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Recording Rock Art -- Getting More Information from Digital Images

Recording Workshops

Manual recording will always remain indispensable for accuracy, especially for examining very fine incisions, for checking which rock art is superimposed over which other rock art, and for comparing relative patinas and other matters.  Drawings can be much easier to understand than photographs, yet photographs can record details that no artist would take the time to record.

How to get good photos in general – helpful techniques

Visitors to rock-art sites want to take home pictures of what they have seen.  Pictures are of course the only thing we should take, and we should leave no traces of our visits.

One way to get better pictures is to have a longer time to visit, to come at different times of day when the Sun is at different positions, so the rock art is in sun or in the shade, or so the light is coming from an oblique angle (especially good for revealing light incisions).  When we cannot do this, a friend can sometimes hold a portable sun-protector of the type used in car windows (or in a pinch, an umbrella) to give uniform shadow across an entire motif or scene.  Be careful these objects do not touch the rock art.  In darker moments, a friend may hold a flashlight at an angle.  A polarizing filter can also reduce glare from the Sun.  Additional hints for photographic techniques can be found here.

Digital Photography and Technical Manipulations Mean More Rock Art

There are an increasing number of sophisticated technical means to enhance digital photographs to reveal what is not visible to the unaided eye.  The first two mentioned below increase the contrasts in digital photos.  Because we have these new tools, there is now more (recoverable) rock art in existence than there was before the tools were invented.  It exists even on many rock surfaces where nothing seemed to be present when we looked at it simply with our eyes. Some of the programs mentioned below are commercial, and there may be alternatives to accomplish the same tasks. If visitors to our site know of others, please let us know via the comments button below.

PhotoShop™

Here are the most basic operations to adjust contrast. From the "Image" menu of Photoshop, choose "Adjustments [Levels]", then move the right and left slider triangles to get the best contrast possible, going back and forth between them. Approve the best choice for your purposes. If the adjustments were large inward movements of the sliders, you will notice some exaggeration also of color contrasts. If you wish to eliminate much of that, do the following carefully with no other operations intervening.  Go to the "Edit" menu, choose "Fade [Levels]". From the dialog box which opens, click on the drop-down menu (which may say "Normal"). Go to the bottom and click on "Luminosity".

{To refine further, producing an image with a bit more color: Select the entire image and Copy the image with faded luminosity. Go back steps in the "History" panel to the point just before the "Fade [Levels] operation, where the color was still exaggerated.  Paste the luminosity-"faded" image (as a new Layer).  In Layers, adjust the transparency to mix the luminosity-"faded" image with less color and the image with exaggerated color in whatever proportions are most satisfactory.}

Much more interesting results can be achieved by adding and subtracting color components of an image, increasing contrast along particular color dimensions.  This can be fine-tuned.  Here is a published paper on methods scroll down to "Computer-Assisted Photographic Documentation of Rock Art".

DStretch

This software program does some of the manipulations which are done by hand with Photoshop, simply by clicking on a button.  That is an advantage.  A disadvantage is that this program does not preserve original colors, it changes them as well as increasing contrasts.  Here is a detailed description of DStretch http://www.dstretch.com/.

RTI -- Pseudo-3-Dimensional stitching of multiple digital photos

Digital photos taken from different angles, but with a known object in a constant position for each, can be stiched together by software into a 3-Dimensional image.  Here are more details.  Here is a more information on RTI.

Laser 3-Dimensional Scanning

This is another technology, recently developed, requiring specialized equipment. Here is a Smithsonian web site exemplifying one use.

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