For over 50 years, Hitachi Kokusai broadcasting and production camera systems have delivered high-performance image acquisition for demanding live and recorded events.
Today’s fully digital system cameras provide a wealth of image adjustments. While most users can simply choose between multiple preset “looks” that are included in the camera, other users may want to tailor these settings to address specific characteristics of their shooting environments or for creative preferences.
Using a waveform monitor (WFM) and vectorscope – either as standalone devices or built into professional video monitors – can increase the accuracy of adjustments you make with the numerous controls available through modern digital processing.
To begin “shading” the camera, start by making a good black-and-white (luminance) picture. The best way is to use a standard Grey Scale or “Chip Chart.” In Figure 1 is the Chip Chart, with the resulting WFM display of a correct B&W adjustment shown in Figure 2.
Figure 1: A grey scale or chip chart
Following the B&W luminance adjustment, you can begin to “paint” the camera by adjusting color hues and saturation. You can paint to your own preference or use a particular chroma preset by using a vectorscope.
Figure 2: A correct waveform monitor (WFM) display.
An experienced camera operator can make these “shading” adjustments on the fly during a live or recorded event to achieve an excellent picture and avoid needing extra time and expense in post-production. In addition, “riding” the lens iris and black levels may be required during a live event to accommodate changing conditions.
In addition to the aforementioned “shading” and “painting,” many other types of image adjustments are available in system cameras. Four of the most commonly used are:
• Gamma correction
• Dynamic range and HDR
• Sharpness and detail adjustments
• Color Matrix control
The next sections will provide an overview of each of these functions.
Gamma Correction
Gamma, which is represented as a curve, defines the relationship between an input signal value and output display brightness. From a technical perspective, gamma correction is used to adjust for the differences between how a camera acquires an image, the way a display system presents that image, and the way the human visual system perceives the result. In practice, gamma correction can adjust the overall perceived brightness of an image without washing it out or darkening it entirely.
The gamma curve used within a camera is typically intended to be the inverse of the gamma curve of the display, thus combining to form a “system gamma” curve that enables the image to be perceived accurately. You can select or adjust the camera gamma curve to create the look you want.
Figure 3: System Gamma Curve (in red)
Normal gamma (ITU-R BT.709) is designed for shooting HD video. The original CRT display had a characteristic curve that was standardized as BT.1886. While CRTs are gone, today’s flat panel displays still use this curve. The camera’s standard gamma curve, shown in blue, is the approximate inverse of the display curve.
Dynamic Range Control and HDR
“Dynamic range” refers to the difference between the blackest black and brightest white that can be captured by a camera and shown on a video display.
Figure 4: A comparison of knee settings
Knee Settings
To increase a camera’s standard dynamic range (SDR), a “knee” curve can be employed that disproportionately decreases the video level as brightness increases over a certain point. This prevents bright details from “clipping” and losing both detail and color. The circuit has a response curve with two segments—a segment beginning at zero percent and a second segment that typically begins around 80 percent. The curve’s break point is its “knee,” and the second segment compresses levels between the knee and 100%.
Figure 4 shows a low-knee curve (in yellow) that can provide two stops of additional dynamic range. A high-knee setting (in purple) increases the brightness of mid-range and above, allowing the signal to reach higher levels with less knee curve. The desired knee point can be set manually. Alternatively, an automatic knee can be used to dynamically set the knee based on the scene: the knee is moved lower when the dynamic range is large or moved higher when the range is small.
Black Stretch
When the lens iris is adjusted so bright details are not overexposed, shadow detail may be crushed into black. The Black Stretch adjustment raises the lower end of the gamma curve, which has the effect of making shadow details more visible.
High Dynamic Range (HDR)
HDR brings a long-overdue improvement to video experiences. HDR enhances cameras’ gamma curves and peak brightness, and most professional broadcast cameras can output HDR signals. However, until recently, the impact of HDR was limited by the peak brightness capability of flat-panel TV displays. As these displays have gradually increased their brightness from 100 nits to over 1000 nits, HDR peak brightness is now possible. You can learn more about HDR in our earlier article “Enhancing Your IMAG with HDR.”
Sharpness Control
“Edge enhancement,” “detail,” and “aperture correction” are all terms that are used to describe ways of adjusting the camera’s apparent sharpness.
The higher the contrast in an image, the sharper it appears. This is one reason why HDR pictures appear to be sharper. “Detail” enhances lower-frequency transitions from light to dark in the picture by exaggerating the transition with the addition of a black or white edge. You can adjust the ratio of horizontal and vertical correction; the maximum brightness or darkness of the applied edges (white and black limit); the thickness of the edges (frequency); and the minimum contrast change that the correction will be applied to (crispening). You can also tell the camera not to apply detail correction to dark areas (this is known as “level depend”).
Fine details and textures are normally represented by high frequencies within the image. Aperture correction is a simple high-frequency boost that compensates for the natural fall-off in camera lenses at higher frequencies. This helps enhance transitions from dark to light or light to dark in fine detail and textures like fabrics, skin, hair, or grass within the image.
Skin Tone Detail
To maintain or even improve the youthful look of faces, special processing can automatically or manually detect the skin tone color vector and apply a detail reduction. This reduction in detail has the effect of smoothing out complexions. Only the skin color vector is softened, so eyes, hair, lips, and teeth remain unchanged. The skin tone color vector is very similar for all skin complexions, as luminance level is the primary difference between complexions. The Skin Tone Detail level can be also adjusted to follow the lens zoom position to provide a more natural overall look for your talent in wide angle shots.
Color Matrix Control
Figure 5: Vectorscope display of properly adjusted SMPTE color bars
Manufacturers create cameras that capture video with a “look” similar to the other cameras they offer. Some brands have a cooler look while other brands have a warmer look. Green, for example, may be defined by a design team to be slightly bluish so that whites appear to look very clean. The downside in this example is that green tree leaves or grass may look less lush.
A camera’s factory-defined colorimetry is determined by its color matrix. You can adjust the color matrix to match multiple cameras of the same type; match multiple cameras of different types; or emulate another camera’s look.
Figure 6: SMPTE color bars
Simply put, a color matrix defines the look of the primary colors. For each color in the matrix (e.g., red), there is a Saturation adjustment and a Phase (hue) adjustment. Because adjusting a matrix is complicated, cameras provide color presets. The Standard matrix provides the saturated colors associated with video.
Putting You in Control
By employing available camera adjustments, you can capture video that has the look you want. Of course, defining an in-camera look does not preclude post-production color correction, but it’s essential for live productions and can save time and effort in the post process.
Hitachi professional camera systems give users deep control of all of the adjustments described above plus many more. Check out the Tech Tips videos on the Hitachi Kokusai Electric America website to see how to access some of these settings on Hitachi cameras, and keep an eye on our new “Production in Focus” blog for more informative insights.
