Editing NTSC (section)

=== Colorimetry ===
[[File:CIE1931xy gamut comparison CC v06 NTSC 709 P3.png|thumb|1931 CIE chromaticity diagram, showing gamuts for NTSC, BT.709, and P3]]
{{See also|Color space}}

[[Colorimetry]] refers to the specific colorimetric characteristics of the system and its components, including the specific primary colors used, the camera, the display, etc. Over its history, NTSC color had two distinctly defined colorimetries, shown on the accompanying chromaticity diagram as NTSC 1953 and SMPTE C. Manufacturers introduced a number of variations for technical, economic, marketing, and other reasons.<ref>{{cite journal |title=Display Color Gamuts: NTSC to Rec.2020 |url=https://sid.onlinelibrary.wiley.com/doi/10.1002/j.2637-496X.2016.tb00920.x |access-date=July 15, 2024 |journal=Information Display |date=2016 |publisher=Frontline Technology|doi=10.1002/j.2637-496X.2016.tb00920.x |last1=Soneira |first1=Raymond M. |volume=32 |issue=4 |pages=26–31}}</ref>

{| class="wikitable"
|+ RGB chromaticity coordinates
! rowspan="2" | [[Color space]]
! colspan="2" | [[Standard illuminant#White points of standard illuminants|White point]]
! [[Correlated color temperature|CCT]]
! colspan="6" | [[Primary color]]s (CIE 1931 xy)
|-
! x
! y
! k
! R<sub>x</sub>
! R<sub>y</sub>
! G<sub>x</sub>
! G<sub>y</sub>
! B<sub>x</sub>
! B<sub>y</sub>
|-
| align="center" | NTSC (1953)
| style="background:#{{Color temperature|6774|hexval}}" | 0.31
| style="background:#{{Color temperature|6774|hexval}}" | 0.316
| style="background:#{{Color temperature|6774|hexval}}" | 6774 ([[Standard illuminant#Illuminants B and C|C]])
| style="background-color: color(rec2020 0.96 0.349 0.0);" | 0.67
| style="background-color: color(rec2020 0.96 0.349 0.0);" | 0.33
| style="background-color: color(rec2020 0.308 0.933 0.255);" | 0.21
| style="background-color: color(rec2020 0.308 0.933 0.255);" | 0.71
| style="background-color: color(rec2020 0.187 0.333 0.985);" | 0.14
| style="background-color: color(rec2020 0.187 0.333 0.985);" | 0.08
|-
| align="center" | SMPTE C (1987)
| style="background:#{{Color temperature|6500|hexval}}" | 0.3127
| style="background:#{{Color temperature|6500|hexval}}" | 0.329
| style="background:#{{Color temperature|6500|hexval}}" | 6500 ([[Illuminant D65|D65]])
| style="background-color: color(rec2020 0.806 0.351 0.176);" | 0.63
| style="background-color: color(rec2020 0.806 0.351 0.176);" | 0.34
| style="background-color: color(rec2020 0.645 0.953 0.352);" | 0.31
| style="background-color: color(rec2020 0.645 0.953 0.352);" | 0.595
| style="background-color: color(rec2020 0.299 0.224 0.957);" | 0.155
| style="background-color: color(rec2020 0.299 0.224 0.957);" | 0.07
|}
''<small>Note: displayed colors are approximate and require a [[Gamut|wide gamut]] display for faithful reproduction.</small>'' 

==== NTSC 1953 ====
The original 1953 color NTSC specification, still part of the United States [[Code of Federal Regulations]], defined the [[Colorimetry|colorimetric]] values of the system as shown in the above table.<ref>47 CFR § 73.682 (20) (iv)</ref>

Early color television receivers, such as the RCA [[CT-100]], were faithful to this specification (which was based on prevailing motion picture standards), having a larger gamut than most of today's monitors. Their low-efficiency phosphors (notably in the Red) were weak and long-persistent, leaving trails after moving objects. Starting in the late 1950s, picture tube phosphors would sacrifice saturation for increased brightness; this deviation from the standard at both the receiver and broadcaster was the source of considerable color variation.

==== SMPTE C ====
{{anchor|Color correction in studio monitors and home receivers}}

To ensure more uniform color reproduction, some manufacturers incorporated color correction circuits into sets, that converted the received signal—encoded for the colorimetric values listed above—adjusting for the actual phosphor characteristics used within the monitor. Since such color correction can not be performed accurately on the nonlinear [[Gamma correction|gamma corrected]] signals transmitted, the adjustment can only be approximated, introducing both hue and [[Luma (video)|luminance]] errors for highly saturated colors.

Similarly at the broadcaster stage, in 1968–69 the Conrac Corp., working with RCA, defined a set of controlled phosphors for use in broadcast color picture [[Display device|video monitors]].<ref name="DeMarsh, Leroy 1098">DeMarsh, Leroy (1993): TV Display Phosphors/Primaries&nbsp;— Some History. SMPTE Journal, December 1993: 1095–1098. {{doi|10.5594/J01650}}</ref> This specification survives today as the '''SMPTE C''' phosphor specification:<ref>{{cite web |title=SMPTE C Color Monitor Colorimetry RP 145-2004 |url=https://pub.smpte.org/latest/rp145/rp0145-2004_stable2010.pdf |access-date=July 15, 2024 |website=SMPTE}}</ref>

As with home receivers, it was further recommended<ref name="ITU470">International Telecommunication Union Recommendation ITU-R 470-6 (1970–1998): Conventional Television Systems, Annex 2.</ref> that studio monitors incorporate similar color correction circuits so that broadcasters would transmit pictures encoded for the original 1953 colorimetric values, in accordance with FCC standards.

In 1987, the [[Society of Motion Picture and Television Engineers]] (SMPTE) Committee on Television Technology, Working Group on Studio Monitor Colorimetry, adopted the SMPTE C (Conrac) phosphors for general use in Recommended Practice 145,<ref name="SMPTE_RP145">Society of Motion Picture and Television Engineers (1987–2004): Recommended Practice RP 145–2004. Color Monitor Colorimetry.</ref> prompting many manufacturers to modify their camera designs to directly encode for SMPTE C colorimetry without color correction,<ref name="SMPTE_EG27">Society of Motion Picture and Television Engineers (1994, 2004): Engineering Guideline EG 27-2004. Supplemental Information for SMPTE 170M and Background on the Development of NTSC Color Standards, pp. 9</ref> as approved in SMPTE standard 170M, "Composite Analog Video Signal&nbsp;– NTSC for Studio Applications" (1994). As a consequence, the [[ATSC standards|ATSC]] digital television standard states that for [[480i]] signals, SMPTE C colorimetry should be assumed unless colorimetric data is included in the transport stream.<ref>Advanced Television Systems Committee (2003): ATSC Direct-to-Home Satellite Broadcast Standard Doc. A/81, pp.18</ref>

Japanese NTSC never changed primaries and whitepoint to SMPTE C, continuing to use the 1953 NTSC primaries and whitepoint.<ref name="ITU470"/> Both the [[PAL]] and [[SECAM]] systems used the original 1953 NTSC colorimetry as well until 1970;<ref name="ITU470"/> unlike NTSC, however, the European Broadcasting Union (EBU) rejected color correction in receivers and studio monitors that year and instead explicitly called for all equipment to directly encode signals for the "EBU" colorimetric values.<ref name="EBU1975">European Broadcasting Union (1975) Tech. 3213-E.: E.B.U. Standard for Chromaticity Tolerances for Studio Monitors.</ref>

==== Color compatibility issues ====
In reference to the gamuts shown on the CIE chromaticity diagram (above), the variations between the different colorimetries can result in significant visual differences. To adjust for proper viewing requires [[Color management|gamut mapping]] via [[Lookup table#Lookup tables in image processing|LUT]]s or additional [[color grading]]. SMPTE Recommended Practice RP 167-1995 refers to such an automatic correction as an "NTSC corrective display matrix."<ref>{{cite web |title=SMPTE RP 167-1995 |url=https://pub.smpte.org/latest/rp167/rp0167-1995_stable2004.pdf |access-date=July 15, 2024 |website=SMPTE |page=5 (A.4) |quote=The NTSC corrective matrix in a display device is intended to correct any colorimetric errors introduced by the differ- ence between the camera primaries and the display tube phosphors.}}</ref> For instance, material prepared for 1953 NTSC may look desaturated when displayed on SMPTE C or ATSC/[[BT.709]] displays, and may also exhibit noticeable hue shifts. On the other hand, SMPTE C materials may appear slightly more saturated on BT.709/sRGB displays, or significantly more saturated on P3 displays, if the appropriate gamut mapping is not performed.