Fw: more on grayscale displays and human vision / camera linearity

[Harry Parker]

Hello Stu,

Sorry for the late reply.  I've been on vacation.
Sounds like an interesting project you are planning.

I wrote the comment on nonlinearity in consumer cameras.  Nonlinearity also exists in most professional cameras and displays. This nonlinearity, often called "gamma", because the fractional power law it approximates is usually written as Intensity raised to a fractional power, written with the Greek letter, Gamma.

Here are some good tutorial starting points. Follow the links!

Gamma FAQ - by Poynton - http://www.poynton.com/GammaFAQ.html
is a good tutorial on the why's and how's of this nonlinearity.
Photometric Calibration of HDR and LDR Cameras - http://www.mpii.mpg.de/resources/hdr/calibration/
Good luck on your project.
--  
Harry Parker  
Senior Systems Engineer  
Dialog Imaging Systems, Inc.

----- Original Message ----
From: Stuart Anderson <[hidden email]>
To: [hidden email]
Sent: Monday, July 17, 2006 9:49:25 AM
Subject: Re: more on grayscale displays and human vision / camera linearity

Colleagues,

Thanks for the wonderful discussion about human vision.  This is fantastic
material for a course I am in the midst of creating entitled Physics for the  
Fine Arts.

I noted in one of these messages (which I can no longer locate) a comment that
cheap video cameras (like the USB webcams one can get for $30-50 these days)
pre-correct for the non-linear nature of human intensity perception that has
been discussed in these exchanges (i.e., would have a logarithmic response?),
while more expensive research cameras are linear (generate signals that are
proportional to the # of photons received).

Since am building some student CCD spectrometers based on a CD and a USB
camera (with frame capture and Image J analysis) to do introductory absorption
spectroscopy this is important to sort out.  I can check the linearity of the
intensity scale from these cameras with ND filters, but if one of you out
there knows about - or recalls the comment about - non-linearity of the
signals from consumer electronics cameras I would love to hear more.

Many  thanks,

Stu
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