The Trouble with Watts

I recently read an article in a well-known consumer-facing technical hobby magazine, where the author used the phrase, “watts per day.”  This is an erroneous concept (the technically-trained author should have known better), which illustrates a matter that is often confusing to the average person.

“Watts per day” is not a meaningful unit of measurement.

The watt (W) is a unit of power, which is defined as the rate at which energy is transferred or used. One watt is equal to one joule per second (J/s).

The unit of energy is typically measured in joules (J), but it is also commonly measured in watt-hours (Wh) or kilowatt-hours (kWh). One watt-hour is equal to one watt of power used for one hour, and one kilowatt-hour is equal to one kilowatt (1000 watts) of power used for one hour.

In other words, the “watt” conveys the notion of the rate of energy consumption. When we pay for energy consumed, we pay for kilowatt-hours.

Therefore, if you see the phrase “watts per day,” it is likely that the author was trying to convey the notion of power used over a period of one day, and the correct usage would be to express it in terms of watt-hours (or kilowatt-hours) per day.

As an example: if a piece of equipment is rated at 100 watts, and the equipment is used for 8 hours every day, then we can say that the equipment consumes 800 watt-hours of energy (not power) per day.

Additional reading: why “RMS watts” makes no sense!


What is the Ecliptic? — Sky & Telescope, September 2022 — Errata

The inaugural Sky & Telescope article of Beginner’s Space – What is the Ecliptic? already has a serious error: the Earth is drawn incorrectly! Even in this artful depiction, it’s clear that the orientation of the continents should be rotated clockwise by 23.4°.

In the equatorial-azimuthal projection used there, the Geographic North Pole of the Earth (which of course projects to the North celestial pole) should emanate from above central Canada, not from above eastern Canada, as drawn in the article. Similarly, the Celestial equator (not the Ecliptic) should be drawn as the projection of the Earth’s equator (as correctly described in the article), which of course runs across the top of South America.

Let’s hope not too many new readers are confused!


Broadcasting Commission of Jamaica Names Aldo Cugnini as Digital TV Transition Advisor

June 3, 2022 – The Broadcasting Commission of Jamaica has announced that longtime broadcast television expert Aldo Cugnini of AGC Systems is being retained to provide advisory services in support of Jamaica’s transition from analog to digital broadcasting and the analog TV switch-off. Several years in the making, Jamaica’s Digital Switch Over (DSO) will transition the island nation’s over-the-air television broadcasting system to the ATSC 3.0 digital standard.

“Aldo is an excellent addition to the Jamaica DSO team. He will also help to advance our relations with ATSC, as Jamaica joins the NexGen TV community,” said Cordel Green, Executive Director of the Broadcasting Commission of Jamaica.

A long-time Advanced Television Systems Committee (ATSC) member and technical committee participant, Cugnini will serve as Technical Advisor to the Commission, which will include support for rolling out ATSC 3.0 Transmission, Application and Presentation services, as well as providing input into the deployment of digital-to-analog converters for Jamaican viewers.

“I’m very excited to be part of the Broadcasting Commission technical team and I am proud to be helping to bring the most modern television standard available today to the broadcasters and people of Jamaica,” Cugnini said.

“ATSC welcomes Jamaica to the growing number of countries deploying ATSC 3.0 technologies with Television Jamaica blazing the trail, launching NextGen TV services in January this year,” said Madeleine Noland, ATSC President. “With many more Jamaican broadcasters preparing for service launches, there is much work yet to be done. With the selection of AGC Systems and Aldo as a long-time ATSC member, Broadcasting Commission of Jamaica has brought years of expertise to the project.”

On January 31, Jamaica joined South Korea and the U.S. in the adoption and transmission of an ATSC 3.0 digital terrestrial television service. TV Jamaica (TVJ) is offering free broadcasting services to viewers, with a variety of channels including TVJ, TVJ Sports Network, Reggae Entertainment Television and Jamaica News Network, and the Public Broadcasting Corporation of Jamaica.

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Regarding the Invasion of Ukraine

AGC Systems strives to conduct business at the highest level of competence, fairness, and ethics.  We routinely evaluate our relationship with customers, clients, and sponsors, and consider whether any change is needed in those relationships.

We are horrified at the current situation in Ukraine, and condemn its invasion by Russian military forces. 

It has come to our attention that one of our sponsors is known to have headquarters in Russia. While we are led to understand that they have no connection with the Russian government or any person or entity under U.S. and European sanctions, we cannot ignore the fact that the net result of our endorsement of the company and its products would be financial input into the Russian economy.

In addition, the State of New Jersey has enacted laws limiting or prohibiting dealings with businesses associated with Belarus or Russia.

For these reasons, and as a show of support for both the government and people of Ukraine and the governments of the United States and the State of New Jersey, we are immediately suspending endorsement and promotion of that company and its products and services. If any of these factors should change in a positive fashion, we will reconsider our position.

I know that all of my colleagues here and around the world pray for peace and are against all types of violence whatsoever.

Aldo Cugnini
President, AGC Systems LLC

8 March 2022

Image Stacking — Sky & Telescope, April 2022 — Errata

The following errata correct the April 2022 Sky & Telescope Article, Image Stacking Demystified, by Richard S. Wright, Jr.

  1. The cumulative image noise is proportional to the square root of the number of frames being stacked.
  2. Mathematically, the shot noise from the imager and associated electronics can be considered to be added to the signal.
  3. The horizontal axis in both graphs on p.56 should be labeled “number of stacked frames,” and the vertical axis should be labeled “quantity.”


1.  The S&T author writes, “Shot noise is also quantifiable — it’s simply the square root of the signal value.” This is incorrect, as are the numerical examples that follow the statement.1 The noise and signal components are separate entities, and one cannot say that one of them is a function (square root) of the other.  (Actually, some systems do have an interaction between the two, but those are usually 2nd-order, minor effects, and are not relevant in the image stacking situation.)  The noise value is completely determined by the physics of the imaging device and the transistors in the related electronics, and is independent of the signal – it’s even there when there is no signal (e.g., a dark frame).  The incorrect statement would imply that a dark frame has zero noise, which is not true: in addition to fixed pattern noise (which we can reduce by subtracting a dark frame when doing advanced image processing), the dark frame will have its own random noise, too.

What is really happening is the following.  When we stack multiple images, we are literally adding the images together, pixel-by-pixel.  That means that the signal components get added together, and so do the noise components.  When the images are properly aligned (registered), the signal components at each pixel from one frame to the next add together as correlated data, since they are part of the same image. This combination is literally a simple addition, so image stacking increases the signal component in proportion to the number of frames being stacked.

However, the noise component at each pixel from frame to frame is uncorrelated, because it is a random process.  The noise components add together as orthogonal vectors, which means that the noise value increases by the square root of the number of frames being added together.  (The stacked images are then re-scaled, so that the resulting image doesn’t get progressively brighter everywhere – but this, of course, scales the noise by the same amount.)  The signal-to-noise ratio improvement is therefore proportional to the square-root of the number of frames that are stacked.

2.  The S&T author writes, “It’s important to bear in mind that this noise is not something that gets added so much as something that’s missing.” This is incorrect.  The mathematical modelling and analysis of signals with noise accounts for each of these elements as an added component; there is nothing “missing” from the original signal, which still exists in the image capture.  In practice, this can be readily seen by using a spectrum analyzer, which will show that the signal and noise are separate components.  The shot noise from the imager and associated electronics should be considered to be added to the signal.

3.  The graphs on p.56 are labeled incorrectly. The horizontal axis in both graphs should be labeled “number of stacked frames,” and the vertical axis should be labeled “quantity,” as it represents either signal or noise in the left-hand graph, and signal-to-noise ratio in the right-hand graph.



There is a different quantity, known as photon noise, which is characterized as the square root of the photon signal, but this is not the dominant factor in our calculation of signal-to-noise ratio, because we are considering the net effect over a set of stacked frames.


Wikipedia: Shot Noise – note the discussion regarding “square root of the expected number of events.”

Wikipedia: Gaussian Noise – “values at any pair of times are identically distributed and statistically independent (and hence uncorrelated).”

Philippe Cattin, Image Restoration: Introduction to Signal and Image Processing.

Robert Fisher, et al, Image Synthesis — Noise Generation.




AGC Systems Key Participant in ITU-R Rapporteur Group and ATSC Planning Teams

The International Telecommunications Union (ITU) has published two new documents that support the planning and testing of ATSC 3.0 systems.  The documents are:

  • ITU-R Recommendation BT.2033-2 : Planning criteria, including protection ratios, for second generation of digital terrestrial television broadcasting systems in the VHF/UHF bands.
  • ITU-R Report BT.2495 : Methods for laboratory and field measurements for the assessment of ATSC 3.0 reception quality.

This brings the total number of new ATSC-related documents to five, which includes the Handbook on Digital Terrestrial Television Broadcasting networks and systems implementation, which was updated last year.

Several ATSC-3.0-related documents are also in the ITU-R deliberation process, which are expected to result in additional publications. AGC Systems has been involved in this process for several years, and leads several initiatives to develop these documents.

The International Telecommunication Union is the United Nations specialized agency for information and communication technologies (ICTs). Founded in 1865 to facilitate international connectivity in communications networks, ITU allocates global radio spectrum and satellite orbits, develops technical standards that ensure networks and technologies seamlessly interconnect, and strives to improve access to ICTs to underserved communities worldwide.

The Advanced Television Systems Committee, Inc. is an international, non-profit organization developing voluntary standards for digital television.  ATSC member organizations represent the broadcast, broadcast equipment, motion picture, consumer electronics, computer, cable, satellite, and semiconductor industries.  The ATSC mission is to create and foster implementation of voluntary Standards and Recommended Practices to advance terrestrial digital television broadcasting, and to facilitate interoperability with other media.

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WNET Group will be First NEXTGenTV Broadcaster in New York City

The WNET Group has announced plans to launch NEXTGEN TV service in New York City and surrounding areas – the #1 television market in the country encompassing approximately 7.45 million TV households.

AGC Systems is one of the key organizations supporting The WNET Group with extensive engineering testing and operational planning based on the ATSC 3.0 suite of NextGenTV technologies.

Neal Shapiro, President & CEO of The WNET Group, expects that this transition “will modernize the New York City broadcast market infrastructure to deliver high-quality broadcasts with the latest technology available.”

For more information, see the WNET Press Release.

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The Fórum Sistema Brasileiro TV Digital Terrestre (SBTVD Forum) has recommended to the Brazilian government the selection of several technologies proposed by ATSC for Brazil’s next-generation terrestrial digital television standard.  AGC Systems has been actively involved in the proposal and testing process, on behalf of several clients, resulting in adoption of the SL-HDR1 High Dynamic Range system and MPEG-H Audio coding.

ATSC President Madeleine Noland congratulated the ATSC IT-4 Brazil Implementation Team, of which AGC Systems’ Aldo Cugnini is a member. “IT-4 members have been diligently supporting ATSC technologies throughout the process and will continue their efforts in the upcoming phases of the SBTVD evaluation process.”

The SBTVD development of “TV 3.0” specifications and additional testing will continue over the course of the next two years.

For more information, see the ATSC Press Release.

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Cugnini to Present Talk on New Audio/Video Technologies

AGC Systems’ President Aldo Cugnini will deliver an online talk, entitled “New Audio/Video/Wireless Technologies For Home Entertainment.”  Scheduled for Thursday, November 18, 2021, 6:30PM EST, and hosted by the IEEE Consultants’ Network of Northern New Jersey, the talk will explain how new technologies like UHDTV, HDR, and HEVC enable audio and video devices to efficiently deliver the latest entertainment to consumers.

The talk is free, and can be accessed by registering here.

This presentation is partly sponsored by Elecard.  Click here for more information on their video and stream analysis tools.