Eliminate Distortion in Wide Angle Images

Author: John Honovich, Published on Dec 09, 2008

Today's megapixel cameras have many advantages as long as you have the right lens for the job. When that includes covering large areas or reducing cost by installing fewer cameras, that lens is a wide angle lens. Until recently only fisheye lenses were available for an ultra wide field of view. Fisheye lenses create a curved and distorted image which no one seems to like. This significant distortion causes loss of resolution at the image edges.

In the past year a new rectilinear lens giving a different ultra wide view without the barrel distortion or loss of edge resolution of fisheye lenses has been developed. This report is an overview of wide angle lens technology and how we at Theia Technologies overcome fisheye distortion using Linear Optical Technology.

Kissing cousins

The real world is full of three dimensional people and objects. Creating a representation of this world on a two dimensional plane in a camera creates some optical effects, especially when viewed through a wide angle lens.

There are two approaches used when designing wide angle lenses:

  • Equal angular slices – each pixel receives an equal angle leading to barrel distortion in the image
  • Equal planar distances – each pixel images an equal distance in a plane, this is a rectilinear lens.

The two families of wide angle lenses create very different views of the world.

Rectilinear wide angle lens Barrel distortion wide angle lens

Most wide angle lenses including fisheye lenses have barrel distortion which comes from imaging equal angular slices of the world onto the sensor. A close kin, similar in application but different design, is to image equal planar distances in the real world onto the image sensor using a rectilinear lens. Until recently, rectilinear lenses were not available for wide angle applications. Theia Technologies has worked to develop this type of lens.

Rectilinear lenses keep straight lines in the real world straight on the image sensor. This creates an effect called 3D stretching or lean-over in which objects at the image edge seem to be stretched because they are being “flattened” onto a plane along the tangent angle from the lens. The wider the field of view (for rectilinear lenses), the more noticeable this effect. There is an additional benefit in increased resolution at the edges of the image because of 3D stretching.

In the picture below, both cars are the same width but since Car B is seen much more obliquely it appears to be stretched. The cars are the same width because they are in the same plane perpendicular to the camera and the lens images these equal planar measurements to equal distances on the sensor. The length is stretched due to flattening onto the sensor plane.

Image showing 3D stretching from an ultra wide angle rectilinear lens.

The wide angle cousin of the rectilinear lens has the well known barrel distortion seen in almost all wide angle lenses with fields of view greater than 80deg, including fisheye lenses. This distortion causes the image to look curved and resolution to be reduced as the object moves farther from the center of the image.

Distortion reduces the object width the further it is from the image center.
The same image taken with a rectilinear lens shows increased resolution towards the edge of the image.

The distortion effect can be eliminated with software (creating a rectilinear lens image) but at a cost in time or processing power. Objects at the edges of the image are compressed and detail information is lost. The information was already lost travelling through the lens and no amount of software (contrary to Hollywood’s view of video surveillance) will be able to recapture the information.

Natural habitat of wide angle lenses

Wide angle lenses are not a panacea but there are many applications that benefit from their use. For applications requiring large areas of coverage, an ultra wide angle lens on a megapixel camera is a cost saving opportunity that should be considered. Wide angle lenses can.

  • Reduce the number of cameras required to cover an area, reducing cost of installation, maintenance and monitoring,
  • Be used in place of a PTZ camera when post-incident PTZ is desired.
  • Effectively monitor large areas like parking lots, schools, and construction sites and
  • Be used in close-up applications such as ATMs, card-locked garage entries, and multi-door entryways where both high image detail and wide fields of view are required.

Conclusion

Megapixel cameras need high performance wide angle lenses that can display high resolution images of large areas. Fisheye lenses create barrel-distorted curved images requiring software image correction whereas rectilinear lenses correct distortion optically in the lens, an elegant and efficient solution.

Mark Peterson is the VP Advanced Technology at Theia Technologies.

2 reports cite this report:

Testing Wide Angle Megapixel Lenses - Theia SY125M on May 26, 2009
More pixels provide the opportunity for greater field of views and less cameras. However, stock lenses provided with cameras only offer moderately...
Upcoming Panoramic Megapixel Camera from Scallop on Jan 08, 2009
A startup is developing a low cost 180 degree panoramic camera that could have a significant impact in real world video surveillance deployments in...

Related Reports on Lenses

Camera Focusing Tutorial on Aug 09, 2018
A camera's focus is fundamental to quality imaging. Mistakes can cause important problems. In this guide, we explain focus issues and proper...
Avigilon H4 Multi-Sensor Adds 32MP, H.265, Analytics on Jun 13, 2018
Avigilon has announced the H4 Multisensor, the successor to their repositionable multi imager line, adding features like H.265, integrated IR,...
Top Features For Easy Camera Installation (Statistics) on Jun 05, 2018
Camera installation is the most fundamental and common task for video security technicians. Because of this, camera manufacturers market their...
Installing Box Cameras Indoors Tutorial on May 22, 2018
This tutorial starts our physical installation for video surveillance series, starting with Box Cameras, one of the oldest and most basic types....
Axis Launches First Stereographic Panoramic Camera on Apr 05, 2018
Fisheye panoramics have not had much innovation in the past few years, with their multi-imager cousins getting most of the advances, e.g.,...
Dahua 4K Micro 4/3 Camera Tested (IPC-HF8835F) on Apr 03, 2018
Dahua is going big. Their new 4K HF8835F Micro Four Thirds sensor is one of the largest now on the market. Dahua is claming: Starlight...
Camera Form Factor Guide on Mar 16, 2018
When selecting surveillance cameras, users may choose from a number of different form factors, each with its own unique strengths and weaknesses,...
Dahua 4K IR PTZ Tested on Aug 21, 2017
4K has made its way to IR PTZs. In this report, we examine the Dahua 6AE830VNI, a 4K PTZ with 30x optical zoom, 200m (~650') integrated IR, and...
IP Camera Specification / RFP Guide 2017 on Aug 14, 2017
RFPs are hard. Do them 'right' and it takes a lot of knowledge and time. Do them 'wrong' and you can be (a) unwittingly locked into a specific...
Technician Personal Protective Equipment (PPE) Guide on May 12, 2017
Technicians encounter multiple hazards when running wires and installing security devices. Wearing personal protective equipment, or PPE, helps...

Most Recent Industry Reports

The IP Camera Lock-In Trend: Meraki and Verkada on Jan 18, 2019
Open systems and interoperability have not only been big buzzwords over the past decade, but they have also become core features of video...
NYPD Refutes False SCMP Hikvision Story on Jan 18, 2019
The NYPD has refuted the SCMP Hikvision story, the Voice of America has reported. On January 11, 2018, the SCMP alleged that the NYPD was using...
Mobile Surveillance Trailers Guide on Jan 17, 2019
Putting cameras in a place for temporary surveillance where power and communications are not readily available can be complicated and expensive....
Exacq Favorability Results 2019 on Jan 17, 2019
Exacq favorability amongst integrators has declined sharply, in new IPVM statistics, compared to 2017 IPVM statistics for Exacq. Now, over 5 since...
Testing Bandwidth Vs. Low Light on Jan 16, 2019
Nighttime bandwidth spikes are a major concern in video surveillance. Many calculate bandwidth as a single 24/7 number, but bit rates vary...
Access Control Records Maintenance Guide on Jan 16, 2019
Weeding out old entries, turning off unused credentials, and updating who carries which credentials is as important as to maintaining security as...
UK Fines Security Firms For Illegal Direct Marketing on Jan 16, 2019
Two UK security firms have paid over $200,000 in fines for illegally making hundreds of thousands of calls to people registered on a government...
Access Control Cabling Tutorial on Jan 15, 2019
Access Control is only as reliable as its cables. While this aspect lacks the sexiness of other components, it remains a vital part of every...
Avigilon Favorability Results 2019 on Jan 15, 2019
Since IPVM's 2017 Avigilon favorability results, the company was acquired by Motorola and has shifted from being an aggressive startup to a more...
Gorilla Technology AI Provider, Raises $15 Million, Profiled on Jan 15, 2019
Gorilla Technology is a Taiwanese video analytics manufacturer that recently announced a $15 million investment from SBI Group, saying this...

The world's leading video surveillance information source, IPVM provides the best reporting, testing and training for 10,000+ members globally. Dedicated to independent and objective information, we uniquely refuse any and all advertisements, sponsorship and consulting from manufacturers.

About | FAQ | Contact