Monitoring HD and SD Color Gamut in a Broadcast Environment

Transcription

1 Monitoring HD and SD Color Gamut in a Broadcast Environment Basics of RGB and composite color space, introducing an efficient way to monitor color gamut problems #1

2 The RGB Principle With 3 light sources emitting the primary colors RGB it is possible to create almost any color on a black background The pictures show the color bar colors derived from mixing RGB #2

3 Broadcast Signalflow PAL DVB SDI RGB RGB RGB #3

4 Broadcast Signalflow Image sensors work in RGB (HD and SD) CCDs, tubes Camera outputs often are SDI (YCbCr) SD: ITU-R 601 HD: SMPTE 274M & 296M In broadcast production, content management and playout the predominant signal format is SDI (YCbCr) Transmission uses PAL or DVB signals Final viewing is in RGB, regardless of display device CRTs: EBU phosphor LCDs, Plasmas, Projectors, PCs, #4

5 Broadcast Signalflow In high end production and postproduction signals are kept in RGB to maintain the highest possible quality Sony HDCAM-SR, Thomson D6 High end RGB and YCbCr formats (Dual Link) RGB and YCbCr 4:4:4, 10bit RGB and YCbCr 4:4:4, 12bit YCbCr 4:2:2, 12bit #5

6 Broadcast: RGB and Y Cb Cr Color Space RGB: 0mV to 700mV SD-SDI: ITU-R 601 Y = 0.587G B R Cb = (B-Y) Cr = (R-Y) HD-SDI: ITU-R 709 Y = G B R Cb = (B-Y) Cr = (R-Y) #6

7 The SDI Color Space Y Cr Cb #7

8 The SDI Color Space Y Cr Cb #8

9 The SDI Color Space Y Cr Cb #9

10 The SDI Color Space Y Cr Bl 64 Cb #10

11 The SDI Color Space W Y 940 Cr Bl 64 Cb #11

12 SD Color Bar in RGB W Y R Cr Bl Cb #12

13 SD Color Bar in RGB W Y R G Cr B Bl Cb #13

14 SD Color Bar in RGB Y W Yl M R Cy G Cr B Bl Cb #14

15 ITU-R 601 RGB Color Space (SD-SDI) Y W Yl M R Cy G Cr B Bl Cb #15

16 ITU-601 RGB Color Space (SD-SDI) Y Cr Cb #16

17 SD: YCbCr vs RGB Color Space The native SDI color space is Y Cb Cr Inside the native SDI color space the YCbCr values of the color bar colors define the corners of the RGB color space The RGB cube is smaller than the YCbCr cube There are values in the YCbCr cube which have no legal RGB equivalent #17

18 SD-SDI vs HD-SDI Because of the 2 different matrix equations the corners of the RGB cube acc. to ITU-R 709 are different from the RGB cube following ITU-R 601 The 709 RGB cube is smaller than the YCbCr cube Again there are colors in the YCbCr cube which have no legal equivalent in 709 RGB Applying the wrong matrix will produce errors! #18

19 ITU-601 RGB Color Space (SD-SDI) Y Cr Cb #19

20 ITU-R 709 RGB Color Space (HD-SDI) Y Cr Cb #20

21 SD Vectorscope #21

22 HD Vectorscope #22

23 SD and HD Color Bar Waveforms 100% Color Bar - SD #23 100% Color Bar - HD

24 Gamut Errors Y Cb Cr is the native signal format RGB gamut errors can occur when Signals are created Camera / light settings, grafics Signals are manipulated Processing, logos, grafics Gamut errors will only show when signals get converted to RGB Errors can also occur when Signals originate in SD and are upconverted to HD Signals originate in HD and are downconverted to SD #24

25 Gamut Errors What is the problem? Artifacts Wrong colors How to cure gamut problems? Legalizer Force correction by clipping chroma and/or luma signals Can result in color or saturation changes Color correction Manual correction of problem areas Maintains the artistic impression Careful content creation #25

26 Gamut Errors How to spot gamut problems? Which gamut limit is violated? Upper or lower? Luminance or peak? Which color in the image is causing the problem? In RGB: which color component is causing the problem? Where in the image is the gamut violation? Gamut display requirements Intuitive interpretation Full information #26

27 RGB Gamut Iris Display #27

28 RGB Gamut Iris Display #28

29 RGB Gamut Iris Display #29

30 RGB Gamut Iris Display #30

31 RGB Gamut Iris Display #31

32 RGB Gamut Iris Display #32

33 RGB Gamut Iris Display #33

34 RGB Gamut Iris Display #34

35 RGB Gamut Iris Display #35

36 RGB Gamut Iris Display #36

37 Live RGB Gamut Iris Display #37

38 RGB Gamut Iris Display with Error #38

39 RGB Gamut Iris #39

40 RGB Gamut Iris Display Indicates gamut errors in a very intuitive way Color of graticule changes Shows that the gamut problem is caused by a red-yellow area in the picture Shows that the blue component is causing the problem Shows that there are some blacker-than-black parts in the picture #40

41 Composite Color Space Y Cr Cb #41

42 HD, SD and Composite Color Space Y Cr Cb #42

43 Composite Color Space Limits are determined by the allowed peak color subcarrier amplitude Lies within YCbCr color space Different from RGB color space, does partially exceed the limits of RGB #43

44 Composite Gamut Iris #44

45 Composite Gamut Iris ALUM+1/2AFT #45

46 Composite Gamut Iris ALUM+1/2AFT ALUM-1/2AFT #46

47 Composite Gamut Iris #47

48 Live Composite Gamut Iris Display #48

49 Composite Gamut Iris with Luma Error #49

50 Composit Gamut Iris with Chroma Error #50

51 Composite Gamut Iris Display Seperates luma gamut errors from chroma gamut errors Indicates gamut errors in a very intuitive way Color of graticule changes Shows that a gamut problem is caused by a green-cyan area in the picture (subcarrier peak) Shows when there are luminance level violations in the picture #51

52 Monitoring Color Gamut Using the Gamut Iris Display and the more traditional waveform and vector display the following input-output combinations of color spaces can be tested for gamut problems: Out RGB Comp SD-SDI RGB Gamut Iris Comp Gamut Iris HD-SDI RGB Gamut Iris Comp Gamut Iris In #52 SD-SDI HD-SDI Color Bar, Wfm, Vector Color Bar, Wfm, Vector

53 Questions? TVM Series VTM Series #53