[X] My Assistant

[CosmicRocker]

I'm still trying to figure out a number of things about the new images we are trying to work with. Assuming others are likewise trying to learn, I thought I would open this thread to create a place for such discussions.

I'd like to start out with a comment about raw image contrast. There have been several postings in the main threads about whether or not the MSL raw images have been stretched like those from the MER missions. I am certainly no expert on this, but it looks to me as if the MSL images have not been stretched at all. I haven't tried to analyze all of the image types, but the hazcams and navcams have pixel brightness histograms that are very different from their MER counterparts.

This attached image compares MER and MSL navcams along with their luminosity histograms.


The MSL images clearly are not using the entire, available range of brightness values, whereas the MER raws do. For this reason, the MSL raw images can usually be nicely enhanced by simply stretching the distribution of brightness across the full 256 value range.

[fredk]

My FFT Fourier filtering is also having serious trouble with the solar shot. One of the other techniques used here will probably work better. Here's my best (quick and dirty) shot, using Fourier filtering at 2, 4, and 8 pixel periods, followed by 2px Gaussian blur. No deBayering at all, since the image uses a monochromatic filter anyway.

You can easily see the asymmetric profile (which you could with MER pancam too).

ADMIN NOTE: A bunch of posts that followed this one, discussing image compression etc, were moved to the MSL Images and Cameras thread.

[mhoward]

But all of the smudginess is artifacts - the sun should be very smooth.

I've noticed that they're really compressing the living daylights out of MSL images before putting them on the web - much more so than the MER images are compressed. Or are we talking about a different kind of artifacting.

[mcaplinger]

I've noticed that they're really compressing the living daylights out of MSL images before putting them on the web...

I think they're just using a fixed quality (75, maybe?). Of course it doesn't help that there is sometimes a decompress/recompress and that they JPEG-compress Bayer-pattern data. The final compression ratio seems to be around 8:1 to 9:1. Are the MER images really a lot lower compression ratio?

For the 100mm sun image, since the filter cuts out all of the pixels besides blue anyway, you'd be better off just tossing the other Bayer positions and then upsampling as desired. But it's still going to be a round slightly-fuzzy circle with a bite out of one side.

[mhoward]

Are the MER images really a lot lower compression ratio?

I've been looking at mostly Navcam images so far, so I guess I can't and shouldn't try to say anything about Mastcam. But for MER Navcam images, the JPGs on the web usually are about 200K or more in size; MSL Navcam JPGs on the web seem to be usually around 100K or less. And there just seem to be more and stronger JPG artifacts, at least in images I've looked at of the deck. That could be factors other than compression for the web; for all I know they're being compressed more heavily on the rover in some cases. All I really know is, trying to take a MER Navcam image and make it about the same file size as the MSL Navcam images we're seeing on the web, I have to use a JPEG 'quality' setting of about 40%, which is high compression.

Here's what I typically see (random section of the image that happens to be in front of me):

Attached thumbnail(s)