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

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...
Varifocal Vs Fixed Lens Statistics 2017 on May 04, 2017
Varifocal camera lenses provide more flexibility at installation time, but come at a higher cost. Fixed lens cameras reduce hardware costs, but can...
Hikvision PanoVu Multi Imager Tested on Feb 08, 2017
Hikvision has entered the multi-imager market with their 180° PanoVu DS-2CD6986F-H, an 8MP, 4-imager model equipped with ~1/1.8" imagers and...
Avigilon Pro 4K Camera Tested on Jan 03, 2017
Avigilon is best known for their large sensor, high megapixel cameras. But with new offerings from Sony and soon Axis, the questions is how well...
Lens Iris Tutorial on Dec 19, 2016
Cameras, like humans, have irises. However, cameras have five types of iris options - fixed, manual, auto, P iris. In this tutorial, we explain the...
F-Stop Tutorial on Dec 16, 2016
To understand low light surveillance, appreciating the importance and role of the f-stop metric is critical. In this tutorial, we explain: Why...
Genetec Lower Cost Sharp V LPR Camera on Nov 23, 2016
Genetec has announced the latest offering in their AutoVu Sharp line, promising new features, simplified installation, and lower price. In this...
Testing EF Lenses On IP Camera on Nov 23, 2016
Glass. IP cameras are often characterized as using lower quality 'glass' and that those lenses reduce image quality. By contrast, Canon EF lenses...

Most Recent Industry Reports

Amazon Key In-Home Package Delivery Examined on Nov 21, 2017
Interesting idea or invitation for criminals to rob you? Amazon's recent announcement of Key, a service that will help manage visitors, welcoming...
Top Maglock Provider Warns Against Using Maglocks on Nov 21, 2017
Do not buy my company's product. It sounds strange indeed, but a senior Allegion consultant stated that maglocks should not be used in common...
CBR vs VBR vs MBR - Surveillance Streaming on Nov 21, 2017
How you stream video has a major impact on quality and bandwidth. And it is not simply CODEC choice (e.g., H.264 vs H.265). Regardless of the...
Dahua Hard-Coded Credentials Vulnerability on Nov 20, 2017
A newly discovered Dahua backdoor is described by the researcher discovering it as: not the result of an accidental logic error or poor...
Panasonic Unified Surveillance Strategy Analyzed on Nov 17, 2017
Panasonic is now a "Unified Surveillance" offering, as their ASIS 2017 booth proclaimed: Looking to make a comeback in the security industry,...
Amazon Cloud Cam Is Poor (Tested) on Nov 17, 2017
Retail behemoth Amazon has entered the surveillance market with the Amazon Cloud Cam, the eyes of its just-announced Amazon Key delivery...
Nest Secure Alarm System Tested on Nov 16, 2017
Google's expansion continues, this time into home security with their Nest subsidiary's move into alarm systems. They paid more than a...
Dahua Forbes 'Next Web Crisis' Vulnerability Dispute on Nov 16, 2017
The buffer overflow vulnerability in Dahua products is not in dispute, in fact we covered it when it was first published. What is in dispute is...
Isonas Cofounders Split, Launch Partner/Competitor on Nov 16, 2017
Breaking up is hard to do, especially when door access security is at stake. But that is exactly what has happened at Isonas. Senior employees...

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