• Contact
• SMPTE.org

• About
• Attend
• Exhibit
• Schedule
• Sessions
• Sponsors
• Media
• Partners

Exhibit Hall Open

Grand Ballroom Salons 3-6

Tuesday 1:00 pm- 7:00 pm
Wednesday 10:00 am- 5:00 pm
Thursday 10:00 am- 2:00 pm

Proposal for practical screen luminance uniformity measurement

François Helt (Doremi, France)

Screen luminance uniformity measurements in Digital Cinema specifications are following a well known pattern applied since a long time. Traditional method to evaluate screen luminance uniformity is based on measurements at positions defined by a 3 x 3 grid dividing the screen in equal areas. It can be easily shown that this does not prevent unsatisfactory lighting conditions. In fact off-center hot point and abrupt luminance discontinuities may stay unnoticed by the measurement method. Increasing the number of measurement position is not the answer. A method is proposed to characterize a screen uniformity which could give satisfactory projection comfort in all circumstances and would allow precise measurements protocols. A projection system for large screens exhibits always a brighter zone with decreasing intensity farther away in all direction. This is due to a phenomenon called vignetting. • natural vignetting law for lens systems (cosine to the fourth power) which varies in function of projection angle • vignetting caused by baffling systems (optical path obstacles) In order to evaluate non uniformities we are using mathematical models to describe various projection intensity profiles • simplest vignetting combination: three parameters (vignetting rates for red green and blue) • off-center vignetting: five parameters (vignetting rates for red green and blue plus horizontal and vertical center displacement) A simple physical model for a projection system could be used in order to check and develop further the mathematical model: • lighting and imaging system (this apparatus is likely to give complex profile) • projection lens (the vignetting of a good lens is simple and centered) We derive a more sophisticated uniformity model based on combination of: • an off-center vignetting model caused by lighting and imaging path • combined with a centered vignetting caused by the lens system. How to do measurements based on these models and how to specify and measure the tolerances.
 

Wednesday, Oct 28
8:30 AM - 11:00 AM

Sponsors