The philosophy is that a scientific image isn't a scientific image unless it has a scale of measurement built into the image. Here then are some ideas for building measurement scales into 3D images. (Also, the opening chapters of Visual Explanations and Beautiful Evidence, provide examples
of scaling of 3D images.)
Call out a specific element, via annotation perhaps, and state its size. The call-out should
be imbedded in the image.
Tie an object of known size to the image. For example, the diameter of Earth isn't all that
much greater than the Cassini division. That tells a lot about Saturn's size; also the Cassini
division shows a foreshortening perspective effect and thus the scale is carried around
Saturn in perspective.
Show the changing size of the Earth dot at a number of prominent locations in the depth
Imbed some text about size into the image itself: for example, the diameter of Saturn is
about 120,000 km or 75,000 miles. Or 00000 Earths would fit into Saturn.
Place the Earth dot on Saturn.
If one dimension is stretched, show the original unstretched image and the stretched
Center a 3-dimensional scaling tripod at Saturn's center.
Allow viewers to flip back and forth between a scaled and unscaled image; or place them
Retain scaling during zooms; might well use contextual zooms.
All the scaling lines should be thin and graceful. Don't worry if now and then the
background washes out a faint gray dimension line.
Indicate color shifts due to optimized false color. There's probably no such thing as true
natural color but some colors are closer than others. Show multiple colorized images to
give viewers some sense of color variation resulting from Photoshop.
Do at least as much Photoshop (+Illustrator) work on showing scale information as is now
done on colorizing, one-dimensional stretches, and collaging various images into one
For human-size objects, place the Lascaux hand stencil or the Pioneer plaque people
nearby as appropriate.
Use logarithmic scales when appropriate.
Build scales that can be photographed into vehicles that explore other planets, just as an
archaeologist places a meter stick or a hammer in photographs.
Have exploration vehicles on other planets leave a measuring-tape trail behind that appears in at least
some photographs of the planetary surface under exploration.
There are surely exemplars from architects, perspective theorists (who place humans at
various distances in perspective drawings), and astronomical photographs.
Early on in the text accompanying images provided several ways of thinking about the
scale and location of the imaged objects.
Imbed basic scaling information in the image itself; otherwise scaling information may well
be dropped as the image is reproduced and distributed.
Don't let the PR staff or communications experts or similar have any control at all over
built-in image measurement scales or any other image-processing moves. Use the excellent
technical tools of graphical design to create the scaling information but avoid the attitudes
of designers or commercial artists. Quantitative documentation of images is a matter of scientific integrity and teaching about measurement, not
pitching. Astronomical images don't need pitching.
There are difficult technical issues of graphic design in showing scales of measurement: the images have very high apparent resolution compared to clunky-looking typography and jagged lines placed near the images. There needs to be a lot thoughtful design work to imbed scales of measurement successfully into the beautiful images. The scaling devices should be in the background and often on the periphery of the image to avoid the thick-pencil clunky look of many measurement scales. Elegant scaling of images will require investments at the level of current investments in image processing, colorizing, collaging, and other now-routine manipulations of images.
Systematic built-in documentation of images provided to the public is part of NASA's teaching role: scientific work not only shows things but also measures things. The endless stream of beautiful but dequantified images suggests that scientific research is merely about image-making, not measurement. NASA should raise the level of scientific discourse--and should avoid pandering to the prevailing dequantification in pop astronomical imaging.
It is essential that basic measuring scales be built into the images themselves, so that quantitative documentation is persistently maintained throughout the chain of image reproduction in newspapers, the internet, television, and astronomy textbooks. If basic quantitative documentation is placed in text separate from the image, the documentation will often be dropped in the process of reproduction and distribution of the images.
Some of the most interesting material in astronomical imaging is often the sizes, location, and context of the image.
Perfection is the enemy of the good in setting scaling rules. There's is already a big gain in
just having rough approximate scaling compared to no scaling. Settle for being
approximately right, rather than foregoing scaling because it is not exactly correct.
One image can't do it all.
-- Edward Tufte