Patent Publication Number: US-2023139880-A1

Title: System to display gamut excursion

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 to Indian Provisional Patent Application 202111049484, filed Oct. 29, 2021, entitled SYSTEM TO DISPLAY GAMUT EXCURSION, the disclosure of which is incorporated by reference herein for all purposes. 
     FIELD OF THE DISCLOSURE 
     This disclosure relates to test and measurement devices, and, more particularly, to a system for measuring and reporting measurements of images and video. 
     BACKGROUND 
     The well-known CIE 1931 chromaticity diagram provides a straightforward way to visualize color in two dimensions, as illustrated by reference  100  in  FIG.  1   . The CIE 1931 chromaticity diagram was developed by the International Commission on Illumination in 1931 based on color observations of a set of ordinary observers. The two dimensions in the CIE chromaticity diagram  100  correspond to the x and y chromaticity values from the xyY color space, where x and y represent a color value and Y represents a luminance value. It is well known that the xyY color space is derived from the XYZ color space by normalizing the X, Y, and Z components against their sum. In the CIE chromaticity diagram  100 , the xy values from the xyY three-dimensional color space are projected into a two-dimensional plane along the Y axis. Some versions of the CIE 1931 chromaticity diagram include internal colors, while others, such as the CIE chromaticity diagram  100  of  FIG.  1   , illustrate just the outlines of the color gamut visible to ordinary observers. 
     Whereas the CIE chromaticity diagram  100  of  FIG.  1    illustrates the colors seen by the eyes of a standard observer, image-producing devices such as televisions, tablets, phones, computer monitors, and other types of displays generally do not display such a large color gamut. In fact, many color display and reproduction systems can represent only a small subset of the full chroma values shown in the CIE chromaticity diagram  100  of  FIG.  1   . 
       FIG.  1    also illustrates the bounds of three defined color gamuts, in this case ITU BT.  709  (a standard developed by International Telecommunication Union Radio communication Sector, reference  110 ), DCI-P3 (a Red Green Blue (RGB) color space developed by Digital Cinema Initiatives, reference  120 ) and ITU BT. 2020 (another standard developed by International Telecommunication Union Radio communication Sector, reference  130 ) superimposed on the entire 1931 chromaticity diagram  100 . A defined color gamut, like the gamuts  110 ,  120 ,  130  illustrated in  FIG.  1   , shows the outer edges of colors that are produced in the particular gamut. Colors inside the CIE chromaticity diagram but outside the particular gamuts are not colors supported by the particular gamut. Note that the gamut for ITU BT. 2020 ( 130 ) is larger than the other two gamuts ( 120 ,  110 ). This means that a device that conforms to ITU BT. 2020 gamut  130  is able to faithfully reproduce more colors than the other illustrated gamuts. Conversely, gamut ITU BT.  709  ( 110 ) is the smallest of the three illustrated gamuts, and cannot faithfully produce as many colors as the other two illustrated gamuts ( 120 ,  130 ). A television or other display may be qualified on its ability to properly display an entire defined color gamut. 
     A good use case for the CIE chromaticity diagram  100  is in color grading during cinema/television post-production. For example, a colorist might look at the distribution of colors for a scene in a CIE chromaticity diagram to determine if all the colors are within the expected gamut (e.g. ITU BT.709) or whether the colors are at the expected chromaticity locations. The ‘raw’ content used by the colorist typically contains a wide gamut of colors, for example up to the boundary of the ITU BT.2020 gamut  130 . The task of the colorist might be to grade the content in such a way that colors are remapped to within the DCI-P3 color gamut  120 , such as for cinematic display. 
     One of the most cited problems when using the CIE chromaticity diagram  100  and gamut boundaries is the issue of determining how far off colors are from a gamut boundary of interest. If the colors are close to a gamut color boundary, the colorist might decide to allow the colors to be clipped to a color at the edge of the gamut rather than risk a hue shift with color mapping. The small area between the gamut triangles, such as illustrated in  FIG.  1   , makes it difficult for a colorist to accurately assess whether and by how much the color of a particular pixel making up an image may be outside a specific gamut boundary. For example,  FIG.  2 A  is an example base image  200  (originally in color) and  FIG.  2 B  is a chart illustrating the color location of the original color pixels making up the original  FIG.  2 A  plotted on the CIE chromaticity diagram  100  and gamuts  110 ,  120 , and  130  illustrated in  FIG.  1   . Note that plotting a frame of video to the CIE chromaticity diagram  100  is effected by mapping only the color expressed by each pixel in the frame to the chromaticity diagram, and not the location of the pixels making up the frame. Each pixel making up the base image  200  has a particular color, and that color is expressed as a single location on the CIE chromaticity diagram  100 , or other chromaticity diagram. Mapping all of the colors of the pixels making a frame creates a collection of color dots, or pixels, on the chromaticity diagram. Because the CIE chromaticity diagram  100  includes all of the colors generally visible by humans, the colors of all of the pixels of any frame of video are able to be mapped to the CIE chromaticity diagram  100 . But, because certain gamuts, which are pre-defined collections of colors, do not cover the entire CIE chromaticity diagram  100 , as illustrated in  FIG.  2 B , it is possible that certain colors making an image may fall inside or outside of a particular gamut, even though all of the colors of the pixels making up a frame are represented somewhere on the CIE chromaticity diagram  100 . 
     Note how difficult it is to see whether any of the individual pixels is within or outside of a particular gamut, such as the wide distribution of colors outside the BT.709 gamut boundary  110 . As can be seen from the CIE chromaticity diagram  100  of  FIG.  2 B , it becomes difficult to estimate an amount of excursion outside the BT.709 gamut boundary  110 , especially for colors closer to blue or red. 
     Additionally, the non-linear nature of the overlapping gamut boundaries makes it difficult, and less intuitive, for a colorist to have a global view of the color excursions outside a particular gamut boundary. 
     Embodiments of this disclosure address these and other limitations in the state of the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a chart illustrating the CIE 1931 Standard Observer Chromaticity Diagram on which three color gamuts have been superimposed, which may be used by embodiments of the disclosure. 
         FIG.  2 A  is an image to be analyzed. 
         FIG.  2 B  is a color chart for the image of  FIG.  2 A   
         FIG.  3 A  is a chart illustrating an example color gamut excursion according to embodiments of the invention. 
         FIG.  3 B  is a graph illustrating a new method of communicating gamut excursion according to embodiments of the disclosure. 
         FIG.  4    is a flow diagram illustrating example operations to generate a gamut excursion graph according to embodiments of the disclosure. 
         FIG.  5    is a rendering of an example display screen of a measurement device including a gamut excursion graph according to embodiments of the disclosure. 
         FIG.  6    is a functional block diagram of a test and measurement instrument, such as a video analysis waveform tool, including a system to display gamut excursion according to embodiments of the disclosure. 
     
    
    
     DESCRIPTION 
       FIG.  3 A  is a diagram  300  illustrating an example color gamut excursion according to embodiments of the disclosure. Similar to the diagram of  FIG.  1   , the diagram  300  of  FIG.  3 A  illustrates the outline of the CIE 1931 chromaticity diagram  100 , as well as outlines for the ITU BT. 709 ( 110 ), DCI-P3 ( 120 ), and ITU BT. 2020 gamuts ( 130 ). Additionally, a white point  350  is illustrated near the center of the CIE 1931 chromaticity diagram  100 .  FIG.  3 B  is a graph  380  illustrating a new representation that visually communicates gamut excursion to a user according to embodiments of the disclosure, and is explained in detail below. In practice, the graph  380  may be produced on a display of a video analyzer, or other video measurement device. 
     For illustration purposes, assume that point P1 in  FIG.  3 A  represents the color of a pixel of interest in an image. Note how P1 is outside of the BT. 709 gamut  110 , but is within the BT. 2020 gamut  130  and DCI-P3 gamut  120 . In general, embodiments disclosed herein generate, other than in a CIE chromaticity diagram, a separate display that indicates whether a color of interested is outside a gamut of interest. Further, if the color is, in fact, outside the gamut of interest, embodiments of the invention use the graph  380  of  FIG.  3 B  to communicate which color the pixel is, and to what extent the color is outside the gamut. A user can then use the graph  380  of  FIG.  3 B  help visualize and determine the extent of the color violation of the gamut. 
     The graph  380  of  FIG.  3 B  includes a number of elements. First, a graph background  382  maps 0-359 degrees on its X-axis against a percent of excursion on its Y-axis. A color bar  384  (colored in the original) indicates a spectrum of colors from the CIE 1931 chromaticity diagram  100 . From left to right, the primary colors represented in the color bar  384  span orange, yellow, green, light blue, dark blue, magenta, and red. As seen in  FIG.  3 B , the color bar  384  is a continuous spectrum of colors. 
     A user may use the graph  380  of  FIG.  3 B  in a number of ways. For example, if the color of interest is merely a small amount outside the gamut of interest, a colorist may choose to allow the color to be clipped at the gamut, i.e, represented to the best degree possible, by the color at the edge of the particular gamut, even if it isn&#39;t the absolute actual color of the original pixel. Using embodiments of the invention, this decision may be made quickly and easily—and much more easily than searching for tiny pixels on a crowded gamut chart. 
     Referring back to  FIG.  3 A , embodiments of the disclosure construct a line segment between the white point  350  of the CIE chromaticity diagram  100 , through the pixel of interest P1, and ending at the edge of the outermost gamut in the analysis. In this example the outermost gamut is BT. 2020  130 , and Point A1 marks the end of the line segment at the edge of the gamut  130 . The line segment also includes a point B1, which is the point on the constructed line segment that is at the edge of the BT. 709 gamut  110 , which is the gamut of interest for this example, and the gamut illustrated in  FIG.  3 B . 
     A rotation/radial angle of the constructed line segment (i.e., the line segment from the white point  350  to A1) may also be measured from a relative starting point or starting line. In the example illustrated in  FIG.  3 A , the starting line (0 degrees) is a line from the white point  350  and A extending exactly horizontally along the CIE 1931 chromaticity diagram  100 . In other embodiments, the starting line may be an imaginary line  352  passing through the white point  350  and through the red primary of the BT. 709 gamut  110 , an imaginary line  354  passing through the white point  350  and through the red primary of the DCI-P3 gamut  120 , or an imaginary line  356  passing through the white point  350  and through the red primary of the BT. 2020 gamut  130 . Note that the starting lines  352 ,  354 , and  356  from the white point  350  through the primary red color of each gamut  110 ,  120 ,  130  are slightly different from the starting line extending horizontally through the white point  350 . This small offset is due to the red primary of each gamut  110 ,  120 ,  130  being in a slightly different location on the CIE 1931 chromaticity diagram  100 . Of course, the orientation of the radial reference line is arbitrary, and the relative rotation amount of the constructed line may be measured from any desired starting or reference line. For the illustrated example, the gamut of interest is BT. 709 gamut  110 . Providing a relative rotation distance to the user from a base line, in addition to providing a line length distance from a starting point to the pixel of interest, provides a mechanism to singularly identify a pixel of interest to the user. Also, although this embodiment uses a line length and rotation to locate the pixel outside the gamut of interest, other pixel location identifiers could be used, such as a grid system based on a Cartesian plane, or another location system. Note that, with reference to the CIE chromaticity diagram  100 , the term “pixel location”, or other similar language, refers to the location of the particular color within the chromaticity diagram  100 , and not the location of the pixel within the original frame of video that is mapped to the chromaticity diagram, as described above. 
     In the distance+rotation embodiment described herein, the length measurements, of the line segment from white point  350  to A1, may be performed in a number of ways. One such measurement method is to make a range beginning at the edge of the gamut of interest and ending at the largest gamut represented on the graph. In the illustrated example of  FIG.  3 A , Point B1 is a 0% reference (i.e., if a color point were located there it would be 0% outside of the gamut of interest), while Point A1 is a 100% reference. In other words, in this measuring method, the location of the point of interest, P1, is measured on a relative scale between 0% and 100%, which reflects the relative distance that the point P1 is between the gamut of interest and the outermost gamut in the CIE 1931 chromaticity diagram  100 . 
     After the line segment through the point P1 is constructed and the relative distance of P1 on that line segment is determined, and after the rotation angle of the line segment is determined, this information may be mapped onto the graph  380  ( FIG.  3 B ) and presented to the user. In this example, only a single pixel, located at P1 on the diagram illustrated in  FIG.  3 A , is being graphed on  FIG.  3 B , for ease of explanation as bar  386 . The representation of this pixel is illustrated by the bar  386  in  FIG.  3 B  is placed at approximately 120 degrees as measured from the reference line, and the bar graph shows that the pixel is approximately 20% outside of the gamut of interest. In this way, the graph  380  of  FIG.  3 B  conveys significant information about the extent to which the color of the pixel is outside the gamut, i.e., the excursion distance, as well as the color of the pixel itself. 
     Note that in this example,  FIG.  3 B  is illustrating a pixel color excursion outside of the BT. 709 gamut  110 . If instead the DCI-P3 gamut  120  or the BT. 2020 gamut  130  were being analyzed, then, the graph  380  would have no pixels outside the respective gamuts, and the graph  380  would remain blank for the particular frame being analyzed. In practice the graph  380  may be produced for any selected image frame, for any selected gamut, and the operator has a mechanism to manually or automatically step through the individual frames of interest in a video, searching for color violations of the gamut, which appear as bars of varying heights along the Y-axis and locations along the X-axis showing all of the gamut color violations for the particular frame being analyzed. Also, the user has a mechanism to select which gamut  110 ,  120 ,  130 , or others, for which the graph  380  is produced. 
     A user may set pre-defined thresholds to ease analysis. Illustrated in  FIG.  3 B  are two such thresholds, Threshold A and Threshold B, on the graph  380  to increase the ease at which the graph  380  conveys information of pixel color excursion outside a particular gamut. Threshold violations by a bar  386  could cause a variety of actions to occur. For instance, when a bar appears on the graph  380  that violates Threshold A, the bar  386  may change color, such as yellow. And, when a bar appears on the graph  380  that violates Threshold B, the bar  386  may change color to red. Threshold violations could instead or additionally be logged in a list, with a frame number, location angle, and percentage of gamut excursion for each gamut violation, which could be reviewed at a later time. The number of thresholds that may be generated is variable, and individual thresholds may be set for each color gamut being analyzed. In other words, the threshold levels need not be the same for all gamuts. 
       FIG.  4    is a flow diagram illustrating example operations of a flow  400  to generate a gamut excursion graph according to embodiments of the invention. The flow begins at an operation  402  when it receives a video frame for processing. The flow  400  receives some information, which may be received from the user or may be pre-set. For example, the flow  400  receives a selection of gamma  404 , a selection of gamut  408 , and a target gamut  416 . Then, the flow  400  proceeds through operations  406  to remove gamma,  410  to convert the color space to XYZ color space, and  412  to convert the color space from XYZ to xyY. The x and y coordinates from the operation  412  may be represented as (x,y), and referred to as the chromaticity coordinate of the particular pixel being analyzed. The operations  402 - 412  are conventional, and won&#39;t be further described. In some embodiments, the operations  402 - 412  are repeated for all of the pixels in a particular frame, or even in a particular portion of a video made from multiple frames, prior to being analyzed for gamut excursions in operations  414 - 428 . 
     The operation  414  compares the (x,y) chromaticity coordinate of the present pixel to determine whether it is inside or outside of the target gamut, such as BT. 709. If the (x,y) chromaticity coordinate of the present pixel is located within the target gamut, i.e., within the gamut triangle, then the pixel is ignored on the graph and operation  418  retrieves the next pixel to be processed. 
     If instead the (x,y) chromaticity coordinate of the present pixel is located outside of the target gamut, such as P1 relative to BT. 709 ( 110 ) in  FIG.  3 A , then the flow  400  continues to operations that build the excursion graph as above described with reference to  FIGS.  3 A and  3 B . 
     First, a line extension from the white point  350  through the (x,y) chromaticity coordinate of the present pixel is created in an operation  420 . In one embodiment the ends of the line are the white point  350  and the boundary of the outermost, i.e., widest, gamut that the gamut of interest is being measured against. In other embodiments the line length may be constructed or referenced differently, such as to other gamuts, or even to the edge of the CIE 1931 chromaticity diagram itself. With reference back to  FIG.  3 A , the line extends from the white point  350  to A1. 
     Next, the points of intersection of the constructed line and a) the edge of the gamut of interest; and b) the edge of the gamut of reference, are determined. With reference back to FIG.  3 A, these are points B1 and A1, which are the intersections of the constructed line with the BT. 709 gamut  110  and the BT. 2020 gamut  130 . 
     Then, in an operation  422 , a relative distance of the point P1 between points B1 and A1 is determined. In other words, how far does the point P1 extend between the points B1 and A1? In the example given with reference to  FIG.  3 A , the point P1 extends approximately 20% of the distance between B1 and A1. The relative distance may be expressed as a percentage as illustrated in an operation  424 . As described below, the relative distance of the excursion of P1 outside the gamut of interest may be calculated in other ways, using other line lengths in the percentage calculation. For example, other relative distance measurements may be used, such as references to a linear or non-linear scale. Thus, the particular reference used to measure the excursion may be implementation specific. 
     In parallel, a hue angle of the constructed line may be determined in an operation  426 . Recall from above that a reference line may be constructed from, for example, a line  352 ,  354 , or  356  passing from white point  350  through the red primary corner of the gamut of interest. Or, the reference line may be a horizontal line that extends from the white point  350  no matter which gamut is being used as the gamut of interest. Also, as mentioned above, the hue angle of the constructed line may be made from any desired line as the radial reference line. 
     Finally, after the hue angle is determined in operation  426 , the information generated in operations  420 - 426  is graphed for the pixel of interest in an operation  428  to create a representation of the pixel of interest on the graph, such as the graph  380  illustrated in  FIG.  3 B , and presented to the user. 
     Note that, in some embodiments, the operations  420 - 428  are repeated for every pixel in the selected image that is located outside the selected gamut of interest and mapped on a singular graph  380 . Therefore, unlike the example of  FIG.  3 B , the constructed graph for all of the gamut excursions in a video frame will likely contain many data points, likely on the order of hundreds or thousands. The graph may identify the frame number for the particular excursion. In another embodiment, individual graphs, such as  380 , may be constructed for each frame in a selected portion of a video. Then, the user could step through the individual graphs  380  to search for gamut violations. In yet other embodiments, only particular graphs  380  for frames that violate any pre-determined thresholds may be generated, including not only Threshold A and Threshold B, but also for any gamut color violation over 0%. 
     In general, the graph that is constructed according to that as described above helps a user quickly identify various colors that have an excursion outside of the target gamut boundary. 
       FIG.  5    is an image  500  of a display, also referred to as a display, of a test and measurement device that may be used to generate and show the above-described excursion graph to a user. The image being analyzed is a test image  510 , located in the upper-left corner of  FIG.  5   . A representation of colors  512  of the test image  510  may also be presented on the display. A CIE and gamut graph  520 , which is the present state of the art, is illustrated in the top center of the screenshot. The upper-right section of the display provides a user interface  530  through which the user can select the desired gamut, pixel persistence, luma qualifications, etc., to help define what the user will see on a display  540 , which may be an embodiment of the graph  380  of  FIG.  3 B . Along the bottom of the image is an example of the graph in the display  540  created as described above with reference to  FIG.  3 B . Spikes seen on the display  540  near 105 degrees show that there are green pixels in the test image that fall outside the selected BT. 709 gamut. There are other spikes around 150 degrees and a single spike near 180 degrees. These spikes on the graph of the display  540  alert the user to other color excursions beyond the selected gamut. Threshold A, Threshold B, and others may be set through the user interface  530  or by adding them to the display  540  and dragging them into a desired position. Further, a color bar  542  may be presented below the graph of the display  540  to give a quick reference to the user where the color of the image or video being processed goes beyond the selected gamut. Even further, the graph bars themselves may be presented in the actual colors that exceeded the gamut. Yet further, in some embodiments, pixels within the test image  510  may be modified during processing to produce false colors, or heat maps, with varying intensity related to those pixels of the image that include colors that fall outside of the selected gamut. Pixels of the test image  510  that have colors that fully fall within the selected gamut are not modified. Thus, when a user sees a test image  510  that has many false colors, the user can easily see where the color gamut excursions occur on the test image  510 . Although  FIG.  5    illustrates the various sections on a black background, the background of any of the sections and graphs may be another color, such as white. Also, not all of the elements of the image  500  need be present in all embodiments of the invention. 
     The gamut excursion graph concept described above can be applied to any source and target gamut boundaries, including gamuts that are not currently defined. Also, different representations of reference length (the denominator in the ratio of lengths) may be used for measurement of excursions in percentages. For instance, the graph illustrated in  FIG.  5    uses a ratio of the distance between points P1 and B1 to a distance between white point  350  and B1 ( FIG.  3 A ). So, in the case as illustrated in  FIG.  5   , it is possible that the graph height may exceed 100%. In other embodiments, excursion distances may use a non-linear scale. In yet other embodiments, excursion distances, in either a linear or non-linear scale, may be classified into definable excursion zones, so a Level 5 excursion may be a more severe gamut violation than a Level 2 violation. Like mentioned above, any reference may be chosen for either angle or distance without deviating from the scope of the invention, or other mechanisms to identify the pixel outside the chosen gamut may be used. 
     In some embodiments, the display  500  can be constructed using the  1976  CIE chromaticity diagram rather than the  1931  CIE chromaticity diagram  100  as illustrated herein. The  1976  CIE chromaticity diagram has an added advantage that distances between points on the chart are perceptually linear. That is, using the  1976  CIE chromaticity diagram, equal distances between points will show equal changes in chromaticity, unlike the  1931  CIE chromaticity diagram  100 . Of course, other chromaticity diagrams may also be used in other embodiments. 
       FIG.  6    is a functional block diagram of a test and measurement system  600  including a test and measurement instrument, such as a video analysis waveform tool, including a system to display gamut excursion according to embodiments of the disclosure. The test and measurement system  600  includes a source  610  for video to be analyzed as well as an instrument  620  for analyzing video, such as a video waveform monitor. The source  610  for the video may transmit the video for analysis through conventional means to the instrument  620 , such as through direct video connection or using an Internet Protocol (IP). 
     The instrument  620  includes a video input  622  for accepting the video from the source  610 , as well as a video processor  624  on which embodiments of the invention may operate. In practice, there may be multiple video inputs  622  within the instrument  620  for accepting multiple different streams of video from multiple sources  610 . 
     One or more processors  626  may be separate from the video processor  624 , or in some embodiments, the processing functions to operate the instrument  620  and perform the video analysis may be contained within a single processor. In other embodiments the processing functions to operate the instrument  620  and perform the video analysis may be spread across multiple processors, as is known in the art. The one or more processors  626  may be configured to execute instructions from memory  627  and may perform any methods and/or associated steps indicated by such instructions, such as receiving, analyzing, measuring, storing, and displaying results of such operations on a display  630 . The display  630  may be the same or similar to the display  500  described with reference to  FIG.  5   . The memory  627  may be implemented as processor cache, random access memory (RAM), read only memory (ROM), solid state memory, hard disk drive(s), or any other memory type. The memory  627  may also act as a medium for storing video data, computer program products, and other instructions, as is known in the art. The video processor  624  may include its own memory for similar functions, or may be coupled to and operate from the memory  627 . 
     User inputs  628  are coupled to the processor  116 . User inputs  628  may include a keyboard, mouse, touchscreen, and/or any other controls employable by a user to set up and control the instrument  620 . User inputs  628  may also include a graphical user interface on the display  630 , or may be entirely embodied by the display  630 . User inputs  628  may further include programmatic inputs from the user on the instrument  620 , or from a remote device. 
     While the components of test instrument  620  are depicted as being integrated within test and measurement instrument, it will be appreciated by a person of ordinary skill in the art that any of these components can be external to test instrument  620  and can be coupled to test instrument in any conventional manner (e.g., wired and/or wireless communication media and/or mechanisms). For example, in some embodiments, the display  630  may be remote from the test and measurement instrument  620 , or the instrument may be configured to send output to a remote device in addition to displaying it on the instrument  620 . In further embodiments, output from the measurement instrument  620  may be sent to or stored in remote devices, such as cloud devices, that are accessible from other machines coupled to the cloud devices. 
     EXAMPLES 
     Illustrative examples of the technologies disclosed herein are provided below. A configuration of the technologies may include any one or more, and any combination of, the examples described below. 
     Example 1 is a display for showing information from a video frame relative to a selected gamut, the selected gamut including a defined set of colors, the display including an indication of a pixel location for a pixel color in the video frame that exceeds those within the selected gamut, in which the indication of the pixel location includes a location reference that is referenced from a reference point. 
     Example 2 is a display for showing information from a video frame according to Example 1, in which the reference point is within the selected gamut. 
     Example 3 is a display for showing information from a video frame according to Example 1 in which the reference point is a white point. 
     Example 4 is a display for showing information from a video frame according to any of the preceding Examples, in which the indication is an element on a graph including an angular location reference and a distance reference to the pixel location from the reference point. 
     Example 5 is a display for showing information from a video frame according to Example 4, in which the distance reference is a distance from an outside edge of the selected gamut to the pixel location. 
     Example 6 is a display for showing information from a video frame according to Example 5, in which the distance is a relative distance of the pixel location between an outside edge of the selected gamut and a second reference point. 
     Example 7 is a display for showing information from a video frame according to Examples 5 or 6, in which the relative distance is a linear or non-linear representation. 
     Example 8 is a display for showing information from a video frame according to Example 6, in which the second reference point is an edge of a non-selected gamut. 
     Example 9 is a display for showing information from a video frame according to Example 6, in which the second reference point is an edge of a chromaticity diagram. 
     Example 10 is a display for showing information from a video frame according to Example 4, in which the representation is colored to match a color of the pixel color in the video frame that exceeds those colors within the selected gamut. 
     Example 11 is a display for showing information from a video frame according to Example 4, further comprising a color bar indicating an individual color of the selected gamut for each angular location reference. 
     Example 12 is a display for showing information from a video frame according to any of the preceding Examples, further comprising a visual representation of the video frame in which colors of individual pixels outside of the selected color gamut appear as falsely colored pixels. 
     Example 13 is a display for showing information from a video frame according to Example 12, in which colors of individual pixels within the selected color gamut retain their original color. 
     Example 14 is a video waveform monitor, including an input for receiving a video including one or more video frames, a video processor for analyzing the one or more frames of the video, and a display for showing information from the one or more video frames relative to a selected gamut including a defined set of colors, the display including an indication of a pixel location for a pixel color in the video frame that exceeds those within the selected gamut, in which the indication of the pixel location includes a location reference that is referenced from a reference point. 
     Example 15 is a video waveform monitor according to Example 14, in which the indication on the display is an element on a graph including an angular location reference and a distance reference to the pixel location from the reference point. 
     Example 16 is a method of illustrating an amount of gamut excursion of a pixel in a frame of video that has a color that is not within a defined set of colors for a selected gamut, the method including determining a color of a pixel in the frame, evaluating whether the color of the pixel is within the defined set of colors for the selected gamut, generating a location graph, and adding an indication on the location graph for only those pixels of the frame that have a color that is not within the defined set of colors for the selected gamut. 
     Example 17 is a method according to Example 16, in which the indication on the location graph includes a location reference for each pixel of the frame that has a color that is not within the defined set of colors for the selected gamut. 
     Example 18 is a method according to Example 16, in which the location reference is an element on the location graph that includes angular location references and distance references from a predefined reference point. 
     Example 19 is a method according to Example 17, in which the predefined reference point is a color point within the selected gamut. 
     Example 20 is a method according to Example 17, in which the distance references indicate a scaled distance between an edge of the gamut and a second reference point. 
     Example 21 is a method according to Example 19, in which the second reference point is an edge of a non-selected gamut. 
     Additionally, this written description makes reference to particular features. It is to be understood that the disclosure in this specification includes all possible combinations of those particular features. For example, where a particular feature is disclosed in the context of a particular aspect, that feature can also be used, to the extent possible, in the context of other aspects. 
     Also, when reference is made in this application to a method having two or more defined steps or operations, the defined steps or operations can be carried out in any order or simultaneously, unless the context excludes those possibilities. 
     All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. 
     Although specific aspects of the disclosure have been illustrated and described for purposes of illustration, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, the disclosure should not be limited except as by the appended claims.