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As we know that RGB monitors requires separates signals for red, green, and blue components of the image but television monitors uses single composite signals. For this composite signal use YIQ color model.

But don't understand what's the significance of Y, I, Q components? Can anybody explain just the intuition rather than details.

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  • There are several sites where this might be on-topic, but please read their instructions carefully before posting. Your question may have been answered before, so be sure to do a search first. Video, Electrical Engineering, or Signal Processing. Finally, most sites do expect first-time users to have the basic knowledge of using Wikipedia and internet searchers as the first step.
    – rwong
    Nov 28, 2021 at 22:39
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    To give a quick summary, which can be found on the Wikipedia page for YIQ, (1) it is similar to YUV, where luminance is separated out and given a good chunk of bandwidth; (2) the two chrominance dimensions (U and V) are rotated into I and Q in order to further "compress" their bandwidth, exploiting human visual system's sensitivity of (or lack thereof) toward certain chrominance differences. In other words, it's all about squeezing analog visual information into limited bandwidth by allowing blurriness on chromatic detail that human eyes don't care.
    – rwong
    Nov 28, 2021 at 22:43
  • @rwong I have many color related questions from S. E., so is it off topic here?
    – Alok Maity
    Nov 28, 2021 at 22:46
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    I’m voting to close this question because it's about the definition of a color space, rather than anything to do with how software engineering concepts might relate to it. Nov 28, 2021 at 22:54
  • @Stack I just found that this question is potentially on-topic on Retro-Computing SE. See: NTSC tag on Retro-Computing
    – rwong
    Nov 29, 2021 at 15:49

2 Answers 2

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Important - a suitable forum for this question has been found: Retro-Computing Stack Exchange.

https://retrocomputing.stackexchange.com/questions/2205/ideal-resolution-for-color-computer-on-ntsc


Colors are of philosophical interest for a number of reasons. One of the most important reasons is that color raises serious metaphysical issues, concerning the nature both of physical reality and of the mind. Among these issues are questions concerning whether color is part of a mind-independent reality, and what account we can give of experiences of color. These issues have been, and continue to be, inextricably linked with important epistemological and semantic issues.

- The opening paragraph from Color, on the Stanford Encyclopedia of Philosophy


This question is somewhat inter-discipline because it may have involved:


However, it does not appear to involve software architecture and design, or anything related to the software development life cycle.


The inter-discipline nature of "colorspace" has been debated before on Meta Stack Exchange: Where to ask a question about colorspace theory?.

While it appears that many questions on colorspace (including this question and the earlier question that triggered the debate on Meta) were easy to answer by pointing to a Wikipedia article, non-trivial questions about colorspace may be unable to find a uniquely suitable forum to ask on the Stack Exchange network.


The question is fully answered in the third paragraph on the Wikipedia article on YIQ. Quoted:

The YIQ system is intended to take advantage of human color-response characteristics. The eye is more sensitive to changes in the orange-blue (I) range than in the purple-green range (Q)—therefore less bandwidth is required for Q than for I. Broadcast NTSC limits I to 1.3 MHz and Q to 0.4 MHz. I and Q are frequency interleaved into the 4 MHz Y signal, which keeps the bandwidth of the overall signal down to 4.2 MHz. In YUV systems, since U and V both contain information in the orange-blue range, both components must be given the same amount of bandwidth as I to achieve similar color fidelity.

Furthermore, the design of YIQ (i.e. the engineering decisions made to exploit then-available research into the human visual system) is described in the second paragraph:

In YUV, the U and V components can be thought of as X and Y coordinates within the color space. I and Q can be thought of as a second pair of axes on the same graph, rotated 33°; therefore IQ and UV represent different coordinate systems on the same plane.

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  • if color has high intensity means but has high frequency or high bandwidth?
    – Alok Maity
    Nov 29, 2021 at 10:31
  • @Stack The NTSC standard is quite old, and whenever it mentions bandwidth it literally refers to the width of the signal on the frequency domain (frequency axis). Refer to Fourier Transform to understand the theory on "frequency domain". Note that the signals Y, I, Q actually overlap significantly; they actually jam each other.
    – rwong
    Nov 29, 2021 at 15:31
  • Some more materials: (1) the specification as it was written (PDF)
    – rwong
    Nov 29, 2021 at 15:31
  • (2) A YouTube video that explains the NTSC signal (with a frequency plot for illustration) youtube.com/watch?v=3GJUM6pCpew&t=242s
    – rwong
    Nov 29, 2021 at 15:35
  • Amplitude modulation. In other words, if the color is more vibrant, the signal amplitude is literally higher.
    – rwong
    Nov 29, 2021 at 15:40
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YIQ color space corresponds to the encoding system used for NTSC color broadcast TV, which had as a requirement to use the absolute minimum bandwidth for the color information. Hence the wag's interpretation of the acronym, Never Twice Same Color.

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  • if color has high intensity means but has high frequency or high bandwidth?
    – Alok Maity
    Nov 29, 2021 at 10:30

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