Using hires mars maps

[Mahnmut]

Hello again,
I am back with my old problem:
where to get the best Mars hightmap and how to use it?
The best planetwide map I can find to date is that one:
https://astrogeology.usgs.gov/search/map/Mars/Topography/HRSC_MOLA_Blend/Mars_HRSC_MOLA_BlendDEM_Global_200mp_v2
200 m per pixel for a whole planet, thats a lot of pixels, 11,4 gb of them actually. The biggest maps I can load into TG on my computer are 2 gb.
So I can use parts of that map, so far so good.
Now there are two problems:
1- the map appears to be "partially inverted" meaning the lower half is brighter thann the upper half, but inside each half the greyscales are in the right order, so I cannot simply invert it. Hard to explain. where the greyscales representin hight should be 1-2-3-4-5-6-7-8 they are 5-6-7-8-1-2-3-4?
I tried a lot of tricks in photoshop, making masks to adjust the displacement, and it works quite, but there are always strange artefacts, pixel sized in the best cases, along the border.
Any ideas?
2 may be easier:
how can I place my partial maps on the planet?
using a planetwide equirectangular map is easy, project it spherically and there you go. But how can I put a quarter, or some rectangle from the middle of that map on top of a lowres planetwide map in the right place?
Thanks in advance,
would be great if somenone could help.
Best Regards,
J

[Mahnmut]

Well, I found a solution to the "inversion"-problem.
1) use the magic wand selection tool in photoshop to select the bright part of the map (the border between the parts has high contrast, so no problem) and fill it the former bright part solid black. Save file.That one has the higher elevations on a flat base
2) repeat step one with the original file, invert selection and fill the former dark part solid white. Invert the whole thing, save a second file. That one has the lower elevations with negative values now, no displacement for the high areas.
3) use the first map as Displacement wiht a positive value, the second one with negative value.
Et voilà !  so to get from (5-6-7-8-1-2-3-4) to ( 1-2-3-4-5-6-7-8) , I take -[-(1-2-3-4-0-0-0-0)]+ (0-0-0-0-5-6-7-8), if that makes sense. The double minus is necesary to create a black =zero displacement area for both halves.

[Mahnmut]

Now my next question is, what is the limit to imagemap size? I do have 32gb of ram, still TG crashes every time I try to load a map bigger than 2gb, while several maps of 2 gb load slowly, but without problem.
Just ocurred to me this  moment, is it the grafic card? never thougt of that one?
Is a tiff-file of 11gb a "bigtiff" or just a big tiff?
Best Regards,
J

[Hetzen]

You're churning a lot of data there. The Tiff format should be in floating point values, so can have positive and negative values beyond the colour range of .jpgs. They will also have a linear value range, where as .jpgs will have a gamma curve on it's grey scale, which will mess about with the proper height values (unless that's been accounted for in the jpg creation).

Map Tiffs tend to be in GeoTiff format, which has projection and placement values in the header file. Messing about in Photoshop and saving back out destroys this data as PS doesn't write it back into the file. That said, you can crop this down into smaller bite pieces. So have a 2gig overall map, then crop out a higher res version on the area that you want the detail. You'll have to figure out how you'll place that back on the planet sphere. A soft edge mask around your hero image will help disguise any miss alignments.