ICtCp

Key takeaways

ICtCp belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect ICtCp to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of ICtCp from memory before moving on to harder problems.

Reference excerpt

ICTCP, ICtCp, or ITP is a color representation format specified in the Rec. ITU-R BT.2100 standard that is used as a part of the color image pipeline in video and digital photography systems for high dynamic range (HDR) and wide color gamut (WCG) imagery. It was developed by Dolby Laboratories from the IPT color space by Ebner and Fairchild. The format is derived from an associated RGB color space by a coordinate transformation that includes two matrix transformations and an intermediate nonlinear transfer function that is informally known as gamma pre-correction. The transformation produces three signals called I, CT, and CP. The ICTCP transformation can be used with RGB signals derived from either the perceptual quantizer (PQ) or hybrid log–gamma (HLG) nonlinearity functions, but is most commonly associated with the PQ function (which was also developed by Dolby). The I ("intensity") component is a luma component that represents the brightness of the video, and CT and CP are blue-yellow (named from tritanopia) and red-green (named from protanopia) chroma components. Ebner also used IPT as short for "Image Processing Transform". The ICTCP color representation scheme is conceptually related to the LMS color space, as the color transformation from RGB to ICTCP is defined by first converting RGB to LMS with a 3×3 matrix transformation, then applying the nonlinearity function, and then converting the nonlinear signals to ICTCP using another 3×3 matrix transformation. ICTCP was defined as a YCC digital format with support for 4:4:4, 4:2:2 and 4:2:0 chroma subsampling in CTA-861-H (that means that in limited range 10 bit mode 0, 1, 2, 3, 1020, 1021, 1022, 1023 values are reserved).

Derivation ICTCP is defined by Rec. 2100 as being derived from linear RGB as follows:

Calculate LMS from BT.2100 RGB: [ L M S ] = 1 4096 [ 1688 2146 262 683 2951 462 99 309 3688 ] [ R G B ] {\displaystyle {\begin{bmatrix}L\\M\\S\end{bmatrix}}={\frac {1}{4096}}{\begin{bmatrix}1688&2146&262\\683&2951&462\\99&309&3688\end{bmatrix}}{\begin{bmatrix}R\\G\\B\end{bmatrix}}}

Normalize the LMS by a non-linearity: If the PQ transfer function is used: [ L ′ M ′ S ′ ] = E O T F P Q − 1 ( [ L M S ] ) {\displaystyle {\begin{bmatrix}L'\\M'\\S'\end{bmatrix}}=EOTF_{PQ}^{-1}\left({\begin{bmatrix}L\\M\\S\end{bmatrix}}\right)}

If the HLG transfer function is used: [ L ′ M ′ S ′ ] = O E T F H L G ( [ L M S ] ) {\displaystyle {\begin{bmatrix}L'\\M'\\S'\end{bmatrix}}=OETF_{HLG}\left({\begin{bmatrix}L\\M\\S\end{bmatrix}}\right)}

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with ICtCp

Start with the simplest possible case. Write down what ICtCp claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to ICtCp before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about ICtCp ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of ICtCp

In research: ICtCp appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses ICtCp in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: ICtCp is common in secondary-school and first-year university syllabi. It links to neighbouring topics Color space, High dynamic range, Ultra-high-definition television, so understanding it makes those chapters shorter.
In everyday life: Look for ICtCp outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study ICtCp in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what ICtCp means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain ICtCp out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is ICtCp in simple terms?

ICTCP, ICtCp, or ITP is a color representation format specified in the Rec. ITU-R BT.2100 standard that is used as a part of the color image pipeline in video and digital photography systems for high dynamic range (HDR) and wide color gamut (WCG) imagery.

Why does ICtCp matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study ICtCp?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on ICtCp.