Shedding Light on HyperGamma
September 9, 2009
I recently had breakfast with an acquaintance from college who is now a cinematographer. He and I have always done friendly sparring since he went to work in the big screen industry and I went to work in the small screen industry.
This time our breakfast took on a different tone as we were both lamenting our respective industries' transitions to digital technology. The transition paths have been rocky and both of us have seen what we believe are compromises to the quality of the end products for the sake of saving dollars. We have both gone through the agony of a budget cut or staff reduction based on capabilities of new technologies that are finally realized after a year or two of waiting for the software developers to catch up with marketing and sales. In the lag between promised benefits and delivered capabilities, shrunken staffs are forced to do more with less. It is no wonder we lament how things have progressed.
It was in that context we started discussing digital camcorders and CCD cameras in general. Since CCD cameras and digital recording have been deployed longer and more widely in television then in the movies, most of the "problems" have been dealt with. I had my first experience with CCD cameras when I had to replace three ancient RCA TK-44's with three Sony BVP-7A's while I was at KHON in Honolulu. It was great to be able to tell that news anchor Joe Moore was actually wearing a pastel colored shirt because the BVP-7's didn't clip the chroma and make everything pastel look white. Of course the true tests for any camera on a news set are the sports anchors who always show up in a sports jacket with a hideous pattern/color combination. That's when we discovered that we had traded moiré for fix pattern noise.
|HyperGamma, a feature in the Sony PDW-700 camcorder, provides a set of correction curves that allow for more accurate color representation and tracking within images that have wide dynamic range. The screengrab on the left depicts a scene before selecting HyperGamma, on the right, after HyperGamma has been applied. |
As I implied above, in the 20 plus years since, a whole lot of progress has been made. I was glad to be able to share my experiences up to and including our most recent purchases at Iowa Public Television, which included 11 Sony HDC-1550's—five configured for use in our studios and another six that are used on our HD remote truck—as well as four Sony PDW-700 XDCAM camcorders for field production.
We really started comparing notes on the PDW-700's and the PDW-F800 that he is considering. Since the PDW-F800 is an extension of the PDW-700 he was hopeful that I could offer some assistance. Not being a videographer, I could only relate some of the anecdotal comments from conversations I have been part of regarding the camera's operation and strengths. I was comfortable talking about the benefits of the 2/3-inch imagers being able to actually capture 1920x1080 rather than the 1440x1080 that was the standard with 1/2 inch imagers. I also know that our folks like the Blu-ray media format not only for its ease of use but also because it is a cost-effective medium.
It was when he asked me about "HyperGamma" that I was at a loss. Somewhere in the past I remember reading something about HyperGamma but it was related to Sony's CineAlta line of cameras and I didn't really look at it all that carefully. My friend noted that he thought HyperGamma was a feature in the PDW-700. I told him that it might be but I was not at all familiar with it or what it did. I was so curious about it I started to do some research and discovered that HyperGamma is indeed a feature of the PDW-700 but on some early models it required a firmware update. I had to check with folks back at the station to see if we had the right firmware and as it turns out, we do.
So what is HyperGamma? In its simplest terms, it is a set of correction curves that allow for more accurate color representation and tracking within images that have wide dynamic range. In the standard video camera we typically adjust the camera knee point and knee slope for the best compromise between light level performance and color tracking but even at its best, we have all seen people's skin tone shift in color as the overall light available changes or on an outdoor shoot as clouds cross the sun or in a darker scene where mobile light sources move in and out of frame. The reason for this is the wide frequency response across the color spectrum causes the image circuitry within the camera to respond differently based on the color/luminance relationship. Within reason, adjusting the knee point and slope can restore the proper relationships but the adjustments would need to be made continually and would still result in unsatisfactory performance because in many cases, the fight to keep the color true would result in loss of details in low and high luminance areas of the frame. The HyperGamma curves incorporated into the PDW-700 allow the operator to pretty quickly select an intelligent performance curve best suited for the conditions at the shoot and the look desired.
This type of control has always been a big deal within the film industry as cinematographers are virtually always shaping the look of the final content. They have done this through the use of optical physics with lens selection and lighting and with chemistry through film selection and processing. With over a century of film making history behind them, the techniques and processes are pretty well understood.
With video cameras starting to make their way into film production there needs to be ways to allow for similar types of control and HyperGamma is one of the tools. This wasn't such a big deal for broadcasters in part because our final product typically ended up on a television screen with less than stellar resolution, and bad lighting after traversing a number of modulation and demodulation cycles pretty much removed any of the subtle and some of the not-so-subtle shortcomings of inaccurate image reproduction.
But now everything is digital, including the home display. It may still be in a poorly lit room but it is bigger than it used to be and it has a dynamic range that really shows off the subtle qualities of the images. It may therefore be in the broadcasters' best interest to take the steps necessary to ensure that the images they create (even for news and local commercials) are at a high enough quality to fit well between the cinematic content that they air.
Bill Hayes is director of engineering for Iowa Public Television. He can be reached via TV Technology.