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Originally posted by qmantoo
The point is that it is not just any old cross, but is symetrical, so it is unlikely to be as a result of a compression or contrast adjustment algorithm..
To have a rogue area in the middle of a large block of 'shadow' which shows up as a cross is unusual.
In a gif from the pds, it is unlikely to show as these have been balanced and the greyscale values are evenly distributed, however, if there are any areas of pure black, they will show as red in this processing from my program.
If, as you suggest, it is the result of JPEG compression, why are there no more compression artifacts or non-zero greyscale values within the black 'shadow' area marked in red?
The fact that it is symmetrical is what makes me think of a compression artefact (that and the fact that it's not the first time I see one of those). Whenever you see something that fits perfectly in a 8x8 pixels square in a JPEG image then it's very likely to be a compression artefact, as JPEG uses 8x8 pixels squares to make the compression.
Originally posted by qmantoo
If, as you suggest, it is the result of JPEG compression, why are there no more compression artifacts or non-zero greyscale values within the black 'shadow' area marked in red?
Although you have put up a feasible explanation, it does not explain why it is the only non-zero set of greyscale values within the fairly large expanse of 'shadow'.
I think it is unlikely you are correct in this instance and so I do not think it is caused by the JPEG algorithm.
Originally posted by qmantoo
As you say, this cross appears to be a JPEG artifact, however, I have to say that in light of the difficulty of obtaining any detail from it(see below), I suspect that it may have been marked with a cross for censorship. Of course, that is pure specultion.
To bring controvercy into this, the shadow area is not showing shadow from the sun shining on a rock at all, but is some kind of black colour which has been placed there.
Originally posted by qmantoo
Yes, the image was of poor quality,. but I can handle that.
How do you know that?
What I cannot handle is the black areas which are definitely not on the original which came down from Mars.
How do the scientists see anything useful in those images and why dont they complain about it?
Or more to the point, why dont they ask why it has been blacked out?
How do you explain those areas then - or is that not a subject you want to discuss?
How do you know that?
So who gets to look at these 12-bits per pixel images? Where do they get them from - certainly, they do not get them from the pds like we can. If the PhDs at our universities are writing scientific papers based on this absolute poor quality then I do not think our science will progress very far.
I think that the images are 12 bits per pixel images, so they can work with more than the 8 bits per pixel of the PNG or JPEG files.
I really cannot say if "the scientists" (who are these scientists who get exclusive access to 12-bit images?) have seen these images before they were blacked out or censored. However, I do believe that we dont get access to the best quality images which are available.
Now you are assuming that there was an area that was blacked out and that it was done before the scientists have looked at the images.
Ha! where have you seen shadows on Earth like this? (see the first paragraph of this post)
Shadow.
Originally posted by qmantoo
All I get is a black image, was I supposed to see something else?
I know that the black areas are not on the original because (as I explained) I can see half-features on the rock which are just outside the border of the black censored area.
If I'm not mistaken about the 12 bits per pixel images, that's how they are captured by the cameras on the rovers. I have to look again at that, I may be giving you wrong information.
So who gets to look at these 12-bits per pixel images? Where do they get them from - certainly, they do not get them from the pds like we can.
Looking at the png you posted earlier, the border between land/sky does not show any pixels and has STILL got compression artifacts over the whole picture (although they are a different type).
I really cannot say if "the scientists" (who are these scientists who get exclusive access to 12-bit images?) have seen these images before they were blacked out or censored. However, I do believe that we dont get access to the best quality images which are available.
Ha! where have you seen shadows on Earth like this? (see the first paragraph of this post)
Each rover has a total of 9 cameras, which produce 1024-pixel by 1024-pixel images at 12 bits per pixel,[39] but most navigation camera images and image thumbnails are truncated to 8 bits per pixel to conserve memory and transmission time. All images are then compressed using ICER before being stored and sent to Earth. Navigation, thumbnail, and many other image types are compressed to approximately 0.8 to 1.1 bits/pixel. Lower bit rates (less than 0.5 bit/pixel) are used for certain wavelengths of multi-color panoramic images.
ICER is based on wavelets, and was designed specifically for deep-space applications. It produces progressive compression, both lossless and lossy, and incorporates an error-containment scheme to limit the effects of data loss on the deep-space channel. It outperforms the lossy JPEG image compressor and the lossless Rice compressor used by the Mars Pathfinder mission.