Limiter

The standard known as Rec.601 or CCIR-601 (Studio Encoding Parameters of Digital Television...) defines standard quantization levels: for luminance, black is 16 and peak white is 235. For chrominance, the range is 16 to 240, with the center (grey) at 128. "The signal may occasionally excurse beyond" this range according to Rec.601.^{BT.601-7 (Annex 1, Table 3)}

Luminance or chrominance values outside this range are known to cause problems with some TV sets, so Limiter was created to clip them (or clamp them - both terms are used) to the ranges [min_luma, max_luma] and [min_chroma, max_chroma], which you may specify, but by default are the Rec.601 values listed above.

Syntax and Parameters

Limiter(clip clip [, int min_luma, int max_luma, int min_chroma, int max_chroma, string show ] )

clip  clip = (required)

Source clip. YUV only.

int  min_luma = 16

Y (luma) lower clamping limit.

int  max_luma = 235

Y (luma) upper clamping limit.

int  min_chroma = 16

U & V (chroma) lower clamping limit.

int  max_chroma = 240

U & V (chroma) upper clamping limit.

string  show = (empty)

Colorizes the pixels outside the specified [min_X, max_X] range.

If set, show must take one of the following values:

show	Effect
"luma"	colorizes out of bound luma
"luma_grey"	colorizes out of bound luma, and makes the remaining pixels grey
"chroma"	colorizes out of bound chroma
"chroma_grey"	colorizes out of bound chroma, and makes the remaining pixels grey

The colorizing is done as follows:

• YUY2: j,k=1,2 (chroma shared between two horizontal pixels p1 and p2: Y1UY2V)
• YV24: j,k=1 (no chroma shared)
• YV12: j,k=11,12,21,22 (chroma shared between 2x2 pixels Y11UY12V: Y21UY22V)

See Examples below.

Pixel Condition	Colorization
	show="luma"	show="luma_grey"
Yj < min_luma	red (pj)	red (pj)
Yj > max_luma	green (pj)	green (pj)
Yj < min_luma and Yk > max_luma	yellow (pj and pk)	puke (pj), olive (pk)
	show="chroma"	show="chroma_grey"
U < min_chroma	yellow	yellow
U > max_chroma	yellow	blue
V < min_chroma	yellow	cyan
V > max_chroma	yellow	red
U < min_chroma and V < min_chroma	yellow	green
U > max_chroma and V < min_chroma	yellow	teal
U < min_chroma and V > max_chroma	yellow	orange
U > max_chroma and V > max_chroma	yellow	magenta

Examples

# 1. Original image FFmpegSource2("sintel.mp4") Trim(4685, 4685) ColorYUV(analyze=true)

# 2. Exaggerated luma and chroma range [...] Levels(16, 1.0, 255-16, 0, 255, coring=false) Tweak(sat=2.0, coring=false) ColorYUV(analyze=true)

# 3. Limiter("luma") [...] Limiter(16, 235, 16, 240, "luma") ColorYUV(analyze=true)

# 4. Limiter("luma_grey") [...] Limiter(16, 235, 16, 240, "luma_grey") ColorYUV(analyze=true)

# 5. Limiter("chroma") [...] Limiter(16, 235, 16, 240, "chroma") ColorYUV(analyze=true)

# 6. Limiter("chroma_grey") [...] Limiter(16, 235, 16, 240, "chroma_grey") ColorYUV(analyze=true)

Changes

v2.60	Added support for YV24.
v2.56	Added show to show out of bound luma/chroma.