Abstract:
A waveform monitor for generating a modified image from an original image includes a brightness measuring system to generate brightness values that are then converted to f-stop equivalents. A selector is used to create a range of f-stop values and a modifier changes the original image for selected pixels that fall within the range of f-stop values. The original image may be modified by replacing or blending certain pixels with colorized pixels, i.e., by falsely coloring the original image. Methods of modifying images in this manner are also described.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional application 61/975,566, entitled F-STOP WEIGHTED WAVEFORM DISPLAY WITH PICTURE MARKERS VIA CURSORS, filed on Apr. 4, 2014, the teachings of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure is directed to a method of displaying information on a monitor, and, more particularly, to an apparatus to monitor a camera output signal waveform, and associated methods of use. 
     BACKGROUND 
     “On-set” or “on-site” video and film production often requires the use of incident and reflected (spot) light-meters to adjust scene lighting and camera gain or aperture. Many times the light-meter measurement and lighting adjustments are done in relative values such as F-stops. F-stops are well known and derive from film exposure and camera aperture or speed adjustment, which is typically adjusted in F-stop increments. The so called F-stop derives from the Focal Ratio or F-number, a dimensionless ratio of focal-length divided by the effective aperture of the camera lens. For example, one f-stop, or “stop”, corresponds to an area increase of 2× or 3 dB in light power but the F-number changes by only sqrt(2). It is typically the F-number that is marked on the lens iris or aperture adjustment. 
     Presently, both film production and video production use electronic imagers within the cameras typically providing a very large dynamic range and adjustable gain (6 dB/stop). For example, according to Wikipedia, film negatives have about 13 stops compared to 14.4 stops for a typical (e.g., Nikon D800) DSLR camera. In video and movie film production, the traditional Gamma (power-law) correction as well as newer log processing within the camera can maintain a large portion of that dynamic range when compressed into a 12-bit or even 10-bit resolution digital video output. It is very important to determine how well that dynamic range is being utilized based on camera adjustment (gain/aperture) and scene lighting. Typically this is done on the camera output signal by viewing the output on a picture monitor (&lt;10 stops of dynamic range). Also note that by simply looking at a well calibrated picture monitor, the dynamic range is limited by the adapted eye to about 7 stops, which leaves invisible detail in the dark portions of the output. A video Waveform Monitor is often also used, but currently these Waveform Monitors are limited to linear voltage indications, with much of the dynamic range near black compressed into just a few mV near 0. Much like the case for analyzing high dynamic range Radio Frequency (RF) signals, a linear waveform scaling is not adequate. 
     Embodiments of the invention address these and other issues in the prior art. 
     SUMMARY OF THE DISCLOSURE 
     Embodiments of the invention include a real-time method and apparatus to monitor the camera output signal waveform with a weighting that provides the combination of removing the gamma or other non-linear correction applied to the camera imager with the conversion of the waveform to a log2, “f-stop”, weighted waveform display with calibrated graticule and cursors. 
     In addition, embodiments include a method and apparatus to allow selection of regions of the calibrated f-stop weighted waveform with adjustable markers or cursors reading out in f-stop values. These adjustable markers preferably provide corresponding indications on a picture display of the regions of the camera image corresponding to the selected f-stop value of the marker. 
     Particular embodiments include a waveform monitor for generating a modified image from an original image include a brightness measuring system to generate brightness values that are then converted to f-stop equivalents. A selector is used to create a range of f-stop values and a modifier changes the original image for selected pixels that fall within the selected range of f-stop values. The original image may be modified by replacing or blending those pixels with colorized pixels, i.e., by falsely coloring the original image. Methods of modifying images in this manner are also described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
         FIG. 1  is a block diagram of an example Video Waveform Monitor including monitor markers according to embodiments of the invention. 
         FIG. 2A  is an example display output of a conventional voltage vs. time waveform. 
         FIG. 2B  is an example display output of a new f-stop vs. time waveform produced by the Waveform Monitor of  FIG. 1 . 
         FIG. 3  is a base image capture used to illustrate embodiments of the invention. 
         FIG. 4  illustrates a traditional voltage waveform for the image of  FIG. 3   
         FIG. 5  illustrates an f-stop waveform for the image of  FIG. 3 , with cursors FSLow and FSHigh, according to embodiments of the invention. 
         FIG. 6  is the image capture of  FIG. 3  that has been modified with color highlighting according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As mentioned above, embodiments of the invention may be used to assess a live video signal from a cameras in terms of relative f-stops (log2 scale) as well as the traditional, linearly displayed, voltage or IRE level. This effectively converts even an analog camera output into a light-meter for relative lighting and exposure in terms of “stops” or “f-stops”. 
       FIG. 1  is a block diagram showing material portions of an example Video Waveform Monitor according to embodiments of the invention. As illustrated in  FIG. 1 , a Waveform Monitor  20  is coupled to and receives input from a camera  12  that is pointed at a subject  14  that is lit by lighting  16 . The camera  12  typically includes adjustments for aperture and exposure index that may be controlled by a camera operator, or the adjustments may be automatically controlled. The camera output is input to the Waveform Monitor  20 . 
     The camera  12  output is first processed by an input processor  30  before passing through a filter  32 , such as a low pass filter, that may be turned on or off by the user, such as through a user interface  50 . The filtered or non-filtered output is fed to a Look Up Table (LUT)  40  that has been loaded with preset tables through the user interface  50 . One portion of the LUT  40 ,  40 A, may be used to remove the gamma or log processing on the luma signal. This process converts the luma signal to a linear light representation. Another portion of the LUT  40 ,  40 B, may be used to convert the luma signal to a Log 2 (Y/Ymax) scale to provide a real-time, f-stop luma signal for a waveform display, such as illustrated in  FIG. 2B . To reduce the size of the LUTs, both mathematical processes are typically multiplied and scaled with high precision before converting to a single set of integer LUT words, thereby eliminating the need for the large word size needed to represent the wide dynamic range of linear light values. 
     There may be multiple LUTs stored in the Waveform Monitor  20 . The user may use the user interface  50  to control which of the stored LUTs is loaded as the active LUT  40 . For example, various LUTs may be pre-stored in the Waveform Monitor  20  that allow user to select the active LUT  40  based on camera gamma and black level. 
     A display monitor  60  on the Waveform Monitor  20  displays output to the user. While the monitor  60  may be used to show the traditional voltage vs. time waveform, such as illustrated in  FIG. 2A , it may also be used to show a new f-stop vs time waveform, such as illustrated in  FIG. 2B . The new f-stop vs time waveform display may use the same user-adjustable cursors as the traditional voltage vs time display, except the output is scaled in “stops” rather than voltage. The horizontal time base is the same for both displays, as illustrated in  FIGS. 2A and 2B , having the conventional selections such as 1-line, 2-line and field sweeps, for example. 
     In addition, a cursor window select block  70  may accept user input from the user interface  50  to read adjustable cursor values set by the user. These adjustable cursor values may be used as binary gate signals to modify an otherwise monochrome output of the Waveform Monitor  20 . More specifically, a color cursor mixer  80  may be coupled to receive the processed input signal from the input processor  30 , or from elsewhere in the Waveform Monitor  20 . The color cursor mixer  80  is also coupled to the cursor window select block  70 . Binary gate signals from the cursor window select block  70  may be used to determine which areas of the original monochrome output will be colored, thus highlighting particular regions of the output, as described below. 
     For example, comparing output  FIGS. 3 and 6 ,  FIG. 3  is an original monochrome output, while the output of  FIG. 6  is the original monochrome picture that has been highlighted in color to identify areas of the picture that fall within the f-stop windows selected by the user. Whereas the image capture shown in  FIG. 3  is a Luma-only or monochrome picture, in  FIG. 6  two color windows are added, for example red and blue, as described in more detail below. 
     To produce the output of  FIG. 6 , with reference back to  FIG. 1 , the log 2 (Y) signal from the LUT  40 , and specifically from the LUT  40 B, is compared with two user controllable window detectors in the control block  70 . Users may control the position and size of cursor “windows”. More specifically, in one embodiment, users may control the center f-stop value as well as the size of the cursor window. The window is used by the system to create binary gate signals. F-stop values from the luma output falling within the specified cursor window are shown on the display as colored pixels, providing information to the user about which pixels in the output fall within the f-stop window. The remaining pixels, i.e., those pixels having brightness levels outside of the specified cursor window from the original image, may be shown on the display without change. 
     Windows may be adjusted in, for example, ¼ stop (f-stop) increments. For example, the window could be pre-configured to plus and minus ¼ stop from the user controllable center f-stop value adjustable over the entire range of the signal from the LUT  40 . In this way, the user can adjust the cursor to highlight any particular region of the picture to determine from the cursor value on the f-stop waveform in  FIG. 2B  or  FIG. 5  the f-stop value, within ¼ stop, of that particular region of the picture as well as other regions with substantially the same f-stop value. 
     The color cursor mixer  80  generates the coloring signals, for example the red and blue pixels for combining with the original image to produce the modified image as illustrated in  FIG. 6 . In one embodiment the color cursor mixer  80  merely replaces the original pixels that fall within the f-stop window with monochromatic red or blue, for instance. In other embodiments the color cursor mixer  80  may generate a blended output by adding a color hue to the underlying luma data. Also, although these examples show a monochrome base image, embodiments of the invention are not limited to luma only, and may be performed in each color channel, for example red, green, blue, independently. 
     In the illustrated embodiment of  FIG. 6 , two colored cursor windows are presented, although more or fewer windows could be produced by the Waveform Monitor  20 . 
       FIG. 4  illustrates the traditional voltage waveform for the image of  FIG. 3 .  FIG. 5 , shows a similar output for the original image of  FIG. 3 , except that  FIG. 5  shows an f-stop waveform for the image of  FIG. 3 , with cursors FSLow and FSHigh, according to embodiments of the invention. 
     Using embodiments of the invention facilitates camera gain/aperture/speed adjustment along with scene lighting in familiar f-stop units, effectively turning the camera into light meter. For example, using embodiments of the invention allow the user to see on a display an F-stop weighted waveform indication with graduated linear scale in stops, such as illustrated in  FIG. 5 . Embodiments also allow the user to measure scene hot spots and lighting uniformity in f-stops with dual cursors, by allowing the user to control delta f-stop difference measurement of picture/scene content elements through both waveform and false colored regions on a monochrome picture display. Embodiments further allow for high resolution black balance indications for camera matching and precise black level adjustment and indication of camera noise. Further, embodiments of the invention provide a tool to the user for scene content dynamic range assessment, to allow for artistic optimization. 
     The Waveform Monitor  20 , or any parts of it, may be embodied in firmware, such as an FPGA, specifically designed circuitry such as an ASIC, or may be implemented by one or more software process running on one or more processors. In other embodiments the Waveform Monitor  20  may include may include a combination of components or operations running on firmware, ASICs, FPGAs, and software, for example. 
     Although specific embodiments of the invention have been illustrated and described for purposes if illustration, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.