Talk:YIQ

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These formulae are a bit much for the main article (and poorly presented), thus removed:

The approximate value of the matrix is:

\begin{bmatrix}Y\\I\\Q\end{bmatrix} = \begin{bmatrix}+0.299&+0.587&+0.114\\+0.595716&-0.274453&-0.321263\\+0.211456&-0.522591&+0.311135\end{bmatrix} \cdot \begin{bmatrix}R\\G\\B\end{bmatrix}

The exact value of the formula is:

Y  = + 0.299R + 0.587G + 0.114B
I  = + 0.877(R - Y) cos 33 - 0.492(B - Y) sin 33 = + [(0.877 cos 33)(1 - 0.299) - (0.492 sin 33)(-0.299)]R + [(0.877 cos 33)(-0.587) - (0.492 sin 33)(-0.587)]G + [(0.877 cos 33)(-0.114) - (0.492 sin 33)(1 - 0.114)]B
Q  = + 0.877(R - Y) sin 33 + 0.492(B - Y) cos 33 = + [(0.877 sin 33)(1 - 0.299) + (0.492 cos 33)(-0.299)]R + [(0.877 sin 33)(-0.587) + (0.492 cos 33)(-0.587)]G + [(0.877 sin 33)(-0.114) + (0.492 cos 33)(1 - 0.114)]B

The exact value of the matrix is:

\begin{bmatrix}+0.299&+0.587&+0.114\\((0.877 cos 33)(1 - 0.299) - (0.492 sin 33)(-0.299))&((0.877 cos 33)(-0.587) - (0.492 sin 33)(-0.587))&((0.877 cos 33)(-0.114) - (0.492 sin 33)(1 - 0.114))\\((0.877 sin 33)(1 - 0.299) + (0.492 cos 33)(-0.299))&((0.877 sin 33)(-0.587) + (0.492 cos 33)(-0.587))&((0.877 sin 33)(-0.114) + (0.492 cos 33)(1 - 0.114))\end{bmatrix}

The approximate value of the inverse matrix is:

\begin{bmatrix}1&1.176&0.764\\1&-0.411&-0.678\\1&-0.965&1.486\end{bmatrix}

The exact value of the inverse matrix is:

\begin{bmatrix}1&\frac{701}{500}\cos 33^\circ&\frac{701}{500}\sin 33^\circ\\1&\frac{101004\sin 33^\circ-209599\cos 33^\circ}{293500}&-\frac{101004\cos 33^\circ+209599\sin 33^\circ}{293500}\\1&-\frac{443}{250}\sin 33^\circ&\frac{443}{250}\cos 33^\circ\end{bmatrix}

--Dtcdthingy 07:30, 27 Nov 2004 (UTC)

Actually, the exact value of the inverse matrix is:

\begin{bmatrix}
+0.299 & +0.587 & +0.114
\\ ((0.877\cos 33)(1 - 0.299) - (0.492\sin 33)(-0.299)) & ((0.877\cos 33)(-0.587) - (0.492\sin 33)(-0.587)) & ((0.877\cos 33)(-0.114) - (0.492\sin 33)(1 - 0.114))
\\ ((0.877\sin 33)(1 - 0.299) + (0.492\cos 33)(-0.299)) & ((0.877\sin 33)(-0.587) + (0.492\cos 33)(-0.587)) & ((0.877\sin 33)(-0.114) + (0.492\cos 33)(1 - 0.114))
\end{bmatrix}^{-1}

=
\begin{bmatrix}
1 & \frac{1000}{877}\cdot\frac{\cos 33}{\cos 33^2+\sin 33^2} & \frac{1000}{877}\cdot\frac{\sin 33}{\cos 33^2+\sin 33^2} \\
1 & \frac{500}{21106759}\cdot\frac{16663\sin 33-24518\cos 33}{\cos 33^2+\sin 33^2} & \frac{-500}{21106759}\cdot\frac{16663\cos 33+24518\sin 33}{\cos 33^2+\sin 33^2} \\
1 & \frac{250}{123}\cdot\frac{\sin 33}{\cos 33^2+\sin 33^2} & \frac{250}{123}\cdot\frac{\cos 33}{\cos 33^2+\sin 33^2}
\end{bmatrix}
=
\begin{bmatrix}
1 & \frac{1000}{877}\cos 33 & \frac{1000}{877}\sin 33 \\
1 & \frac{8331500\sin 33-12259000\cos 33}{21106759} & -\frac{8331500\cos 33+12259000\sin 33}{21106759} \\
1 & -\frac{1000}{492}\sin 33 & \frac{1000}{492}\cos 33
\end{bmatrix}
=
\begin{bmatrix}
1 & \frac{1000}{877}\cos 33 & \frac{1000}{877}\sin 33 \\
1 & \frac{9500}{24067}\sin 33-\frac{299000}{514799}\cos 33 & -\frac{9500}{24067}\cos 33-\frac{299000}{514799}\sin 33 \\
1 & -\frac{250}{123}\sin 33 & \frac{250}{123}\cos 33
\end{bmatrix}

=
\begin{bmatrix}
1 & 0.9562948323208939905 & 0.6210251254447287141 \\
1 & -0.2721214740839773195 & -0.6473809535176157222 \\
1 & -1.106989908567128216 & 1.704614975498829329
\end{bmatrix}
--Zom-B 04:36, 9 Sep 2006 (UTC)
  • This uses a surreal amount of precision: 19 significant figures for a formula presented as approximate! I don't have the expertise to say how many figures are justified from these inputs, but I have cropped it down to 4 decimal places. I suspect 3 would be better. Notinasnaid 19:48, 21 March 2007 (UTC)

Crappy NTSC[edit]

Is the information reduction used with YIQ the reason why NTSC video pictures look sort of trashy and blurry compared to the PAL video system YUV? --Abdull 12:42, 23 Mar 2005 (UTC)

NTSC is only about 485 visible lines tall. If you round that down and use square pixels, it's 640x480. (familiar?) PAL is about 576 visible lines tall, and thus about 768x576 if you assume square pixels. This doesn't come free though; PAL is 50 fields (25 frames) per second while NTSC is 59.94 fields (29.97 frames) per second. PAL is jittery compared to NTSC. Even with the low framerate, PAL generally takes more bandwidth on the air. (it's a radio spectrum hog) AlbertCahalan 03:51, 23 May 2005 (UTC)
Because of the "485 visible lines" mentioned above, some square pixel calculations cited a figure of 648x486. –Wbwn 02:10, 6 September 2006 (UTC)
PAL allocates more bandwidth for color information (1.3MHz each for U and V) than NTSC (0.5MHz and 1.3MHz for I and Q). The PAL system also cancels out the color error that ends up right on the screen in NTSC. There's also much more luma bandwidth (6MHz vs 4.3 MHz). Combined with the lower frame rate, this allows much more detail to be present in each frame. --Dtcdthingy 20:03, 24 May 2005 (UTC)
I've read several sources that suggest that manufacturers switched to using 1.3MHz for both I and Q, as the lower bandwidth for Q was no longer required. This introduced a phase error of 33° for older televisions, but it could be simply fixed by adjusting the hue dial. It had the benefit of standardizing on the same low-pass filter for both I and Q, as well as negating the need for a delay circuit on the I line. The formula became "Q = B-Y cos33° + R-Y cos57°" and "I = -B-Y cos33° + R-Y cos57°" Dinjiin (talk) 09:06, 14 January 2013 (UTC)
Do the above ideas fit the topic of YIQ space? —The preceding unsigned comment was added by Scetpfe (talkcontribs) 03:21, 24 February 2007 (UTC).
This "comment" is a rude and ignorant attack on NTSC by someone who has little understanding of television systems.
First, NTSC and PAL are "Tweedledum & Tweedledee". There is no fundamental difference between them. In fact, the original NTSC proposal of 55 years ago, as given in an issue of Electronics magazine, was actually what became PAL (equal-bandwidth R & B primaries, polarity alternation).
Second, neither system discards much information. The color-difference signals represent saturation, and as most (not all!) objects (natural or man-made) have hues of constant saturation, this makes highly efficient use of the available the color bandwidth.
In the preceding response, the writer says "The PAL system also cancels out the color error that ends up right on the screen in NTSC." I assume he's referring to hue shifts caused by non-constant group delay. This was never a problem in the US, because American coax and microwave distribution systems had low differential phase error. Europe's equipment was not so good, which was one of the reasonas polarity alteration was used. Phase errors were of opposite polarity (and thus of complementary hue) on alternate lines, thus causing them to visually cancel. The "gotcha" is that the cancellation reduces saturation, introducing visible artifacts into the image. Yes, NTSC would have been subject to (arguably worse-looking) hue errors under the same conditions -- but the conditions were never the same.
There is another error in the preceding response, which states the PAL chroma signals are 1.3MHz. I've always understood them to be 1.0MHz -- narrower than the NTSC Q signal of 1.5MHz -- and this is consistent with the drawing in the Wikipedia article on PAL. If the claimed (non-existant) "information reduction" of the NTSC system makes its pictures "look sort of trashy and blurry", what can one then say about PAL, which has a narrower chroma bandwidth?
Yes, the European 625/25 standard does permit somewhat greater visual detail. Big deal. Neither system produces "trashy" or "blurry" pictures when properly used. The original poster should watch NTSC cable signals on a high-quality receiver and decide for himself whether NTSC has fundamental problems with image quality.
WilliamSommerwerck (talk) 18:26, 1 March 2008 (UTC)

Anyone?[edit]

Does anyone understand this subject enough to clean it up? It's been marked since april last year.

I changed it to {{expert}} to see if that'll attract anyone. 68.39.174.238 02:45, 14 April 2006 (UTC)

I have some minor expertise in this subject and I believe this article offers a good explaination of the subject.

Two technical statements in the article concerned me. Both were added by Mako098765.

The first was that the I and Q components refer to the "modulation schemes used" but they don't really they refer to the in-phase and quadrature-phase "components used in quadrature amplitude modulation".

The second was his explaination of the image. The origin he gave was not even on the diagram presented and he seemed to assume the I and Q components are polar co-ordinates when actually they are typically cartesian co-ordinates.

I have fixed both these problems, though this involved removing the image.

My only other concern was that the article was a little light in discussing how the YIQ colour space is used in image processing.

That said this article really does offer a good explaination of the topic, so I am removing the expert tag unless another expert offers a differing opinion.

Cedars 02:50, 18 May 2006 (UTC)

I got my info from the Buchsbaum TV servicing book that I mentioned. The color space diagram explanation may be somewhat suspect, but I am fairly confident about the modulation aspect, which refers to broadcast NTSC. From your comments about coordinates and image processing, you bring to mind YUV. - mako 06:09, 19 May 2006 (UTC)

Move page[edit]

I suggest that this article, as well as the YUV and YDbDr articles, be renamed so that the words "color space" or "color model" occur afterward. This way they adhere to the convention set by the other color space articles. -SharkD 02:13, 21 October 2006 (UTC)

I believe this is only necessary when there are conflicts with other article names. Valcumine (talk) 18:23, 28 June 2010 (UTC)

Image seems to be incorrect.[edit]

The first image of the article has incorrect coordinates. I and Q values never go above 0.6 or go below -0.6, atleast in the real world, which makes me question the authority of who made it. I'm not an expert, however. Valcumine (talk) 18:20, 28 June 2010 (UTC)

YIQ or YUV for NTSC?[edit]

Several other Wikipedia pages (e.g. the german YIQ page and http://en.wikipedia.org/wiki/Color_space) suggest that YIQ is actually no longer being used at all for NTSC. Can anyone confirm this? Beriechil (talk) 08:49, 13 November 2010 (UTC)y

  • Full power NTSC broadcasting in the US was discontinued by June 12, 2009. It's still used for low power stations, but that will be ending sometime in 2012. I'll update the article lead-in appropriately. Msaunier (talk) 14:21, 9 July 2011 (UTC)

Why 33 degrees?[edit]

Why did they choose 33 degrees exactly. Where did they derive that exact number from? — Preceding unsigned comment added by 157.178.2.1 (talk) 19:07, 8 November 2011 (UTC)

The first image on this page appears to be rotated by about 120 degrees (relative to YUV), not 33 degrees! For example, in YUV, Blue appears at the right (+X axis) while on this page Blue is near the top-left quadrant. I'm not saying the offset is exactly 120 degrees, but it is much greater than 33 degrees or the image(s) are wrong. Maybe 90 + 33 = 123 degrees ? Hydradix (talk) 09:54, 28 October 2012 (UTC)