Quote:
Originally Posted by aurora
I see two different amounts of shading.
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aurora, I think that you and Jon may have misunderstood what I meant when I wrote that "Normal 3D shading cues were aggressively suppressed."
What I meant by "normal 3D shading cues" was this: large-scale variations in brightness, which allow a normal human visual system to perform a kind of "shape from shading" process, and thus perceive the three-dimensional shape of the landform.
What I meant by "aggressively suppressed" is that these large-scale variations in brightness, which serve a very important purpose in helping a normal human viewer to perceive the 3D shape of the landform, were _selectively_ eliminated from the image. Smaller-scale variations, which help the viewer to perceive the shape of small lumps and boulders, but which do not help the viewer to perceive the overall 3D shape of the landform, were _not_ eliminated from the image.
To help you understand this, I'm attaching a new animation to this message. This animation was prepared in the same way as "before-after.gif" above, except that instead of including the entire image reduced in size, this time I've extracted only a small square, and highlighted an important 3D feature.
This animation shows a small lump or boulder (informally known as "the teardrop"), and the approximately level surface (or "platform") on which it lies, and the slope below the platform, and the approximately level plain below the slope. The slope is highlighted.
If you look at the animation, you'll notice that in the original raw image the platform is brighter than the level plain, and much brighter than the slope. This phenomenon is of course caused by the position of the sun in the sky, and by the shape of the landform. This large-scale variation in brightness helps the normal human viewer to perceive the 3D shape of the platform, and the slope, and the plain.
When you look at the animation, you'll also notice that in the image that was used in the press release, the difference in brightness between the platform and slope and plain has been very aggressively suppressed. There's almost no difference. It's much more difficult for a normal human viewer to perceive the platform, and the slope, and the level plain.
Does this suppression result from a simple reduction in contrast?
No!
Look at the "teardrop." Like other small lumps and boulders in the image, the teardrop's 3D shading cues are actually _more_ prominently visible in the press release image than they were in the original raw image that was returned by the spacecraft.
In summary: the overall shape of the landform was suppressed, while the shape of individual lumps and boulders was enhanced.
Quote:
Originally Posted by aurora
In reading this thread, I have to say I am unable to discern why you are in such a twist about this. Seems to me like you are trying to make something out of nothing, which makes me think you must have some sort of agenda.
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No hidden agenda. I had an interesting result in forensic image analysis, and wanted to share it. Contemplation of the implications of that result led to an interesting object lesson in the Ethics of Bad Astronomy, so I decided to share it here.
Most of my followups in this thread have just been clarifications for people who are confused about the basic facts, e.g. which image was returned by the spacecraft, and which image was used in the "catbox" press release.
Trying to make something out of nothing? Pshaw, I'm only doing what this site was designed for. We find clueless misrepresentations of real astronomical data, and we criticise them mercilessly. Right?