Quality Control in Digital Cinematography John Galt Senior Vice - - PDF document

Quality Control in Digital Cinematography

John Galt Senior Vice President, Advanced Digital Imaging, Panavision The photo-chemistry involved in the manufacture and processing of silver halide film emulsions has always required careful process control. Inherent in the technology has been the requirement for quality control at every stage from negative manufacture to chemical development of camera negative, intermediate film elements, through final release printing. Over the past 100 years of the evolution of this technology a close collaboration between the film manufacturers, the film laboratories, and the end users, has evolved to the point where this process is almost taken for granted and although various problems can and do arise, the system has evolved to where problems are usually quickly identified and remedied. Mainly through television broadcasting, electronic motion imaging technology has been a major part of our entertainment and information systems for more than half a century. Yet, it has been less than a decade since electronic imaging systems have been developed that rival the image quality of the silver halide-based motion picture film technology first developed over a century ago. The vigilant quality control process that we take for granted in film-based imaging systems must now be re-invented to encompass the new world of digital image capture, post production and archiving. This paper will explore the various issues and problems involved in developing an adequate quality control process for this nascent technology. Today the majority of major feature films and all filmed television will be digitized at some point in their life cycle. In addition to the digitizing of film elements, increasingly we are seeing television programs and indeed major feature motion pictures being photographed with a variety of electronic imaging cameras. [PHOTO OF HDW-F900] This is a photograph of the camera used by George Lucas to photograph episode 2 of the second STARWARS trilogy. This camera used three 2 million pixel CCDs or Charge Coupled Devices for a total pixel count of 6.2 mega-pixels. Although the pixel count is quite adequate to produce a high quality image on a cinema sized screen the sensor size is only 9.6 x 5.4 millimeters with an 11 mm image diagonal much smaller than super 16 motion picture

• film. Because of the aesthetic photographic limitations of this format very few major features
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have been photographed with this camera. However, it has had a long and illustrious career in television sitcoms, drama, and documentaries. [COMPARISON OF 2/3” AND SUPER 35] [PHOTO OF GENESIS] This is Genesis, the first electronic-cinematography camera to break through into the major feature market. To date, this camera has been used as the principal camera system on over 40 feature films throughout the world. This camera utilizes a single 12.4 mega-pixel CCD the same size as a “D” format Super 35 film image and therefore can use any of the thousands of lens types we have developed over the last 50 years for 35 mm film cameras. [PHOTO OF GENESIS with PANAFLEX] [PHOTO OF GENESIS SENSOR AND SUPER 35 FILM] [GENESIS SENSOR DIAGRAM] Both of these cameras utilize what is known as area array sensors consisting of rows and columns of photo-sensitive diodes more commonly called pixels. In operation, these cameras use an electronic shutter that “opens” to begin the exposure. During the exposure time, photons striking the individual photodiodes build an electric charge that is proportional to the quantity of incident light striking the pixel and at the end of the exposure time the shutter “closes” and the charge is transferred off the sensor in preparation for the next exposure. The most important thing to understand about this process is that, unlike motion picture film, the same imager is being exposed over and over again, and therefore any flaw in the imager will be on all the images from that camera. It is important to realize that this same technology is used in devices such as telecines, film scanners and other types of film digitizers and therefore the same kinds of problems that can

• ccur in camera original images can also be present on digitized film images. Of course, if a

problem is detected in a digitized film image a simple though possibly expensive solution would be to re-digitize the film. In the case of a camera original, it is either re-shoot or fix the image. Before examining the some of the problems that can occur with digital imaging it might be useful to examine what is routinely done to repair problems in film images.

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[BIG HEAT 1] This frame of film shows obvious and extensive damage, yet because the damage on this frame does not exist on the previous frame, [BIG HEAT 2]

• r the next frame.

[BIG HEAT 3] Although they too have damage it is in a different parts of the frame, and we are able to utilize local information from each of these frames to effect a repair to the other. [BIG HEAT 4] Most problems we see in film images are localized such that we can use previous or next frame information to enable a repair. The problems that can occur with area array or line array CCD or CMOS imagers almost seem trivial compared to the kind of damage that motion picture film is sometimes subjected to. However, as stated previously, any anomalies will persist throughout the sequence, or possible all the material, shot or scanned with that particular sensor. [CCD CHARGE TRANSFER] This diagram is a much simplified diagram of how an interline transfer CCD like that used in the Genesis camera works. Although rare, there are many problems that can occur in digital imaging devices. The most common of which is dirt on the sensor. Any user of interchangeable lens digital still cameras will be aware of this problem. An individual still image is easily fixed in image processing software such as Adobe Photoshop™. However, a minute of images from an electronic cinematography camera contains 1440 images that need to be fixed. Gensesis has a sealed cavity to deal with this problem, but since a pixel is only 4 microns a dirt particle less than one twentieth the thickness of a dollar bill could obscure a pixel. What follows is a series of images that illustrate some of the problems we have encountered and information about a strategy that we are evolving into a hardware product that can be used

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in a post-production environment or Q.C. process that can assist in discovering potential problems. The purpose of this presentation was not to provide a litany of all the possible problems that can occur. That would probably only serve to terrify us all and I should emphasize that most of the problems we encounter are quite rare. My hope is that to the degree that you can you will influence others to return to the ancient but tried and true practice of viewing camera dailies at the highest possible resolution. You may feel that you are too far removed from the origination process of the images to have much influence in this area but the reality is that most of the most egregious problems that I see come to light only during the post production Q.C. process. This is usually long after the production is finished and this is definitely the most expensive time to fix problems.

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