Gigapixel Imagery. An introductory guide to the photography, the creation of panoramas and interactive virtual tours.

Comisiwn Brenhinol Henebion Cymru Royal Commission on the Ancient and Historical Monuments

of Wales

Louise Barker & Fleur James

louise.barker@rcahmw.gov.ukfleur.james@rcahmw.gov.uk

A Gigapixel image is a digital image composed of one billion (109) pixels (picture elements) (1000 times the information captured by a 1 megapixel digital camera). Current technology for creating such very high-resolution images usually involves making mosaics of a large number of high-resolution digital photographs to create panoramas.

A panoramic view of Aberystwyth: comprising a mosaic of over 400 images. The creation of one high resolution image enables you to zoom in to view information in great detail.

Robotic Camera Mounts: Available for a range of cameras. The Gigapan (www.gigapan.com) products include the EPIC series and cover compact digital cameras, point and shoot and DSLR. These range in price from £200 - £700

Manual Camera Mounts: These can be cheaper but the mount needs to enable the camera to be rotated horizontally and vertically around the camera/lens nodal point. The mount also needs to have markers/increments so images are captured at equally spaced intervals.

GIGAPIXEL PHOTOGRAPHY : THE HARDWARE

Simply attach your camera (up to 4.5kgs) and the EPIC directs you through the steps to capture a Gigapixel image. You’ll need to set the focal length and then the upper left and lower right corners of your panorama (anything up to 360° horizontal and 180° vertical), after which the EPIC will calculate the number of photographs to be taken and time it will take. Once started the process is automated, the robotic arms turns on a set path and triggers the camera at each stop.

GIGAPIXEL PHOTOGRAPHY : THE EASY BIT

The EPIC does have a number of different on-board options to change settings. Including•Picture overlap: anything from 25% to 75%.•Stationary time between movement (up to 1 minute). This depends on your chosen camera settings and the exposure times.•Pre-trigger delay (up to 3 seconds). Allows camera to settle before the shutter is triggered•Multiple triggering option - allows it to take up to 20 pictures at each image location for exposure bracketing or multiple image enhancement.•Picture order: columns or rows; down or up; left or right.•Aspect Ratio. Generally 3:2 but this can be changed to suite your equipment.

Things you need to consider before you start, that will have an impact on the photography:•the subject of your photography•the requirement of your finished product •the time you have•the processing power of your computer

GIGAPIXEL PHOTOGRAPHY : THE NOT SO EASY BIT

We trialled a number of different camera settings for the ‘Digital Dissent’ project which involved interior and exterior photography of chapels.

After trial and error we stuck with the following:

•28-35mm focal length•Manual fixed focus (on a few occasions it was possible to use autofocus)•Aperture Priority setting : F11-F18 at ISO 800-1600 with variable shutter on auto exposure

For 360° panoramas this resulted in a time of roughly 1 hour to take and capture around 400 photographs.

Focus: Autofocus is not reliable in areas where there is little or no differential of density for the cameras focus sensor e.g. blue skies or plain interior walls. The camera will spend all its time trying to focus and the shutter will not be triggered before movement takes place. This will result in gaps in your panorama and a headache during processing.

To avoid this focus the camera manually and use the Aperture priority setting, using the smallest aperture possible to maximise the depth of field.

Lighting:Interior photography would normally require complex lighting to achieve a natural look and a bank of lights would be needed from outside the panorama. Moving lighting around would result in cross shadows and lighting within the panorama can cause an obstruction.

To avoid this use natural lighting from windows and interior lights. Set the camera on auto exposure (aperture priority) to capture the maximum information available . Before you then start the panorama, if using a robotic head make sure the time/exposure setting as on the Gigapan EPIC is set for a longer period of time than the longest exposure required.

GIGAPIXEL PHOTOGRAPHY : some handy tips

Camera Settings: Auto exposure, aperture priority F16; 35mm focal length; fixed focus. Gigapan EPIC settings: 30% overlap of frames; with an estimated maximum shutter speed of 3.5 seconds on the camera, a 6 second time/exposure setting.Product: 400 images, taking 1 hour and 6 minutes to collect.

Peniel Chapel, a 360° panorama of the ground floor.

Lens choice:This will depend on the distance between the camera and the subject and the amount of detail. A longer focal length (i.e 75mm compared to 35mm) = more photographs = more time = more processing = a larger file.

Wide angle and fish eye lenses can be used = less photographs = less time = less processing = a smaller file, but the quality and detail will not as good and there will always be a certain amount of distortion.

http://www.welshchapels.org/peniel/tour/

Using Pause:The Gigapan has a pause function that can be used when dealing with moving objects, such as cars or people entering the panorama. Due to the nature of overlapping photographs, one photograph of a moving object is unlikely to result in a solid form but more of a ghost effect.

It can also be used to wait for the sun to go behind the cloud when in shot to prevent flare and an unusable photograph.

There are a number of different software options available and some free downloads: Photoshop, GigaPan stitch, Panoweaver, PhotoStitcher or Kolor Autopano Giga (€199)

Kolor Autopano Giga has the following useful features:

•advanced stitching engine, no need to specify the order of images, instead it launches detection and finds relationships through software•auto correction of moving objects (anti-ghost), allows you to keep and discard objects •enables the user to take over manual editing of control points that forces software to add links between images •automatic colour and exposure correction and anti-haze filter•range of projections e.g. if 360° cylindrical or spherical projection, (maintain rectilinear for architectural monuments)•export – render out panoramas: JPG, PNG, PSD, PSB, TIFF; •batch rendering of multiple panoramas•the creation of panoramas using images not taken from same perspective e.g. aerial photographs

CREATING THE PANORAMAS: stitching your images

THE PROCESS

Select your images and then allow the software to carry out detection to create an initial panorama. You can either use the pre-set detection parameters or specify your own. This process is quite short (it takes about 2 minutes for 182 images) and at this point lens distortion and colour equalisation is also undertaken.

The edit screen provides information on the stitching quality and allows you to make changes to the image such as rotation and cropping.

You can also look closely at the detection and the relationships the software has chosen

In CP editor you can look closely at the relationships and add and delete control points manually

It can still go wrong…..but the software has enough options for you to be able to put it right

Once you’re happy with the image, it needs to be rendered to create the final version. File formats include: JPG, PNG, PSD, PSB, TIFF.

Be warned! This is both a time and processor consuming process.

THE END PRODUCT

The final rendered image will be a large file. The above panorama, comprising 426 images, was rendered as a .psb file (Photoshop big file) and was 4,681,469KB in size. A PSD/PSB file is larger than other file formats (jpeg/tiff) as it contains more information. This was important for us when producing the virtual tours. But you might want to consider a different format that creates a smaller file but don’t forget your file format and size will also has archive implications.

CREATING INTERACTIVE VIRTUAL TOURSOne product that can be created from gigapixel imagery are Interactive Virtual Tours. We created 4 for the ‘Digital Dissent’ project and they are available to view here www.welshchapels.org/

We used Kolor Panotour Pro (€300) to create the virtual tours. The software allows you to:•create and customise 360° views.•add hotspots and embeds sounds and videos, PDF files, pictures, websites.•allows you to share your virtual tours on all devices (computers, tablets, smartphones). and is compatible with Mac, Windows, Linux

You can customise your view and styles used.

The final task is to ‘build’ your tour. Another time and processor consuming process

The end product is a .html file that works with a folders of tiles. Tiles are jpegs created from the Gigapixel panoramic images, that have been chopped into a series of smaller files, used and loaded as you zoom in and out of the tour. Be careful not to make your final tour too big. For each of the four chapels we aimed to create a product less than 800MB.

http://www.welshchapels.org/bethania/tour/