Creating Video Looks Using Camcorder Image Adjustments
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JVC GYHM 850 camcorder provides ample adjustments to create custom "looks".
Some who shoot RAW using a digital cinema camera claim those who shoot with a video camcorder must live with the camera’s built-in look—a look designed by engineers in Japan. They also claim when you shoot with a digital cinema camera, during color grading you are able to “design your own camera.” However, today’s camcorders provide a wealth of adjustments, which can create almost any desired “look”.
What’s omitted from their argument is that professional camcorders have for decades supported a large set of image adjustments. True not all shooters use these options, but that doesn’t negate their availability. In fact, those now learning to color grade with, for example, DaVinci Resolve will gain color science knowledge they can use to make better in-camera image adjustments. (Learn about Resolve at: Grading With DaVinci Resolve 11.3, Part 3 of a Series and Grading With DaVinci Resolve 11.3, Part 4 of a Series.
We will examine four types of image adjustment you can use to obtain the look you want from a camcorder: Dynamic Range control, Sharpness control, Color Matrix control, and Gamma control.
Dynamic Range Control
To increase a camcorder’s dynamic range, a circuit can be employed that disproportionately decreases signal level as brightness increases over a certain level. This circuit prevents bright details from going fully white, thus losing both detail and color.
The circuit has a response curve with two segments—a segment beginning at 0-percent and a second segment that typically begins around 80-percent. The curve’s break point is its knee. The second segment compresses levels between the knee and 108-percent. Figure 1 shows a low-knee curve that can provide 2-stops of additional dynamic range.
Figure 1: Low-knee setting can increase dynamic range
Figure 2 shows a high-knee gamma curve. With the knee up around 95-percent, upper-middle shades are made brighter.
Figure 2: High-knee setting increase the brightness of light colored detail
The desired knee-point can be set manually. Alternately, an automatic knee can be engaged to dynamically set the knee based upon the range of light within a scene. When the range is large, the knee is moved lower. When the range is small, the knee is moved higher.
Sharpness Control
Edge enhancement, also called aperture correction, is adjusted by the camcorder’s Sharpness control.
- Sharpness— alters both horizontal and vertical edges.
- Vertical Sharpness—alters the edges of horizontal lines.
- Horizontal Sharpness—alters the edges of vertical lines.
Figure 3 shows three correction settings where “8” is the default (Normal) setting. Note that no matter the setting, as detail resolution moves over the 50-percent point, the amount of correction becomes progressively less. Aperture correction, therefore, has a limited ability to enhance fine detail. The Sharpness adjustment primarily has an effect on the edges of objects.
Figure 3: Aperture correction can increase or decrease image sharpness
Figure 4 is a BBC diagram showing a transition from gray-to-white and a white-through-gray-to-black transition. When the start and end of a step are rounded (Sharpness setting of “1”), object edges will be very soft. (The “4” setting in Figure 2.) Conversely, at a Sharpness setting of “16,” each step begins with an overshoot to excessive white or black. This overshoot is called ringing. (The “12” setting in Figure 2.) While ringing does make object edges more distinct, unfortunately the overemphasized edges increase the visibility of motion judder from low frame-rate video.
Figure 4: Sharpness control can decrease or increase edge visibility
Color Matrix Control
We know camera manufacturers tend to create cameras that have a look similar to other cameras they produce. 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 whites appear to look very clean. The downside are green tree leaves that look less lush.
A camera’s factory defined colorimetry is determined by its color matrix. You can, however, adjust the matrix to:
- Match multiple cameras of the same type
- Match multiple cameras of different types
- Emulate another video camera’s look
- Emulate a film emulsion
Simply put, a color matrix defines the look of the primary colors. For each color in the matrix, Red for example, there will be a Saturation adjustment and a Phase (hue) adjustment.
Because adjusting a matrix is complicated, camcorders provide a set color presets. The Standard matrix provides the saturated colors associated with video. See Figure 5.
Figure 5: Standard/Normal color preset
A Cine preset, as shown by Figure 6, provides far less saturated colors.
Figure 6: Cine color preset
Some camcorders also provide the ability to redefine a preset. Thus one can decrease or increase the Red saturation of the Cine preset. See Figures 7 and 8.
Figure 7: Red saturation set to minimum—Red and Cyan saturation are reduced
Figure 8: Red saturation set to maximum—Red and Cyan saturation are increased
Phase (0- to 259-degrees starting at 3 o’clock) may also be adjusted. Figures 9 and 10 show Red phase adjusted clockwise (phase-angle increased) and counter-clockwise (phase-angle decreased), respectively.
Figure 9: Red phase-angle increased—Red hue shifts clockwise toward Blue
Figure 10: Red phase-angle decreased—Red hue shifts counter-clockwise toward Green
Gamma Control
Gamma is the relation between input (X-axis) and output (Y-axis). The relation can be represented by a curve. Figures 11, 12, and 13 present simulated gamma curves. (Rightmost curve of the four graphs.)
Figure 11: Linear gamma curve—no signal alteration prior to applying REC.709 gamma
Figure 12: Curve bows below linear—mid-shades pushed darker increasing apparent contrast
Figure 13: Curve bows above linear—mid-shades pushed brighter decreasing apparent contrast
Non-simulated gamma curves look very different. Nevertheless they express the relation between input and output. Figure 14 presents three gamma curves: Normal/Standard plus two Cine curves. You select the gamma curve that creates the look you want.
Figure 14: In-camera gamma options
Normal gamma is designed for shooting video. Cine gamma curves are designed to record with less image contrast so material looks less like video. Many camcorders, in addition to a selection of gamma options, provide one or more image presets such as Black Stretch.
Video, relative to film, has a limited dynamic range. In a high contrast-ratio scene when the lens aperture is adjusted so bright details are not overexposed, shadow detail will disappear into black. The Black Stretch preset raises the lower end of the gamma curve. This has the effect of making shadow detail lighter so it is more visible. See Figure 15.
Figure 15: Black Stretch—histogram shows “blacks” shifted right increasing shadow detail
By employing available camcorder adjustments, you can record video that has the look you want. Moreover, defining an in-camera look does not preclude post-production color correction.