Image Trends - Digital Imaging Products - Fisheye-Hemi Plug-in

Fisheye-Hemi Plug-In

Technology - What is it?

Fisheye-Hemi is a plug-in filter which provides correction for hemispheric fisheye lens distortion.

Fisheye Hemispheric lenses provide a broader view of the world than is possible with any other lens. Until now, the primary correction option available to the photographer was to render these images using rectilinear mapping techniques. These methods have many drawbacks, such as distortion of people and loss of resolution and data.

The Fisheye-Hemi filter provides an aesthetically pleasing and natural view of the image using a unique mapping technology. Fisheye-Hemi provides a more normal view of people when photographed at acceptable distances. It improves the resolution of the image by including more of the original pixels (in comparison to a rectilinear view), displays the intended composition and framing, and straightens vertical lines.

How does Fisheye-Hemi work?

Let’s begin with a basic understanding of what a fisheye lens does and how the eye perceives the information.

Light projects conically into the human eye. The cornea and lens are similar to a fisheye lens. The light is projected onto the curved retina. The human brain uses complex mathematics to correctly interpret the objects that you see into a three dimensional image.

To a person holding a camera, the surrounding space appears to be a sphere centered on the camera. The process of taking a picture projects this sphere inward onto a flat (planar) surface. This surface could be film or a digital sensor representing a planar surface. Fisheye-Hemi provides an improved way of mapping the surface of the sphere to the planar surface.

Figure 1 - Light entering the eye

Figure 2 - Cartographer Map of the Earth

The mapping process has an exact analogy to cartography. Although the surface of the earth is two dimensional, those two dimensions bend into a three dimensional sphere. Ideally this is represented onto the surface of a globe. The cartographer must map the sphere to a flat paper. There is no “right” way to map a sphere to a plane.

In photography, there is still the sphere around the camera, the real world, and still the flat surface of a print or computer screen that must accommodate that sphere with perceived accuracy. In map making, a small part of the globe can be easily flattened on a flat surface. Most lenses cover moderate angles. These images can be easily projected onto a flat surface. Modern advances in optics have given photographers better ultra wide angle lenses, such as the modern fisheye lens. There is a need to better handle the distortions these lenses produce.

Most lenses are “rectilinear”, which means “straight line”. A pinhole camera renders a “perfect” rectilinear projection. With such a projection, a line at any arbitrary orientation maps to a straight line on the print. The radial distance an object appears from the center of the print and is proportional to the tangent of the angle from the normal of the front lens element. With small angles from the normal, this tangential function is nearly proportional to the angle and non-distorting in all aspects. However at larger angles the tangential function grows rapidly, hitting a singular infinity point at plus/minus 90 degrees = 180 degree total angle. For this reason a rectilinear projection can not handle total angles approaching 180 degrees.

Even with more moderate angles of 90 degrees corner to corner, the tangential expansion distorts the aspect of an object at the edge of a picture. For example, with a 20mm lens on a 35mm film camera, a person standing at the extreme left edge of the image would appear almost twice as wide relative to height as if they were standing in the middle of the frame. Because weight is proportional to size, direct measurement of their image would suggest that they had grown from 150 pounds in the center of the image, to 600 pounds if they were at the edge of the image. Often mathematicians define lens distortion exclusively in terms of how straight lines are bent, however photographers know that there are other aspects of distortion.

Some lenses are built to other projections. By far the most common non-rectilinear lens is the equal-solid-angle “fisheye”. This projection is defined such that the solid angle occupied by an object in front of the lens maps to an image with the same area no matter where the object is in the field of view. If used in meteorology, for example, the area of a cloud on the print is proportional to the “size” of the real cloud projected to a sphere centered on the camera, and therefore invariant with respect to the camera aim. This projection does not follow a tangential expansion, and is very comfortable at 180 degrees. Legacy commercial fisheyes have reached 220 degrees, mathematically impossible angles with a rectilinear.

Rather than expanding with a tangential function, the fisheye projection actually compresses progressively with larger angles. For example, if an observer were at the center of a transparent globe showing the earth’s geography, using a hypothetical very wide equal-solid-angle fisheye lens aimed at the north pole, then Australia would appear to expand east-west in the corner of the frame as the lines of longitude were straightened on the flat film, like smashing an orange peal to a flat surface, as they are in a polar map projection. However the fisheye projection would have a concurrent compression in the north-south axis so the area of Australia remained the same on the film. Thus Australia would appear very elongated and flattened, even though the area is correct. In the same way a fisheye lens distorts people standing at the edges by compressing them horizontally and making them unnaturally tall.

A fisheye projection also bends any straight line that does not pass through the optical center. Thus a person appears very tall and thin on the edge of a fisheye image and is bent into a half-moon shape.

For many years, fisheye lenses have been relegated mostly to special effects because of visual distortions. With the advent of wide-spread digital image processing, computer remapping of fisheye lens images is now practical for many photographers, and a number of products are available to “un-distort” fisheye images. However these existing products un-distort a fisheye in a technical sense by mapping to a rectilinear projection. The standard definition of “distortion” is how much lines are bent, and rectilinear is technically a “distortion less” projection.

No matter how mathematically perfect at making lines straight, forcing a rectilinear projection at the extreme angles encompassed by a fisheye creates problems. A major problem is the distortion of people. Further, the extreme expansion of a rectilinear projection magnifies the edge of the image to reveal lens resolution problems. Rectilinear compresses the center of the image which looses detail the lens has been able to capture. Therefore, making images look un-sharp and grainy. The rectilinear projection is unable to map large areas at the edges of the photographed fisheye image within the rectangular bounds of the originally captured image. The result crops out edge detail and makes it very difficult for a photographer to frame and compose in the viewfinder.

In summary…

Figure 3 - Typical Hemispheric Lens

The fisheye lens (depending on the camera sensor size) can typically capture a full 180 degree field measured from corner to corner of the sensor. It is an ultra-wide angle lens. It captures a hemisphere or half of a sphere as seen by the lens:

Figure 4 - Hemisphere of view as seen by the lens

The fisheye lens was originally developed for astronomy to capture much of the sky. They were called ‘whole sky lenses’ in the early days.

A rectilinear lens in photography renders images with straight features (all lines straight) versus being curved. A good rectilinear lens will exhibit no barrel or pincushion distortion.

Definition of Rectilinear Correction – Fisheye lenses can be mapped in software back to a rectilinear space. Rectilinear means that all lines are straight with no curves. Many rectilinear projections will deliver only the center of the full image that was seen by the lens. About one third of the captured information is discarded in this projection. The window demonstrates what most rectilinear projections deliver to the end user. The other information is discarded.

Definition of Cylindrical Correction – Please review the drawing below and recognize the mathematics of a cylindrical projection from a sphere:

Figure 5 - Cylindrical Projection

X= constant*alpha (angle)
Y= constant*Tangent(beta)

Imagine a cylinder wrapped around a globe (fisheye hemisphere in this case) and how the data could be mapped to the cylinder and then rolled flat.

Most projections are ‘distortion free’ only in the center of the projected image. Objects near the top and bottom are distorted. Please refer to Figure 6 representing a typical rectilinear projection. Fisheye-Hemi produces a more aesthetically pleasing image to the average person.

Figure 6 - Typical Rectilinear Projection

A typical fisheye lens delivers images in what is called
‘barrel distortion’ which means that the image appears
to be mapped around all or part of a spherical object.

Barrel distortion:

Pincushion distortion is the opposite of barrel distortion. The magnification of the image increases with increasing distance from the optical axis. This effect typically occurs with low end or poor telephoto lenses.

Pincushion Distortion:

What is different about Fisheye-Hemi projections?

Fisheye-Hemi is designed to provide a mapping function to spatially project an image made with a fisheye lens into an image that minimizes distortion of humans and other objects.

Another design point is to minimize distortion of people and other objects while preserving straight vertical lines and, preserving image detail, It also aids composition in the viewfinder by preserving detail up to the top and bottom edges of the original fisheye image.

What does all of this mean to me?

The human eye likes images to be aesthetically pleasing. You prefer the faces to be normal, the bodies straight, the lines straight, minimal loss of image detail, and high resolution.

Fisheye-Hemi delivers aesthetically pleasing images.

Fisheye-Hemi: It’s for people …

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Tips and Techniques

The Fisheye-Hemi Plug-In installs as a set of Photoshop compatible plug-in filter. It is also available as a separate product for Apple Aperture as a plug-in. Since it is a 'try before you buy' product, you can experiment with your images to see the effect produced. The trial mode watermarks the image.

NOTE: Never save over your original image with any editing software. If you desire to save the image, you should perform a ‘save-as’ function and rename it.

Fisheye-Hemi is a set of simple plug-in filters which requires no user adjustments or interface.

Fisheye-Hemi automatically adjusts for images of different height to width (aspect) ratios, such as 2x3, 3x4, square, etc. The software also automatically adjusts for various resolutions.

Fisheye-Hemi works best with a fisheye lens conforming to the industry standard "equal area projection", which includes virtually all lenses with "fisheye" in the name.

Fisheye-Hemi will work with most full frame lenses on medium format film cameras with the entire maximum image size captured. You are encouraged to try the software with your specific images before you buy it.

Fisheye-Hemi will also work with consumer cameras with fisheye converters when zoomed to a specific focal length. If you see barrel distortion in the Fisheye-Hemi images, zoom towards telephoto, if you see pincushion distortion, zoom towards wide angle to find and mark the ideal zoom setting.

Try taking pictures with the fisheye lens straight on for normal effects. See the difference between Fisheye-Hemi and a typical rectilinear projection. Who is missing in the Photo?

Fisheye Lens

With Fisheye-Hemi

Rectilinear

Try holding your camera at arms length and take a picture. You will be in the picture!

Fisheye Lens

With Fisheye-Hemi

Try holding the camera above a crowd and take a picture.

Fisheye Lens

With Fisheye-Hemi

It will make small rooms look large and people look great.

Fisheye Lens

With Fisheye-Hemi

Take a picture of the interior of your car –especially if you are trying to sell it! It look much larger.

Fisheye Lens

With Fisheye-Hemi

It is also great for sporting events, weddings, parties, and press photography.

You will enjoy the photographic experience without looking through the lens.

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System Requirements

Implemented as a Photoshop compatible plug-in filter or an Apple Aperture Edit plug-in
Supports the following Image Modes:

RGB, CMYK, Lab Color, Gray Scale, Multi-channel, 8 bits and 16 bits

Applications:

Adobe Photoshop 7.0 and higher versions
Apple Aperture 2.1 and higher versions
Photoshop Elements 2 and higher versions
PaintShop Pro 7 and higher versions

Operating Systems:
Windows Vista, XP, NT, 2000

Apple Macintosh OS X and above

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Supported Cameras/Lens

Fisheye-Hemi supports a number of camera and fisheye lens combinations.

Fisheye-Hemi 1 (Circle) works best with a lens and camera combination that covers 180 degrees horizontally across the field, such as a Nikon D80 with an 8mm lens (see illustration below).

Fisheye-Hemi 2 (Full Frame) works best with a lens and camera combination that covers 180 degrees diagonally, such as a Nikon D80 with a 10.5mm lens (see illustration below). This combination is commonly called a "full frame fisheye image".

Fisheye-Hemi 3 (Cropped) works best with a lens and camera combination that covers less than 180 degrees diagonally, such as a Nikon D80 with a 16mm lens (see illustration below).

Below is a graphical example of 3 common fisheye lenses and how various camera sensors map to them:

The drawing above is intended to show the general relationship between the three most common fisheye lenses and various camera sensor sizes. There is no 'wrong' Fisheye-Hemi filter to use for artistic purposes. You should experiment for the effect you find best.

Below are three examples to represent different camera sensor families paired with the three most common fisheye lenses:

The following table recommends which of the Fisheye-Hemi Plug-Ins match your camera and lens combination.

Hemi 1 means the Fisheye-Hemi 1 (Circle)

Hemi 2 means the Fisheye-Hemi 2 (Full Frame)

Hemi 3 means the Fisheye-Hemi 3 (Cropped)

Lens Typeà:	8mm	Nikon 10.5mm	15/16mm	10-17mm Zoom
Camera:
35mm Camera	*	Hemi 1	Hemi 2	Hemi 1-2
Nikon Models - Nikon D1, D1H, D1X, D2X, D2Xs, D2H, D2Hs, D100, D200, D40, D50, D60, D70, D70s, D80, D300	Hemi 1	Hemi2	Hemi 3	Hemi 2-3
Nikon Models - D3	*	*	Hemi 2	Hemi 1-2
Fuji Models - S1, S2, S3, S5	Hemi 1	Hemi2	Hemi 3	Hemi 2-3
Canon Models - 1D, 10D, 2D, 20Da, 30D, 40D, D60, Rebel XT, XTi	Hemi 1	-	Hemi 3	Hemi 2-3
Canon Models - 1Ds, 5D (full frame sensors)	*	-	Hemi 2	Hemi 1-2
Sigma Models - SD9, SD10, SD14	Hemi 1	-	Hemi 3	-
Pentax Models - K10D, K100D, K110D, ist D, ist DL, ist DS, ist DL2	-	-	-	Hemi 2-3
Olympus Models - Evolt E-300, Evolt E-330, Evolt 400E, Evolt E-500, Evolt E-1	Hemi 2	-	-	-
Sony/Minolta Models - Sony DSLR A100, A200, A300, A350, A700	-	-	Hemi 3	-
Kodak Models - DCS SLR/N, DCS SLR/C, DCS 14N	*	Hemi 1	Hemi 2	Hemi 1-2

Table of Cameras and Lenses Combinations

NOTE: * means this combination of camera and lens requires the image to be cropped prior to using a Fisheye-Hemi Plug-In.

Which Fisheye-Hemi should I use?

If your image looks like this; black corners, like a globe in space?
Try Fisheye-Hemi 1 (Circle) for your image.

If your image looks like one of these, dangerous curves, dizzying perspective, but no black edges?
Try Fisheye-Hemi 2 (Full Frame) for your image.

If your image looks almost 'normal', but has some fisheye distortion.
Try Fisheye-Hemi 3 (Cropped) for your image.

What if you click the wrong Fisheye-Hemi?

In art, there is no wrong choice. Each will give different aesthetic effects. You can tell if your choice is not "normal" because vertical lines will bend.

If you select too 'low' a Fisheye-Hemi number, the image will be over corrected and vertical lines will bend outward at the corners of the image (a pincushion effect). Some describe the effect as a renaissance explosion that rivets the viewer's attention on the subject. Try it for artistic effect when you want to grab your audience.

If you select too 'high' a Fisheye-Hemi number, the image will be under corrected and vertical lines will bow inward at the corners of the image (a barrel effect), This is viewed as a circle around the subject. This leaves a hint of the warm, enveloping effect of the original fisheye. Try it for artistic effect when you want the world to circle around your subject.

The Fisheye-Hemi Plug-In works with various fisheye lens converters for consumer digital cameras at specific zoom settings. You should experiment with your camera to determine the most desirable zoom setting for best results, or see the Advanced Tips below for intermediate zoom settings.

This is a 'try before you buy' product. This allows you to try the product with your own specific camera and lens combination before you purchase the product.

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Advanced Tips:

First try Fisheye-Hemi options 1, 2, or 3 based on the Supported Cameras/Lens compatibility chart (below). If you do not get the desired results, then this section will explain how an advanced user can get results between two versions of Fisheye-Hemi. These advanced tips will also apply to images taken with fisheye zoom lenses and fisheye adapters used on non DSLRs.

In general, select the lower number of the two versions of Fisheye-Hemi that you want, giving the stronger effect (e.g.: Fisheye-Hemi 1 is stronger than Fisheye-Hemi 2). Next the strength of the effect can be reduced to the level you want by adding a step before and after the Fisheye-Hemi filter is called, as shown below.

In Photoshop, the first step is to extend the canvas size out in the long direction. For example, with landscape images extend the canvas width, for portrait extend the canvas height. Do not extend both width and height, as this will reduce framing accuracy, and do not resize the image itself, alter only the canvas size. (>Image>Canvas Size, select "relative" and "percent" as options, then fill in the percent increase you want to try, such as 20%.) Second, run the lower number of the two versions of Fisheye-Hemi that you want to interpolate. Third, crop the excess border using the crop tool or canvas size. Through experimentation you will find how much to extend the image to obtain exactly the result you desire. Once you find the exact match, you can write a short script to process many images with the same effect.

A particularly interesting application for advanced users is to use a fisheye lens adapter to get a full hemisphere across the horizon, yet retain portrait quality images of people or animals anywhere in the image. With the fisheye adapter mounted on your camera, find the zoom setting at which the left and right edges of the fisheye hemispherical circle just touch the left and right edges of a horizontal image. Do not zoom out further than this point. At this zoom setting, the image will look like an old fashioned TV set with horizontal top and bottom edges, and curved left and right edges. Then use Fisheye-Hemi 1 (Circle) to unwrap the image. You may need to alter the exact amount of extension or zoom so vertical lines are perfectly straight. You will be rewarded with a most exciting view of the world.

Apple Aperture and the Fisheye-Hemi Plug-In

Aperture is a workflow product that can process single or multiple images. In Aperture, open your fisheye photographs, then select Images > Edit With > Fisheye-Hemi. Now select the appropriate radio button for Fisheye Hemi 1, 2, or 3. Please refer to the Aperture screen shot below:

You can select 'Apply to all' to apply the Hemi 1, 2, or 3 setting you have chosen to all of your selected images. 'Next' takes you to the next image in the selected sequence. Selecting 'Done' completes the process.

Please enjoy your Fisheye-Hemi Plug-In!

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