{"id":363,"date":"2025-10-12T20:03:29","date_gmt":"2025-10-13T03:03:29","guid":{"rendered":"https:\/\/videoq.com\/blog2\/?p=363"},"modified":"2025-10-12T20:16:38","modified_gmt":"2025-10-13T03:16:38","slug":"color-bars-reference-levels","status":"publish","type":"post","link":"https:\/\/videoq.com\/blog2\/2025\/10\/12\/color-bars-reference-levels\/","title":{"rendered":"Color Bars Reference Levels"},"content":{"rendered":"\n

Color Bars<\/strong> is the most used Test Pattern<\/strong>.<\/p>\n\n\n\n

At first it was defined in analog RGB<\/strong> signal format, then in analog composite NTSC\/PAL\/SECAM<\/strong> formats, then in analog component<\/strong> format (YPbPr<\/strong> aka YUV<\/strong>), and finally – in digital component<\/strong>\u00a0RGB and YUV<\/strong> formats.<\/p>\n\n\n\n

In accordance with ITU-R Recommendation BT.471 the nomenclature (type specification) of any color bars test pattern should consist of RGB levels as a percentage of Reference White in the following sequence:
\nWhite Bar \/ Black Bar \/ Max Colored Bars \/ Min Colored Bars.<\/p>\n\n\n\n

For 100\/0\/75\/0 “EBU Bars” the MathCAD RGB_Bars matrix in percents looks like this:<\/p>\n\n\n\n\n\n\n\n

\"\"
EBU Bars Levels, RGB, %<\/figcaption><\/figure>\n\n\n\n

WhiteBar = 100<\/strong>, Black = 0<\/strong>, ColBarsMax = 75<\/strong>, ColBarsMin = 0<\/strong>.<\/p>\n\n\n\n

For any color space the relative YUV values in percents can be obtained as a product of multiplication of RGB_Bars matrix by the transposed RGB to YUV conversion matrix matching the selected YUV color space:<\/p>\n\n\n\n

YUV_UHD = RGB_bars \u00d7 Transpose(RGB2YUVUHD)
\nYUV_HD = RGB_bars \u00d7 Transpose(RGB2YUVHD)
\nYUV_SD = RGB_bars \u00d7 Transpose(RGB2YUVSD)<\/p>\n\n\n\n

\"\"
EBU Bars Levels, YUV, %<\/figcaption><\/figure>\n\n\n\n

For practical applications we should convert the relative YUV values in percents to Narrow Range digital data levels.<\/p>\n\n\n\n

To cover several bit depth cases it is convenient to present digital levels in  “8 bit fractional” notation invented by BBC engineers; this notation is suitable for any numbers of bits.<\/p>\n\n\n\n

Here we use its “10 bit as 8 bit fractional” variant, so .25 means one LSB increment of 10 bit value, 0.5 means two 10 bit levels, and 0.75 means three 10 bit levels added to 8 bit (MSB) value \u00d74:<\/p>\n\n\n\n

\"\"
EBU Bars YUV Levels, 8 bit fractional<\/figcaption><\/figure>\n\n\n\n

The nomenclature of widely used SMPTE Bars is 75\/0\/75\/0.<\/p>\n\n\n\n

Thus, the only difference between SMPTE Bars and EBU Bars is the White Bar level. This 75% White Bar is often called “75% Gray” (strictly speaking, we should not call it “White”).<\/p>\n\n\n\n

For six other (colored)  bars the YUV values of SMPTE Bars are the same as shown in EBU Bars matrices above.<\/p>\n\n\n\n

The 75% Gray Level plays important role,  in 8 bit fractional notation its level is<\/p>\n\n\n\n

16 + 0.75 \u00d7 219 = 180.25<\/strong>, so the 8 bit rounded level = 180.<\/strong><\/p>\n\n\n\n

The exact value of 75% Gray  Level in 10 bit is<\/p>\n\n\n\n

16 \u00d7 4  + 0.75 (219 \u00d7 4) = <\/span>721<\/strong>, <\/span><\/p>\n\n\n\n

but for backward compatibility with 8 bit systems it is typically set to<\/span><\/p>\n\n\n\n

180 \u00d7 4 = <\/span>720.<\/strong><\/p>\n\n\n\n

The Vectorscope<\/strong> shows you color Hue<\/strong> and Saturation<\/strong>; in math terms it means the UV Vector Angle<\/strong> in degrees and Length<\/strong> in percents.<\/p>\n\n\n\n

See below  the MathCAD calculated vector representation of EBU Bars UV values and how UV vectors look on VideoQ VQV analyzer screen:<\/p>\n\n\n\n

\"\"
EBU Bars UV Vectors<\/figcaption><\/figure>\n\n\n\n

Strictly speaking,  traditional Vectorscope graticule  label “Saturation” has not much in common with the corresponding colorimetry parameter. Better name for this label could be “Chroma Intensity” or “Chroma Level”.<\/em><\/p>\n\n\n\n

Yellow rectangles on the VQV Vectorscope tool display show measured UV “Chroma Volume”. This is quite handy for at glance checks. Note that Chroma Volume numerical value differs from UV vector length  aka “Saturation”.<\/p>\n\n\n\n

Full VQV Vectorscope readout text covers several measured parameters (overall UV statistics and separate statistics of U and V components). In case of pristine test pattern all readout values should be the same:<\/p>\n\n\n\n