ColorBars

ColorBars

ColorBars ( [ int width, int height, string pixel_type ] )

Produces a video clip containing SMPTE color bars (Rec. ITU-R BT.801-1) scaled to any image size.

By default, a 640×480, RGB32, TV range, 29.97 fps, 1 hour long clip is produced.

int  width = 640

int  height = 480

Set size of the returned clip.

string  pixel_type = "RGB32"

Set color format of the returned clip.

May be any of the following: "YUY2", "YV12", "YV24" (v2.60), or (default) "RGB32".

ColorBarsHD

ColorBarsHD ( [ int width, int height, string pixel_type ] )

Added in v2.60, ColorBarsHD produces a video clip containing SMPTE color bars
(Rec. ITU-R BT.709 / arib std b28 v1.0) scaled to any image size.

By default, a 1288×720, YV24, TV range, 29.97 fps, 1 hour long clip is produced.

int  width = 1288

int  height = 720

Set size of the returned clip.

string  pixel_type = "YV24"

Set color format of the returned clip. Must be "YV24".

TV range

For both filters, in all color formats, luminance levels are TV range, where black=16
and white=235, within a total possible range of 0-255.

The table below show the TV-range values ColorBarsHD generates, and those same values as they should be after converting to full range.

Y_full = (Y_tv-16)  × 255/(235-16) // (for R, G, B, Y)

U_full = (U_tv-128) × 255/(240-16) + 128 // (for U, V)

Y_tv   = Y_full × (235-16)/255 + 16 // (for R, G, B, Y)

U_tv   = (U_full-128) × (240-16)/255 + 128 // (for U, V)

Color bar	TV range output								(expanded to full range)
	R	G	B		Y	U	V		R	G	B		Y	U	V
75% White	180	180	180		180	128	128		191	191	191		191	128	128
75% Yellow	180	180	16		168	44	136		191	191	0		177	32	137
75% Cyan	16	180	180		145	147	44		0	191	191		150	149	32
75% Green	16	180	16		134	63	52		0	191	0		137	54	41
75% Magenta	180	16	180		63	193	204		191	0	191		55	201	214
75% Red	180	16	16		51	109	212		191	0	0		41	106	223
75% Bue	16	16	180		28	212	120		0	0	191		14	223	118

These colors are at "75%" of maximum, per common broadcast practice. You may occasionally see "100%" color bars.^[1] They are rather useless, as you cannot detect gain or saturation that is too high on a signal that is already at maximum.

PLUGE

The lower part of the frame is called the PLUGE (also lowercase: "pluge") signal.
From left to right it consists of: -I, white, +Q, then a series of black and near-black bars: 0, -4, 0, +4 and 0 IRE relative to black.

Note 'IRE' is used here to mean 'percent luminance', on a scale from 0 (black) to 100 (white), ignoring the varying broadcast standards where black might be 0 IRE or 7.5 IRE depending on the country.

This section documents the ColorBars pluge only; ColorBarsHD's pluge is similar, but dispenses with -I and +Q

The table below show the TV-range values ColorBars generates, and those same values as they should be after converting to full range.

PLUGE Element	TV range output								(expanded to full range)
	R	G	B		Y	U	V		R	G	B		Y	U	V
-I	0	58	98		16	158	95		-19	49	95		0	162	90
100% White	235	235	235		235	128	128		255	255	255		255	128	128
+Q	59	15	126		16	174	149		50	-1	128		0	180	151
Black	16	16	16		16	128	128		0	0	0		0	128	128
-4 IRE	7	7	7		7	128	128		-10	-10	-10		-10	128	128
Black	16	16	16		16	128	128		0	0	0		0	128	128
+4 IRE	25	25	25		25	128	128		10	10	10		10	128	128
Black	16	16	16		16	128	128		0	0	0		0	128	128
(negative values will be clipped to 0)

The -I and +Q bars are vestigial artifacts of NTSC analog TV and are not really used any more.

The -4, 0 and +4 IRE bars can be used to set your monitor brightness – assuming your playback chain expands TV range (16-235) to full-range (0-255) as shown in the images above. The -4 IRE and 0 IRE bars should have the same apparent brightness (they should be as dark as the monitor can display), and the +4 should be a little brighter. If you can see the -4 bar, your monitor brightness is set too high; if you cannot see the +4 bar, your monitor brightness is set too low.^[2]

Note, the pluge signal goes out of 16-235 range in the -I and the -4 bars. These cannot be accurately converted to 0-255 range.

More information about the colorbars and the PLUGE can be found on the colorbars theory page.

Audio

For both filters, an audio tone is also generated. The tone is a 440Hz sine at 48KHz sample rate, 16 bit, stereo. The tone pulses in the right speaker, being turned on and off once every second. Level is 0 dBFS.

You can use Amplify to set a softer level (0dB can be a little deafening!)

ColorBarsHD
AmplifyDB(-20)

Broadcasting organizations usually specify an "alignment tone" accompanying colorbars at anywhere from -12 to -20 dBFS; if sending materials to another party, be sure to get their preferred alignment tone level. The exact level doesn't matter as long as all parties agree to it.

Miscellaneous

• Note, that for example

ColorBars(pixel_type="YUY2")

...is equivalent to

ColorBars(pixel_type="RGB32")
ConvertToYUY2(matrix="PC.601")  
# "PC.601" / "PC.709" don't scale the luma range

• When directly generating YUV format data, the color transitions are arranged to occur on a chroma-aligned boundary.

Changes

v2.60	Added pixel_type="YV24" to ColorBars. Initial release of ColorBarsHD.
v2.56	Added pixel_type="YUY2"/"YV12".