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Holger

photoreal color corrections and watermask

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Hi all:I'm experimenting with free Landsat 7 ETM imagery available at http://geogratis.cgdi.gc.ca/clf/en to use either directly as photoreal or as a basis for high-quality landclass replacements.For the photoreal textures, I merged the panchromatic 15-m band with the three lower 30-m bands as described on John Child's website: http://www.terrainmap.com/rm29.html#HSL . The procedure gives good results and I have been able to display the textures in FS2002. However, two issues remain:1. The merging procedure results in a color shift that is tricky to correct. I have tried various methods in Photoshop and Paintshop (channel mixer, curves, auto levels, etc) but was wondering whether anyone knows of a more formal or efficient procedure? 2. I have no problem making a watermask but the size of my study area makes it impractical to do this for each LOD13 tile individually. I can save the full-scene watermask as a bmp and slice it with resample but how do I batch convert the slices into alpha channels and merge them with the textures? (Christian's tutorial indicates that this might not be possible but I'd like to double-check with the experts).Thanks for any pointers. Cheers,Holger

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Hi Holger.Go to:http://www.terrabuilder.com/And look for 'Resources/Support Apps' and find Elrond Elvish's "FSTexConvert" ( it also requires Martin Wright's support *.dll files ). This should allow you to slice and merge a watermask to the LOD13 textures.Dick

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Holger, it sounds like the base image is sufficient but greyscale, and the remainder of the referenced procedure is to provide color. yes? And the problem you face is to correct the color?I use a simple procedure to produce color, which I find sufficient. I take my grey scale image and superimpose layers of greens and browns at about 50% transparency each over top, with the color layer set to show at specific bands of greyscale background value. By adjusting these values, with thoughtful overlaps, you can get a pretty nice image. You can also add yellows and reds, although the background value discrimination within the grey scale image is a bit splotchy for that to work real well. I use two colors of green, two colors of brown, and then take a copy of the roads in grey scale and move that copy to the top.Rhumba has the right answer for batching your alpha slice with your image slice. Elrond's utility is the best.Bob Bernstein

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Hi there:Dick, thanks for the link to Elrond's utility; looks like it'll do the job I need done!Bob, actually the merged Landsat scene is in color but the inclusion of the grayscale band as the lightness band leads to color shifts as shown in the two images below (top is a true-color RGB of bands 3,2,1 (30-m resolution); bottom is after merging band 8 (15-m) by means of the HLS transform). The high elevations don't look so bad but the lowland forests and mid-level meadows are quite off.However, your description of coloring a grayscale image gave me the idea of using Band 8 directly; I'll try your method and post here if I get useful results. BTW, I have since found your more detailed description in an older post; the first time I tried to find information via Search I used "grayscale" instead of "greyscale" ;-)Any further advice on dealing with the color shift is appreciated (though I may not need to deal with it).Thanks again. Cheers,HolgerP.S. Note the neat differences in water colors in the top image due to different sediment contents.http://forums.avsim.net/user_files/36031.jpghttp://forums.avsim.net/user_files/36032.jpg

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