WebinarGamut

7/27/2019 WebinarGamut

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Presented by Mike Waidson


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Agenda

Understanding color and human vision

Color Correction

Gamut Monitoring

Understanding Diamond Display

Introduction to the New Spearhead Display

Composite Gamut Monitoring using Arrowhead Display

Content Quality Assurance

Color and Gamut Monitoring2


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Basic Anatomy of the human vision system

http://webvision.med.utah.edu/index.html

3 Color and Gamut Monitoring

Physical part/elements

Eye, Lens and Retina Rods

Sensitive to Blue-green light

Used for vision under dark-dim

conditions.

Cones 3 Types of Cones

Sensitive to either

long wavelengths of light (red light)medium wavelengths of light (green light)

short wavelengths of light (blue light)

Optic nerve
http://webvision.med.utah.edu/imageswv/3cone.jpeg


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Color Model developing color spaces

CIE 1931 XYZ color space with 2% observer is still foundation of most

color models

Trichromatic stimulus (color value)

Lightness decreases towards not shown third dimmension

Saturation inceases towards edges

Black

White



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Color Correction

Primary Color Correction Focuses on Overall color correction of image.

Secondary Color Correction Focuses to enhance specific areas or components of the image.

Are used to change colors after shooting

Mostly used to enhance the message of an image by highlighting areas,

changing the tonal range of a particular area etc.

Key areas: Skin tone, sky, grass. Making it look real


Secondary Color CorrectionPrimary Color Correction


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RGB and YPbPr Color space.

YPbPr color cube shows Parallel-Piped of RGB colors Certain YPbPr values when converted to RGB will fall outside the

allowed range and will be out of Gamut


RGB Color Cube YPbPr Color Cube


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Gamut monitoring - The traditional way RGB domain


Maximum

Gamut

Minimum

Gamut


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How the DiamondDisplay is constructed



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Gamut monitoring Diamonddisplay

Configuration Menu

Selectable Gamut Thresholds

Gamut

Limits



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Diamond Display - Live Signal Gamut Errors Blue



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Diamond Display - Live Signal Gamut Errors



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Diamond Display - Live Signal Gamut Errors



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Diamond Display Live Signal Corrected Gamut



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Diamond Display Camera Balancing

Black Center

White Outer

Apex

White Outer

Apex



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Diamond Display Camera Balancing Red Error

Deviation from

verticalindicates color

balance error

In this case a

Red Gain

Error

Deviation from

center

indicates color

balance error

Black Offset in

Red Channel



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New Spearhead Display


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Can we make a new display that has metrics ofSaturation, Value and Lightness?

RGB gamut space as XY plot of

max(rgb) and min(rgb)

100%

100% 0%

0%

100%white

max(rgb)=m

in(rgb)

monochrom

eaxis

max(rgb) < min(rgb) triangle

(impossible)

max(rgb) > min(rgb) triangle

valid RGB space

50%

50%

min(r,g,b)

max(r,g,b

)

Simple linear rotation to make monochrome

axis vertical.

max(rgb)+min(rgb)

2

max(rgb) - min(rgb)0%

color-bars

black

black

color-bars

white

100%

50%100%

50%

valid RGB space

inside triangular area

monochrome

axis

max(rgb)=100%

min(rgb)=0

%

rotate 45 deg

(lightness)

(non-normalized

saturation)

Premise:

1) For gamut limit testing we are interested in the max and min values of R, G, and B.

2) Artistic metrics like Value and Saturation are functions of both max and min of R, G, and B.



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New Spearhead Display(Color Lightness, Saturation and Value)

X(i) = max(i) - min(i)

Y(i) = [max(i) + min(i)]/2

50%

75%

25%

100%

75%

50%

25%

Valu

e

Saturation(HSV)

Lightness

black

white

mono

chromeaxis

50%

100%

25%

102% (limit)

0%

-0.5%

105%

Spearhead triangular RGB Gamut space:

max(i) = maximum of r(i), g(i) , b(i);

min(i) = minimum of r(i), g(i) , b(i);in mV.

The space is bounded by 3 lines:

1) the vertical line (monochrome) where

max(i) = min(i),

i.e. Y(i) = max(i) = min(i), X(i) = 0;

2) the line of all possible 100% Saturated

colors where min(i) = 0, max(i) = 0..700mV

i.e Y(i) = max(i)/2, X(i) = max(i),or graphically the y = x/2 line;

and

3) the line of all possible 100% Value colors

where max(i) = 700mV, min(i) = 0..700mV

i.e Y(i) = 700mV/2 + min(i)/2,

X(i) = 700mV - min(i),

or graphically the y = -x/2 + 700mV

Note:All valid rgb values (r(i), g(i), or b(i)within the range 0.. 700mV) are contained

within the Spearhead triangular gamut

space. All invalid (or illegal) rgb values

(min(i) < 0, or max(i) > 700mV) are outside

the Spearhead gamut space. Adjustable

gamut limit detector thresholds are indicated

as graticule markers (i.e. -0.5% and 105%).



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How to Make Gamut MeasurementUsing Spearhead.

Select one of the tiles

1,2,3 or 4

Select Gamut button

Push and Hold Gamut to

bring up the menu

Use arrow keys or general

knob to select Spearhead

display.



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Rainbow (variable Hue) Test Pattern

100% Value

100% Sat

text

monochrome

monochrome



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Rainbow Patternwith SMPTE Pb/Pr Hue rotation (RGB gamut error)



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Rainbow Patternwith Color Corrector Green Gamma Adjustment Error



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Spearhead for Content Quality Control(RGB gamut limits)

Fold Diamond Horizontally and Vertically to form Spearhead

The Spearhead display indicates Out-of-Gamut RGB components (triangle boundary) Spearhead also indicates how much the Signal is OVER Saturated or OVER Value (or

BOTH) so that we can see what has to change to correct the signal back into gamut.

This way a better trade-off of reducing Saturation or Value (or both) without affecting

the Hue can be accomplished with the least compromise in artistic quality.



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Using Spearhead with a Color Corrector

100%

black

white

100%

0%

Adjust Setup

Adjust Chroma

Adjust Gamma and

gray-scale tracking

Adjust RGB Gain

Push back to monochrome

line with RGB gamma controls

Adjust RGB Black Level



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Image with Gamut error in Blacks and RGB Gain



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Image after Color Correction using Spearhead Display



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Image Enhancement using Spearhead Display

BeforeAfter

Limited to 75% Value

Negative black level

100% Value

utilizing full

gamut space

No negative blacks



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Composite Gamut Monitoring


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Understanding the ArrowheadDisplay

Luma

Limits

Upper Luma+Chroma

Lower

Luma+Chroma



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Graticules available for both PAL & NTSC

PAL Graticule

Keep trace within graticule

NTSC Graticule

Keep trace within graticule



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Arrowhead Display Live Signal

Keep trace within graticule limits of Arrowhead

Adjust Luma and black level controls for vertical adjustment

Adjust Chroma controls for horizontal adjustment



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Arrowhead Display vs Pseudo Composite Live Signal

Keep trace within graticule limits

Saves having to view Waveform and Vector displays



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Content Quality Assurance


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Tape QA

Video Session and Error Log provide a simplify the QA process

After program has been edited QA of Incoming program

QA of Duplication

Video Session

Provides summary of video

Error Log Reports errors based on Alarm settings

Provides log related to timecode

Allows easy navigation to errors



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Video Session

Provides Summary of Video

signal during session

Simple indication of Gamut

Errors

Lower case letters indicate

values go below threshold

Capital letters indicate value

exceeds threshold

In this case

Lower r,g,b & l indicate valuesare below threshold for this

SMPTE bars test signal



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Error Log

Provides log of

errors Related to

timecode

Internal time

of day

Simplifies QAprocess

Log can be

printed

via network

interface

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Conclusion

Important to ensure Gamut compliance

Tektronix Diamond and Spearhead displays can aid in RGB gamutadjustments

Allows user to visualize adjustment made during color correction or

camera balancing

Tektronix Arrowhead display is suitable for Composite Gamutadjustments

The Error Log and session display of the instrument allow operators to

pin point errors within the material



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More Information

Local Sales and [email protected]
mailto:[email protected]:[email protected]


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Question Time


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