consumer camcorder produces crisp images
• “Film Look” use of a professional camera may employ non-standard gamma settings in the camera settings.
• The straight results of this are images of “washed-out” appearance.  To obtain a pleasing result requires grading (levels & gamma, saturation, color curves etc.).  Example: http://reduser.net/forum/showpost.php?p=687243

Regarding the second, more professional approach:

• The immediate result is “scary” because it looks washed-out
• The goal is not to produce an immediately-pleasing image but to capture “as much information as possible” (an often-quoted phrase) from a scene, with the intention and indeed requirement for grading.  One has to see it “through the eyes of a grader”.  A naive person (e.g. a newbie or a client) will of course not immediately see it that way.
  • Example references to this:
    • http://www.dvxuser.com/V6/showthread.php?232389-The-Red-quot-LOOK-quot
      • <<The RED RAW look, the washed out, flat, low contrast, incredibly versatile form in which the footage originates … screams possibility in our faces. Low contrast can, to the DP, imply power … being precious with the RED footage, and trying hard to save every bit of detail we started with.>>
      • <<I can see how the washed out look can become something in and of itself, and have people like it, and others not.>>
• What does this mean?  In general, possibly:
  • The complete levels and color space of that scene, un-clipped (clipping destroys information).
  • Any subtle light/shade within shadows of the scene.
• Questionable aspects:
  • Grading takes time (bad for quick-turnaround jobs) and if written to intermediate files (e.g. prior to editing) then it can also eat disk space.
  • There is a trade-off between generality and specificness.
    • Capturing maximum information provides the grader with greatest freedom.
    • On the other hand if it is known in advance that crushed shadows are required, e.g. to obtain silhouettes / film noir effects, then it is a waste of effort / bits if not counter-productive to boost them in the camera.
  • The degree to which grading can be applied in practice depends on the levels and color space resolution of the camera.
    • Prosumer cameras such as Z1 or XDCAM-EX record to 8-bit levels resolution.   And then only a sub-part of that levels-space (typically 16..255 or 16..235, depending on camera and settings).
      • For cameras whose sensors work at greater resolution (and can output this information) there is the option to record to external devices at that greater resolution (e.g. 10 bits 4:2:2).
    • While it is possible to apply effects like levels, gamma or color-curves (S-curves) to “professional” washed-out imagery, beyond a certain degree, the image will appear ragged or flesh-tones will appear sunburn etc., as the gaps between successive values of the bit-space get stretched too big.  One can actually see the gaps (between striations) in a Waveform Monitor (applied to the result of grading).
      • In that case we have in fact lost information, defeating the original goal…
    • If the results of grading are pretty-much identical (or, from the previous point, possibly inferior) to what would have been obtained in-camera using a more standard setting, then what was the point?
• Reassessment:
  • Due to the trade-off issues, the real goal should be to record the maximum relevant information.   In other words, to be a little bit specialised.
    • This is the logic behind employing physical filters on a camera, such as grad filters (“sunglasses” e.g. for the upper – sky – part of the image).
    • Even on feature movie sets I have come across formal instructions for film cameras to be deliberately “pushed a stop or two”.  Committing at record-time to something that could, presumably, have been achieved equally-well in post, which itself can be done almost immediately based on HD footage recorded simultaneously from HD cameras attached to the main camera.  I have seen directors receive rushes and quick cuts from such cameras within seconds…
  • The degree of commitment/specialization may depend on the type or uncertainty of the scene and on the consequence of making a mistake.  Feature films are very planned and their shooting is very iterative.  On the other hand there can be one-offs such as special-effects or VIP moments.  At the other extreme may be live events where anything can  happen – subjects, lighting, over-bright/over-dark etc.
  • The missing factors in the “maximum information” principle are then:
    • Relevance – what kinds of information are relevant?
    • Resolution limitations.
      • If we only have 8 bits, then what is the practical limit of grading?
      • Conversely, if we need to maintain maximum latitude etc., when do we need more than 8 bits (in practice mostly 10 bits)?

This entry was posted on Sunday, February 20th, 2011 at 12:17 and is filed under gamma, grading, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.