Rock engravings can vary in size from a few centimetres to many metres. To photograph large designs from directly overhead can be challenging. We use a method of planar mosaic imaging. This involves taking a series of smaller images and then stitching all of these images together to make up a large composite image of the entire engraving. This is similar to photographing a panorama, but instead of rotating the camera around a fixed point the camera is moved in a plane parallel to the rock surface. To ensure successful stitching, each image needs to overlap the next so that the stitching software can find how to align and join the images. Photographing a single engraving may involve taking hundreds or even thousands of these overlapping images.
Setting The Camera
The camera should be set so that the exposure is identical for each of these smaller images. The best way to achieve this is to put the camera into manual mode and turn off any exposure compensation. The focal length, ISO and shutter speed should not change over the course of shooting a series of mosaic images. If your camera can shoot RAW then this is the best option, otherwise shoot at the best quality possible, preferably with a prime lens. A zoom lens pointing towards the ground may change focal length under the influence of gravity or vibration. The camera should be kept the same distance from the rock surface as you take these images. This can be done by reverse mounting the camera under a tripod. A remote shutter release can make things easier when the camera is under a tripod. Avoid placing a foot, your shadow or a shadow of the tripod into any image as these things will prevent the stitching software from being able to join the images correctly. Don’t take too long to shoot the set of images or the ambient light may change or the angle of the sun may introduce unwanted shadows.
If the engraving has insufficient contrast to photograph successfully under the current ambient light conditions then you may want to consider using remote flash.
Photographing
It is better to shoot rock surfaces when conditions are dry. If there has been recent rain and the rock face is wet you may need to use a polarising filter as a wet surface can introduce glare which can reduce detail in the photographs. Very rarely will the ambient conditions be perfect for photographing rock engravings, so be sure to allow for the local conditions and pack whatever equipment you might need accordingly.
Post Processing
If you shoot in RAW then you can adjust the contrast, saturation, sharpness and exposure values before you stitch the images together. Ensure that all of the images are adjusted by the same amount by making the adjustments on a single image and then copy the recipe and paste it to all of the other images in the series. If you are shooting in JPG then make any of these adjustments after you stitch the images together. Many rock engravings are very difficult to discern from the surrounding rock surface and careful post processing is important to achieve successful images.
Equipment
This is a short list of the type of equipment that you might need to successfully be able to photograph rock engravings.
- DSLR camera capable of shooting RAW format
- Large capacity memory card for camera
- Tripod with reverse mount
- 50mm prime lens
- Polarising filter
- ND filter
- Remote flash
- Remote shutter release
- Spare batteries
Canon DSLR Camera
Thank you for this information about what is needed to do reasonable photos. However, what you missed out on, and I would suggest should be included, is two-fold:
1. What drones could be used which would cut the need for a hug number of photos in making the mosaics; and
2. Suitable stitching software for various platforms.
I won’t pretend to be expert in either but I am sure that you would know who to contact for advice.
A number of people have suggested using a drone to help locate rock engravings. We have not yet tried this and we do not consider this to be a very feasible option.
Many engravings are almost invisible without some opportune lighting conditions and can be very difficult to find as the grooves are often very faint and eroded, or the engravings might be located under trees or other scrub. Dappled light or heavy shade can also help to mask elusive carvings. Sometimes we might visit an engraving site a number of times and discover different carvings each time as the lighting changes throughout the seasons. Sometimes we need to lay on the ground and ‘feel’ for the grooves with the palms of our hands and then once located, we can use the remote flash unit to capture an image of the engraving. The number of engravings that could be successfully photographed by a drone would probably be very few, but we would be pleased to be proven wrong about this. Perhaps someone might develop a suitable imaging technique using a drone.
A GoPro type camera on a drone with 4K resolution is 3840 * 2160 pixels. Using this type of setup to capture a 12mt long whale engraving in a single image would equate to just over 3mm of rock per pixel.
Using a DSLR 18MP camera the resolution is 5184 * 3456 pixels and is used at a height of about 1.5m above the rock surface. This equates to around 0.14mm of rock per pixel. This is over 21 times better resolution achieved by using the mosaic method, not to mention the resolving power of a high grade glass lens.
The stitching software that we use is called Microsoft Image Composite Editor (ICE). A large engraving of a whale might comprise of 1500 or more separate images that could take many hours (usually overnight) to composite and render on a desktop computer. Then it might take a bit more time in Photoshop to enhance to a viewable state.