What a fisheye camera is, how 360 degree coverage works, where dewarping runs, the pixel density penalty at the edge, and fisheye vs multi sensor vs PTZ.
A fisheye camera sees an entire room from one ceiling mount, with no blind spot beneath it.
Detail falls towards the edge of the circle. Plan on detection and observation, not identification.
Use IEC 62676-4 pixel densities to check what the camera can actually achieve at each distance.
Pair fisheye with narrow field cameras at entrances, where identification actually happens.
Record the original circle. Camera side only dewarping throws away footage of the rest of the room.
Test analytics at the edge, not in the middle of the image where demonstrations are filmed.
A PTZ camera records only where it points. A fisheye camera records everything, at lower detail.
A fisheye camera is a fixed security camera fitted with an ultra wide angle lens, usually covering 180 degrees, that records a circular image of the whole area around it. Mounted on a ceiling and pointing down, one fisheye camera sees 360 degrees horizontally, from the floor directly beneath it out towards the walls. Software then "dewarps" the circular image into flat, normal looking views an operator can read.
People use the terms loosely, so here is how they relate.
Fisheye camera: one lens and one sensor, producing a circular or near circular image.
360 degree camera: a description of coverage, not of construction. Most 360 degree security cameras are fisheye cameras; some are multi sensor.
Panoramic camera: usually 180 degrees horizontally, built either from one wide lens or from two to four sensors stitched together. Typically wall mounted.
Multi sensor camera: several separate lenses and sensors in one housing, each aimed in a different direction. Covers 180 or 360 degrees at much higher detail per direction.
An ordinary lens follows a rectilinear projection: straight lines in the world stay straight in the picture. That breaks down beyond roughly 100 to 120 degrees, because keeping lines straight stretches the edges more and more, and the image would need to be infinitely large to reach 180 degrees.
A fisheye lens drops the requirement. It maps angles onto the sensor so that a whole hemisphere fits into a circle. Straight lines curve and objects near the edge of the circle are compressed.
The exact mapping is called the projection model. The common ones are equidistant (distance from the centre of the image is proportional to the angle from the lens axis), equisolid angle, stereographic and orthographic. They differ in how much they compress the edges. The model matters in practice because dewarping software has to invert it: if the software assumes the wrong model for your lens, straight lines in the dewarped view come out slightly bent.
Ceiling mount is the default and the reason fisheye exists. Pointing straight down, the camera covers 360 degrees with no blind spot underneath, which a wall mounted camera always has. This suits retail floors, lobbies, open plan offices, warehouses with open aisles, classrooms and waiting rooms.
Wall mount gives a 180 degree panorama of the space in front of it. It is useful along corridors and at entrances, although a purpose built panoramic or multi sensor camera usually does the job with better detail.
Mounting height matters more than most specifications. A typical ceiling of 2.7 to 4 metres works well. Much higher, and people at the edge of the circle end up very small in the frame. Much lower, and the camera is easy to tamper with and sees the tops of heads rather than faces.
This is the part the product pages skip.
A fisheye camera with a 12 megapixel sensor does not give you 12 megapixels of usable detail wherever you look. The lens projects a circle onto a rectangular sensor, so the corners of the sensor are unused. That circle then covers a whole hemisphere, where a normal camera's full sensor covers perhaps 90 degrees. On a ceiling mount, people directly beneath the camera are closest and appear largest, while people towards the walls are both further away and compressed by the projection, so detail on the target falls steeply towards the edge.
The useful way to reason about this is pixel density on the target, measured in pixels per metre. IEC 62676-4, the international standard for video surveillance system application, sets widely used reference densities for different operational tasks.
At 25 pixels per metre an operator can detect that a person is present. At 62.5 pixels per metre they can observe what the person is doing and see characteristic details. At 125 pixels per metre they can recognise whether it is someone they know. At 250 pixels per metre they can identify the person beyond reasonable doubt.
A high resolution fisheye camera on a normal ceiling comfortably detects and observes across the room. It reaches recognition density close to the centre of the image. It generally does not reach identification density anywhere except directly beneath the camera, and not at all towards the walls.
That is the most important sentence in this guide. A fisheye camera tells you what happened in the room. It rarely tells you, on its own, who did it. The standard design is to pair a fisheye for awareness with a narrow field camera at each entrance, where every person passes close enough to be identified.
Dewarping takes the circular fisheye image and projects it back into flat views that look like normal camera footage. There are three common output types.
Virtual PTZ. One flat view the operator can pan, tilt and zoom within the circle, like a digital PTZ camera with no moving parts.
Panorama. The circle unrolled into a wide strip, often shown as two 180 degree halves.
Quad view. Four virtual cameras at 90 degree offsets, shown in a grid.
Where the dewarping runs affects bandwidth, storage and what you can do with recordings later.
On the camera. The camera sends already flat streams. This is simple for the VMS, but many implementations throw away the original circle, so a recording holds only the views that someone chose in advance. You cannot re examine a part of the room nobody was looking at.
On the server. The VMS receives the full circle, records it, and dewarps it centrally. The full image is preserved, but every dewarped view costs server compute.
On the client. The browser or viewing application dewarps the circle locally, usually on the graphics processor. The full original image is recorded, every viewer can look wherever they like independently, and the server pays nothing for it. The limit is that the dewarped view exists only on the screen: nothing downstream sees it.
Our recommendation for most sites is to record the original circle and dewarp on the client or server, so that the whole room is always available for investigation. Dewarping only on the camera is the one choice that is hard to reverse.
Most object detection models are trained mainly on normal, rectilinear imagery. On a fisheye image, a person near the edge of the circle is rotated, compressed and seen from an unusual angle, which is not what the model learned from. Detection generally holds up well near the centre and degrades towards the edge.
There are two approaches. You can run analytics on dewarped views, which gives the model familiar geometry but loses the parts of the room outside those views. Or you can use models trained on overhead fisheye imagery, which are less common. Counting and occupancy near the centre of the circle tend to work well. Identification grade analytics such as face recognition generally do not belong on a fisheye camera, for the resolution reasons above.
Whichever platform you use, test detection at the edge of the circle on your own footage before relying on it. Performance at the edge varies with the lens, mounting height and model, and a demonstration filmed at the centre of the image tells you little about the edge.
Coverage. Fisheye and multi sensor cameras both cover 180 to 360 degrees all the time. A PTZ camera covers one direction at a time.
Detail at distance. A fisheye camera is lowest, and detail falls towards the edge of the circle. A multi sensor camera is high in every direction. A PTZ camera is very high, but only where it is pointed.
Recording the whole scene. Fisheye and multi sensor cameras record everything in view. A PTZ camera records only where it was pointing.
Moving parts and cost. Fisheye and multi sensor cameras have no moving parts; a PTZ camera has motors, which wear. Fisheye is usually the cheapest of the three, multi sensor the most expensive.
Best use. Fisheye suits open rooms and overhead awareness. Multi sensor suits large outdoor areas and perimeters. PTZ suits tracking and zooming on live events.
The PTZ row carries a warning that applies to any mixed deployment. A PTZ camera records only where it is pointing. If it was zoomed on one incident while another happened behind it, there is no footage of the second. A fisheye camera cannot miss the second incident, although it may not resolve it in much detail. Many well designed sites use both: a fisheye camera for continuous whole scene recording, and a PTZ camera for detailed live follow up.
Prices vary widely by resolution, build and brand. As a rough guide, consumer and small business fisheye cameras cost from under a hundred US dollars, while enterprise fisheye cameras with 9 to 12 megapixel sensors, good low light performance and vandal resistant housings typically cost several hundred to over a thousand dollars each.
The camera's price is only part of the cost. One fisheye camera often replaces two to four fixed cameras in an open room. That is fewer cable runs, fewer mounts, and, on platforms that charge per camera, fewer licences. On platforms that do not charge per camera, the licence saving disappears, and the decision comes down to coverage and detail.
This is a product section, so we will be specific.
Dewarping on the client, in the browser. Visylix dewarps fisheye streams in the operator's browser using the graphics processor, over the live video. The server records the original circle untouched, so the full scene is always preserved, and dewarping adds no load on the server however many operators are viewing.
A virtual PTZ view. When an operator opens a live fisheye camera in the focused single camera view, they can switch it into dewarp mode and get a flat view with pan, tilt and field of view controls, from a narrow 30 degrees out to a wide 150 degrees. The dewarping assumes an equidistant projection, which covers most security fisheye lenses.
Plan tier. Fisheye dewarping is included from the Scale plan. Like every Visylix plan, Scale has no per camera charge, so replacing four fixed cameras with one fisheye changes your coverage and cabling, not your licence bill.
Where it fits in the workflow. Dewarping lives in the live focused view, where operators investigate a scene, while multi camera grids, the video wall and recorded playback show the original circle, so the whole room is always one glance away. Visylix analytics run on that full original fisheye stream, so nothing outside a chosen view is ever missed. If a fisheye camera is central to an analytics use case at your site, we test detection across the whole circle, edge included, on your own footage during the proof of concept.
Like everything else in Visylix, it runs on your own infrastructure, including air gapped sites.
Fisheye cameras earn their place in open rooms where the question is what happened here, such as retail floors, lobbies, open offices and waiting areas; when one camera can replace several fixed cameras with fewer cable runs and mounts; where a ceiling mount with no blind spot beneath it matters; and wherever the whole scene needs to be recorded continuously, which no PTZ camera can do.
They disappoint when used to identify people at a distance, for pixel density reasons no firmware can fix; in long, narrow spaces where most of the image circle covers walls; under very high ceilings where people at the edge become very small; in deployments that dewarp only on the camera and discard the original image; and wherever analytics were tested at the centre of the image and then relied on at the edge.
A fisheye camera is a fixed security camera with an ultra wide angle lens, usually 180 degrees, that captures a circular image of the whole surrounding area. Mounted on a ceiling, a single fisheye camera covers 360 degrees horizontally with no blind spot beneath it. Software dewarps the circular image into flat views an operator can use.
Consumer and small business fisheye cameras start below a hundred US dollars. Enterprise models with 9 to 12 megapixel sensors, strong low light performance and vandal resistant housings typically cost from several hundred to over a thousand dollars. The total cost also depends on how many fixed cameras one fisheye replaces, and on whether your VMS charges per camera.
Dewarping is the software process that converts the circular, distorted fisheye image into flat views that look like normal camera footage, such as a virtual PTZ view, an unrolled panorama or a four way split. It can run on the camera, on the VMS server or in the viewing client. Running it on the server or client preserves the full original image for later investigation.
They do different jobs. A fisheye camera records the whole scene all the time, at modest detail. A PTZ camera records only where it is pointing, at high detail. For continuous coverage of an open room, a fisheye camera is better. For zooming in on a live event, a PTZ camera is better. Many sites use both.
Usually not reliably, except close to the point directly beneath the camera. Identification needs roughly 250 pixels per metre on the target under IEC 62676-4, and a fisheye camera spreads its pixels over a whole hemisphere. Use narrow field cameras at entrances for identification and fisheye cameras for awareness of the room.
Typical ceilings of about 2.7 to 4 metres work well. Much higher, and people near the edge of the image become very small. Much lower, and the camera is easy to tamper with and sees mostly the tops of heads.
Yes. Visylix records the original fisheye stream and, in the live single camera view, dewarps it in the operator's browser into a virtual PTZ view with pan, tilt and field of view controls. It is included from the Scale plan, with no per camera charge. Grids, the video wall and recorded playback show the original circle, and analytics run on the full original fisheye stream.