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AUO Proprietary & Confidential

CCT Adjustment. 2008/10/6. Stockton Tsai. AUO Proprietary & Confidential. Agenda. Concept CCT Adjustment Algorithm Dark Level Fine-Tune P2:50, P1:15 Issue Feedback Fine-tune xy Previous xyY Previous Average P2 P1 Selection Panel Property Human Sense. B92. Color Temperature.

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AUO Proprietary & Confidential

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  1. CCT Adjustment 2008/10/6 Stockton Tsai AUO Proprietary & Confidential

  2. Agenda • Concept • CCT Adjustment Algorithm • Dark Level Fine-Tune • P2:50, P1:15 Issue • Feedback Fine-tune • xy Previous • xyY Previous • Average • P2 P1 Selection • Panel Property • Human Sense B92

  3. Color Temperature • Color Temperature • Blackbody locus • Corrected Color Temperature • Iso-temperature line • x=0.2788, y=0.2920 • (10000K, △uv=+0.0031) • x=0.2806, y=0.2883 • (10000K, △uv=0) 絕對色溫是唯一的, 相關色溫卻是有無限多種

  4. Color Temperature • Color Temperature of LCD (Gamma Off) • Blueish 盡量不要有起起伏伏的情形

  5. Gray Linearity 盡量不要有太大的轉折 DG Off DG On

  6. Gray Smooth • Brightness • Color • Adjacent • Global Brightness 色差 不連續 10 5 10 10 10 Adjacent 5 5 5 10 5 不連續

  7. Adjacent • Gray Smoothness 盡量不要有太大的peak DG Off也就是當Gamma 符合等間距且R=G=B時，相鄰顏色的色差是很小的 這些圖都只是輔助讓你更容易看出異色在哪邊, 某些Peak或是某些轉折會跟亮度有關 某些亮度下小的paek或轉折就可以看到異色, 但某些亮度下卻看不出來

  8. Human Vision Gamma 0-30(8 bit) Ex: TV W255:500 nit W0: 0.5nit gamma 2.4, 1nit W15 Monitor W255:350 nit W0: 0.3nit gamma 2.2, 1nit @ W15 實際調整最常出現異色也大概是在這區域附近 W10 -> W30 中介視覺

  9. CA210-Analyzer mode • CA210 Analyzer mode • Set Target White to CA-210 Memory • Wt -> Rt, Gt , Bt • Find the selected color RGB ratio to Target color • Wmeasure -> W_R=Rm/Rt, W_G=Gm/Gt, W_B=Bm/Bt ( RGB Intensity ) • RGB intensity are display in percentage (%) • W_R=W_G=W_B=100 => Target White • W_R=W_G=W_B=Const => 色彩跟Target White 一樣但亮度不同 Greenish Bluish RGB Intensity 目的就是希望所有灰階的W_R, W_G, W_B相等, 如何去決定其值就是本演算法的重點

  10. CCT Adjustment Algorithm AUO Proprietary & Confidential

  11. CCT Adjustment Algorithm • Step 0: Target White • Step 1: Measure Data • Step 2: Predict Luminance (L) • Step 3: Find the Relation between L and RGB • Step 4: Predict RGB • Step 5: Build Look Up Table

  12. Step 0: Setup Target White • Purpose • Input Target White to CA210 Memory • Method • Warm up panel (wait backlight stable) • Digit Gamma Off • 6 bit monitor : FRC Turn On • Target White • Use full-screen white pattern to adjust RGB value to desired color temperature (x, y) or (u', v'). • Record the data to a channel other than 0. This channel will be used for CCT and gamma calibration.

  13. Step 1: Measure Data • Measure data for specified gray levels • Luminance, CIE (x, y) and RGB intensities • Pattern for measurement • Full screen Gray 255 254 … 0. • For accuracy: Measure data at each gray level (4 minutes) • For efficiency: Measure data every 8 gray levels (40 seconds)

  14. Step 1: Measure Data 小數點後15位 某些暗灰階, CA-210 Analyzer mode無法分辨差異 這也是暗階我們直接用Digital Counts 計算而不用Intensity的原因之一

  15. Step 2: Predict Luminance • Assume L = a1R + a2G + a3B + a0 • Linear Regression • Find a0, a1, a2 & a3 • Max and Min Luminance • R = G = B = 100 => L(100) • L(0): measured • Gamma Luminance • W_L(N) = (L(100) - L(0)) x (N/255)gamma +L(0) • N: 0~255 W_RGB跟W_Y呈線性關係

  16. Step 3: Find Relation: L & RGB • Purpose • Calculate RGB intensity after adjusting luminance (L) to desired gamma • Calculate L • L = a1R + a2G + a3B + a0 • L=(a1 +a2 +a3)R +a0, R=G=B • Assume R = cL + d • c = 1/(a1 +a2 +a3) , d = -a0/(a1 + a2 + a3)

  17. Step 4: Predict RGB • Calculate gamma • W_L(N) = (L(100) - L(0)) x (N/255)gamma +L(0) • N: 0~255 • Calculate RGB intensity • Use R = cL + d (from Step 3), L = W_L(0), …, W_L(255) • G = B = R

  18. Step 5: Build Look Up Table • Use linear interpolation to obtain RGB gray level from RGB intensity • Convert 8-bit data to 10-bit data 1014=(253+(98.12946-97.48)/(98.66-97.48))*4

  19. Step 5: Build Look Up Table • Use linear interpolation to obtain RGB gray level from RGB intensity • Convert 8-bit data to 10-bit data 面板無法內插出此值 暗階不用Intensity的另一個原因 Gap

  20. Dark Adjustment • Gray < P1 • Digit Counts • P1=15, R = B = G =54 => RP(P1)=0.1572,GP(P1)=0.1912,BP(P1)= 0.2852 • From 0 to P1, Linear interpolation 查表內插 54以下線性內插

  21. Dark Adjustment • P1 < Gray < P2 • Intensity • B(P1+1)=B(P1)+(B(P2)-B(P1))*Gratio • Gratio=(G(P1+1)-G(P1))/(G(P2)-G(P1)) • G intensity trend • Use linear interpolation to obtain RGB gray level from RGB intensity • Smooth • RGB(P1)=(RGB(P1-1)+RGB(P1+1))/2

  22. Dark Adjustment for 6+3 FRC AUO Proprietary & Confidential

  23. Dark Adjustment for 6+3 FRC 6 gap 6 6 6 4 6 亮度Discontinuous G等差, RB 補償G修正值

  24. Dark Adjustment for 6+3 FRC Linear interpolation 6 4 選6以下作線性內插 經驗上灰階6以下的異色或不連續是不易發現 With G 等差4 以上方法在某些6+3 FRC Panel上暗灰階有時會出現異色

  25. Feedback Fine-tune • xy- previous • Compare with previous gray xy • xyY- previous • Compare with previous gray xyY • xyY- average • 5 Points moving average (i-2, i-1, i, i+1, i+2)

  26. Feedback Fine-tune Start Measure average xyY Measure Gray(i+1) xyY Measure Gray(i) xyY xy xyY average Calculate difference If △ > Th And Counter ≦ Loop Next Gray Adjustment

  27. Feedback Fine-tune Index (8bit) Value(10bit) • Method • Fill Gamma Value 0 1 2 3 ...255(10 bit) • So we can generate all color below 255(10bit) • For example: • Generate 163 151 116 (10 bit color) … 255 Use 8 bit to generate 10 bit color at low gray level

  28. Feedback Fine-tune Original Gamma • Method • Load Original Gamma • Input Initial Gray for Fix(Typical:50) • Generate Gray50(163 153 116) • Measure • Adjustment • Only can fix gray < 255(10 bit) … 以上方法雖已經有考慮到亮度因素去做調整, 但只要動到G, 就會產生亮度的不連續, 如果只動RB又無法調整出所要的色彩

  29. P2 P1 Selection • Adjacent Color Shift • Excellent:5 • Good:4 • Normal:3 • Poor:2 • Bad:1 • Global Color Shift • Excellent:5 • Good:4 • Normal:3 • Poor:2 • Bad:1 • Score (Adjacent + Global)

  30. P2 P1 Selection • P2=50, P1= 15 20 25 30 40 P1=15, 雖無Global異色, 但在W20 出現相鄰異色 偏藍 P1-P2急遽變化易出現Global 異色 偏黃 中介視覺 P1≧25, 出現顯著Global異色 1.因為P1越大, P1-P2間距離變短, 顏色變化越劇烈, 易出現異色 2.W30以上就屬明視視覺色彩敏度較高

  31. P2 P1 Selection • P2=50, P1=15 20 25 30 40 W20出現相鄰異色 △u’v’=0.0068@w19 無顯著相鄰異色 無顯著Global異色 無顯著相鄰異色 但有些微Global異色 無顯著相鄰異色 但有顯著Global異色 無顯著相鄰異色 但有顯著Global異色 P1以下接近Panel原始特性, 原本相鄰異色出現在W20, 所以P1只要設≧20, 就可解掉相鄰異色 但P1越大, P1-P2間距離變短, 顏色變化越劇烈, 易出現Global異色

  32. Gamma0(Reference) R=0,2,4…510 G=0,2,4…510 B=0,2,4…510 Gamma1(只調整R) R=2,4…510,512 G=0,2,4…510 B=0,2,4…510 Gamma2(只調整G) R=0,2,4…510 G=2,4…510,512 B=0,2,4…510 Gamma3(只調整B) R=0,2,4…510 G=0,2,4…510 B=2,4…510,512 Why P1= 20 ? Because the panel is 6+3 FRC, the minimum adjustment is 2 (10bit). Compare the difference of Gamma123 and Gamma0

  33. Why P1= 20 ? R跟B變化最劇烈都在48(12bit) 也就是8bit的灰階12, 0.0054@48 32~84 difference>0.004 0.0076@32 12~124 difference>0.004 0.0075@48 32~134 difference>0.004

  34. Why P1= 20 ? 最劇烈 如果設20就可以避掉較危險區域 Gray 5 ~44 的Gamma Table落於變化量較大的地方(即使調整最小調整量, △x或△y變化量>0.004),所以這些灰階的色彩Smoothness較差

  35. Summary • 重點一: 9bit Table 在暗灰階一定得等差4以避掉亮度的不連續 • 重點二: DG Off也就是當Gamma 符合等間距且R=G=B時, 相鄰顏色的色差是很小的, (目前解相鄰異色的方法) • P1=15，Adjacent color @W20 產生異色 • 灰階15 以上 >1 nit，椎狀細胞對色彩開始有感覺 • 灰階15的Gamma Table值 ≒50，為panel gamma調整色彩變化最大的區段 • P1到P2間的RGB Gamma Table值 不相等，此區域大多落於Panel 變化量最多的危險區域內，易出現不連續的異色。

  36. Summary • P1以下的點接近Panel原始特性, Panel原始特性(DG Off), 無顯著相鄰異色, △u’v’較小 • 假設在N階出現異色, P1只要設大於N就可以避掉此異色 • 此Panel在W0~W44的灰階調整色彩變化是最為劇烈 • 理論上P1>變化較劇烈的區段, 是比較安全的作法 • P2跟P1太接近且落在中介視覺較亮處,易出現Global異色 • P2跟P1太接近，也就是短灰階範圍內色溫急劇變化，視覺上會明顯看到一邊黃一邊藍的現象 • 急遽變化落在較亮處也較容易出現Global異色 • 此Panel P1=20, P2=50 • P1=20可以避掉W20的相鄰異色 • P1-P2為20-50, 但實際色溫急劇變化的部份約在35以下, 落在中介視覺, 也可以避掉Global異色 • 由於暗階採用Digital Count跟Intensity內差所以會出現一轉折點發生在交界處P1

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