What is Metrology Part 17: Antialiasing

Antialiasing

We have done a good amount of learning within this series. With each new project and research oriented article, more knowledge is unraveled. We will be taking a look at antialiasing today as it was something that caught my attention in a previous article. It affects the accuracy of images as a whole, and we know the importance of precision in metrology

Antialiasing is a technique used to add greater realism to a digital image by smoothing jagged edges on curved lines and diagonals. This is a computer graphics technique that allows for sharper resolutions for a photo based on precise geometry. Some of the “imperfections” of an image may be distorted or destroyed due to this. I am certain that in order to do processing such as photogrammetry and image stitching, a computer would need exact geometries that can be added together to form a 3D image. This causes the 3D image to have less precision overall in terms of actual dimensions. 

Voltage Reading of an Anti-Alias Filter

An antialias filter refers to any filter that is used before a signal output, which in this case is our digital image. This filter is able to restrict the bandwidth of a signal. If we recall, we have talked about limiting signals before within this series in terms of filters (thresholding). We have defined this similarly as a low pass filter. A low pass filter does not allow for an image to pass through a specific energy level. This is what allows for filtering or cleaning of an image. 

The goal of antialiasing is to correct images. When certain defects are present, information cannot be correctly read by a device. Antialiasing is particularly useful when a picture is rasterized and has jagged appearance due to rasterization. Converting from an analog signal or image in the real world to a digital image causes distortion. This distortion needs to be filtered out, and antialiasing is one method that does such. 

There are more forms of antialiasing as well. The main forms include the following:

  • Spatial antialiasing
  • Temporal antialiasing 

Spatial antialiasing

In digital signal processing, spatial antialiasing is a technique for minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution. Why would we want to do this? When thinking in terms of the 3D world, spatial antialiasing is vital. Most of our images taken in the real world if done properly will be high resolution. In order to stitch together high resolution, one needs a large amount of storage for the data that would be stitched. In order to do this in a more effective way, it is better to convert the image data into lower resolution images and then stitch them. This requires less intensive data and storage. We can then convert the lower resolution image stitch later into higher resolution 3D models after spatial antialiasing methods are used. 

Temporal Antialiasing

Temporal Sample Anti-aliasing (TSAA) seeks to reduce or remove the effects of temporal aliasing. Temporal aliasing is caused by the sampling rate (i.e. number of frames per second) of a scene being too low compared to the transformation speed of objects inside of the scene; this causes objects to appear to jump or appear at a location instead of giving the impression of smoothly moving towards them. To avoid aliasing artifacts altogether, the sampling rate of a scene must be at least twice as high as the fastest moving object. The shutter behavior of the sampling system (typically a camera) strongly influences aliasing, as the overall shape of the exposure over time determines the band-limiting of the system before sampling, an important factor in aliasing. A temporal anti-aliasing filter can be applied to a camera to achieve better band-limiting. A common example of this can be seen when seeing a car wheel move backwards while we see it in video

There is still more to unpack knowledge wise. The rabbit hole continues to open up. There are different forms of antialiasing methods within the two sections provided today as well. I will be addressing some of these things within the next article.  Hopefully I will show these things off too with code.

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3Dflow Computer Vision Software

3Dflow

3Dflow

3Dflow is a private software company operating in the field of Computer Vision and Image Processing. It was established in 2011 as a spin-off of the University of Verona, and in  2012 it became a spin-off of the University of Udine. 3Dflow is a company that provides solutions in Photogrammetry, 3D modeling of reality, 3D processing, and 3D visual effects. Their customers range from small industries competitors to large scale entertainment companies. In this article we will be analyzing this company as well as showcasing their workshop for 3D imaging and photogrammetry, as well as their world cup competition.

3Dflow is a company that is based in Italy. It is a small organization with fewer than 15 employees. The main value proposition this organization gives is its ability to use computer vision and software in combination to create 3D image data. For the stitching of the point cloud data of multiple photos, the organization provides software that does this for the user. The software is called 3DF Zephyr. 3DF Zephyr comes in the following forms:

  • 3DF Zephyr Free
  • 3DF Zephyr Lite
  • 3DF Zephyr Pro
  • 3DF Zephyr Aerial

Image result for 3d flow photogrammetry

3DF Zephyr Free

The free version of 3DF Zephyr includes full 3D construction, a 50 photo limit, single NVIDIA GPU support, basic exporting capabilities, and basic editing tools, and full forum support. 3DF Zephyr Lite differences include Dual NVIDIA GPU Support, 1 year upgrades included, basic email, and full forum support. The 3DF Zephyr Pro version has full exporting capabilities, advanced editing tools, control points & measurements, laser scan support, 1 year upgrades included, full email, and forum support. 3D Zephyr Aerial has all the previous abilities and GIS, CAD, and Survey Tools. 

3Dflow still comes from an educational background in terms of its founding story. It explains how they have transitioned to a consulting company as well as an organization that is focused on research and development. It also explains why they offer a free version of their software as an educational version for students. They care about building software for the future of photogrammetry as well as 3D imaging. They have developed specific algorithms and frameworks that are proprietary to their organization. This includes:

  • 3DF Samantha
  • 3DF Statsia
  • 3DF Sasha
  • 3DF Masquerade

3DF Stasia is the proprietary algorithm to extract very accurate dense point clouds from a set of 2D images. In Computer Vision this process is best known as a multiview stereo. The first step is to extract the corresponding points in two images and the second step is the 3D reconstruction with algorithms like Discrete Linear Transform. The Discrete Linear Transform, or Discrete Fourier Transform used in a linear model, converts a finite sequence of equally-spaced samples of a function into a same-length sequence of equally-spaced samples of the discrete-time Fourier transform (DTFT), which is a complex-valued function of frequency. The function we are dealing with in this case is the stitching together or images into 3D object data. Using DLT, the reconstruction is done only where there are SCPs. By increasing the number of points, the results improve but it is time consuming. This method has low accuracy because of low reproducibility and time consumption. This method is dependent on the skill of the operator. This method is not suitable for bony structures with continuous shape. This method is generally used as an initial solution for other methods. Hence the other technology developed by 3DF is vital. 

Mathematics of Discrete Fourier Transform

3DF Sasha is their proprietary algorithm for mesh extraction: given a dense point cloud full of details, it is important to preserve as much detail as possible when extracting the surface. Sasha allows one to get sharp edges on a 3D model and that is why it is more suitable for applications such as architecture, industrial surveying, and urban monitoring. Without the precision of point cloud data, the resulting stitch of 2D images would come out to be noisy. 

To clean up residual noise from the data, 3Dflow employs their 3DF Masquerade tool. This tool has been developed as an external executable that is included in the 3DF Zephyr installation package. Masquerade can mask images so it can save time during masking operations. 3DF Masquerade is helpful when there is a lot of background noise or when the subject has been moved incoherently with the background: the most common scenario is a subject that is being acquired on a turntable.

Image result for noisy 3D data

Example of a Noisy 3D mesh

 

The first photogrammetry & 3D scanning training course in the English language by 3Dflow in Verona (Italy), next September 30th, October 1st and October 2nd! One will learn photogrammetry with 3DF Zephyr: this course will tackle everything from photography for photogrammetry (basic and advanced shooting techniques) to data processing with 3DF Zephyr, on both photogrammetry-only workflows and a external-data oriented workflows (e.g. laser scanners). Theory and practice on the software will be paired with an actual test-acquisition Verona, a world-famous history-rich cities in Italy and home of 3Dflow. 

I will be attending this workshop to learn and report on this next month, but I encourage others to look into the 3Dflow organization and see what they are doing. Also be sure to signup for their workshop here.

 

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What is Metrology Part 8: Complex Analysis, Optics, and Metrology

The field of metrology is interesting for me as it integrates a lot of what I enjoy in physics and technology. The field from the outside seems very bland, but when you delve into the background, it becomes a more colorful picture. The field is reliant on the physics behind optics and image processing. These are areas of extreme interest to me. Visualization and capturing visualization data is essential for the field. A lot of this data is difficult to interact with as well because the data must be interpreted as a function that can be manipulated for reconstruction purposes from point cloud data. The mathematics behind this is what can be referred to a complex analysis. Today I will give some basic insight into these advanced concepts of physics and how they open us to learning more about metrology and 3D scanning. 

Let’s first talk about the field of optics. Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.

Optical science is studied in many related disciplines including astronomy, various engineering fields, photography, and medicine. Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fibre optics, as well as metrology practices.


Yes Imaginary Numbers are useful

I personally have a strong fascination with the field of optics. Firstly, I wear glasses and my glasses help me “see” more. The field of optics quickly takes a dive into metaphysical thought processes on human perception as well as what we actually see. Optics is the center of how most of us “see” the world. When we are in the field of metrology we are relying on man-made technology to measure what we see as humans. The realization that we as humans are measuring reality and physical dimensions is a bit mind-boggling. We do not necessarily know what reality is, but we use metrology to measure for us what is within our “grasp”.

Here is where it starts to become a bit more interesting. What defines the system we are in as humans who are measuring within their current state of reality? There must be a larger system that allows for this to occur. This is where complex analysis comes into play. Complex analysis, traditionally known as the theory of functions of a complex variable, is the branch of mathematical analysis that investigates functions of complex numbers. It is useful in many branches of mathematics, including algebraic geometry, number theory, analytic combinatorics, applied mathematics; as well as in physics. As a differentiable function of a complex variable is equal to the sum of its Taylor series (that is, it is analytic), complex analysis is particularly concerned with analytic functions of a complex variable (that is, holomorphic functions).

Complex Analysis 3D Function

For those of you intimidated by math, I will explain the meaning behind the math. Complex analysis is the branch of mathematics that is trying to understand the imaginary or complex plane of the universe we are confined to. We are working within 3 degrees of freedom or 3-dimensionality within our universe. The system of the universe is not determined by what is seen in the 3-dimensional world. Our perception is not what easily moves the universe. The forces that work on our 3-dimensional universe are applied through the fourth dimension or the complex plane of the universe. For all those who want to learn more physics be sure to enjoy immense philosophical implications. So why is all of this relevant to metrology and optics? Think about this. The signals or data we receive from viewing images is distorted by the complex realm. If it was not, there would be extremely high resolution images taken on a consistent basis. That tiny bit of blur in a photo, for example, is a byproduct of the complex world interacting with the physical realm we are within. This is what typically creates a noisy signal typically in physics. In signal processing, noise is a general term for unwanted (and, in general, unknown) modifications that a signal may suffer during capture, storage, transmission, processing, or conversion. Noise reduction, the recovery of the original signal from the noise-corrupted one, is a very common goal in the design of signal processing systems, especially filters. The mathematical limits for noise removal are set by information theory, namely the Nyquist–Shannon sampling theorem.

The data we are collecting, or information, is prone to noise. We live in the 3rd dimensions and the complex plane consistently is interacting with our signals or data. Thus we use filters to help with noise cancellation. This is the basis of image processing and digital image reconstruction. The algorithms being created currently for photogrammetric filters are extremely vital for the future of 3D reconstruction. These filters will rely heavily on the field of complex analysis to build better filters. Then we will have very clean 3D reconstructions from our metrology practices. For all those who are intrigued, I will continue to explain different items within the 3D metrology field.

The post What is Metrology Part 8: Complex Analysis, Optics, and Metrology appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

3D Pod Episode 7 3D Scanning & Interview With Direct Dimensions CEO Michael Raphael

MIchael Raphael is one of the most experienced and knowledgeable 3D scanning people worldwide. For years he and his company Direct Dimensions have been asked to 3D scan important buildings, monuments, submarines, aircraft and much more. In our first interview Max Brogue and myself talk to Michael about his diverse projects. We mention the Kinect, 3D scanners in phones, scanning buildings, the work Michael’s team did on the Avengers movie and the state and future of 3D scanning. We talk about the problems and useful technologies for different applications. We really enjoyed this conversation and hope you will love it as well.

You can find all of our podcasts here. The podcast of bioprinting is here, 3D printing in medicine is here, 3D printing guns is here, teaching in 3D is here, the fourth industrial revolution is here, and the first is here. You can listen to them all on Spotify and Apple as well.

 

The Manacor Museum Uses 3D Printed Replicas to Encourage Visitors to Touch Its Exhibits

3D printed oil lamps from the Roman, Islamic and late antique periods.

The Manacor Museum in Mallorca, Spain was founded in 1908 as an archeological museum, but has since evolved into a true historical museum, showcasing objects from across the historical spectrum. Even the building itself is of historical interest, having been constructed in the 13th century. The objects themselves are displayed behind glass cases or in cordoned off areas, but as many of them were objects of use, they seem to cry out to be held. Unfortunately, such handling can cause significant preservation problems and so most museums have become churches of ‘look, but don’t touch.’

Now, however, 3D printing is helping museums to bridge that gap in the sensual experience and the Manacor is the latest to take advantage of the technology. They are starting out with a small exhibit of 12 exact replicas of objects in their collections that have been reproduced and are being offered to the waiting fingertips of the museum’s public. The objects selected for recreation were chosen by the museum staff and then scanned using advanced photogrammetry performed by Néstor F. Marqués.

All of the objects have been 3D printed at full size so that the museumgoer can really understand how the objects looked and felt to those who were interacting with them when they were created. In addition, great attention was paid to recreating the smallest details, being printed with a layer precision of between 200 and 100 microns, and some even as fine as 50 microns when smaller details were an integral part of the object’s presence. The objects were not quite ready to act as replicas of the original until they were finished and painted by hand, by experts Margalida Munar and Bernat Burgaya, so as to be nearly indistinguishable from the originals.

3D printed oil lamps from the Roman, Islamic and late antique periods.

The exhibit of the 3D printed replicas is set to be available to the public until July 15, but it’s more than likely that the replicas won’t just be assigned to some dusty storage bin. Instead, the museum recognizes the potential of these objects to reach out to a wide variety of audiences, including visitors with vision impairments, who might otherwise not be able to experience the displays that the museum has to offer.

This type of 3D printed replication is becoming an increasingly common practice in museums as it allows them to inexpensively create interactive exhibits that work to draw their visitors into the experience of the objects on display.

3D printing process of a Roman marble herma (bust) of the god Bacchus.

The use of 3D technology not only helps to produce the objects in their physical form; it has been repeatedly demonstrated to be the most effective way to preserve the information about their physical aspects without causing any damage to the original objects themselves. Ironically, it is this no-touch approach that allows museums to create more possibilities for hands-on interaction than ever before.

What do you think of this news? Let us know your thoughts; join the discussion of this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.

[Source/Images: Sketchfab]