A reader writes:
The image dual images are flipped L/R
The relative magnitudes of brightness are somewhat misleading, since they depend on response of film or of digital camera sensors (which are entirely different, the digital camera being more linear (not perfectly so) over range of brightness, while film in not, but has far greater dynamic range).
In addition, human vision is highly nonlinear (logarithmic in response to brightness), so that it resolves far more contrast in the dark range than in the brighter ranges. So small contrast in the SOT (seen naturally), which is relatively bright with a small contrast image, when inverted becomes much higher contrast when seen. It is not really an effect of camera negative, per se, but of inversion making the contrast more visible by the eye, which is more sensitive in the dark ranges. (This will depend on the re-zeroing of the image as inverted.)
If this was done properly, you wouldn’t use film products. You would employ a 256 bit approx. linearly digital camera to obtain accurate physical information over a linear range.
Then you could decide whether to invert the image for human visualization with higher contrast in the darker ranges (with a suitable zero, for max brightness in the original SOT linear image).
You can confirm all this by using Photoshop, taking photos with digital and film cameras, and inverting the results.
I have always been a little puzzled by the effects of using image obtain by film cameras. Especially if the original NASA 3D program was intended to be used with film as opposed to digital camera images.
You can eliminate all this distortion by histogramming output of a digital image of the original, also comparing to a nearby patch which does not show the image of the body.
And so the digital scan found in the iPad app, Shroud 2.0, comes to mind. To what extent have those images been manipulated for presentation value?
The VP8 Image Analyzer (NASA 3D program?) was used in a variety of applications. Unsure it was created for a certain kind of image. I actually processes the camera input of anything the camera is pointed at, be is an image, a landscape, or anything else like a statue.
” I have always been a little puzzled by the effects of using image obtain by film cameras”
What effects are we talking about ?
Evaluating the image contrast on the Shroud based on “looking” at it is too subjective. As noted by this reader, the human eye perceives contrast by a complex mechanism that not only is not linear (relative to brightness) but depends on the color spectrum. The only objective way to analyze details (e.g., contrast) in an image, as complex as the one on the Shroud, is to use a computer and obviously a digital image. And by the way, I keep being surprised by researchers referring to the VP8 (to analyze the 3D data of the Shroud) because it is an old technology made obsolete by today’s computer and software.