It's after 3 am (in UK time) and I couldn't get to photoshop yet to try to go through the chain of work. However, There's one plug-in tyhat may actually be quite useful in what you're aiming to do.
DDS Photoshop Plugin + NVDXT ToolsIts READ Me says (in extractions) :
"This program compresses images,
creates normal maps from color or alpha,
creates DuDv map
creates cube maps
writes out .dds file
does batch processing
reads .tga, .bmp, .gif, .ppm, .jpg, .tif, .cel, .dds
filters MIP maps
Options:
-nomipmap : don't generate MIP maps
-fade : fade MIP maps
-browse : browse for directory
-dither : add dithering
-timestamp : Update only changed files
-list <filename> : list of files to convert
-cubemap <filename> : create cube map <filename>.
Files specified with -list option
-all : all image files in current directory
-outdir : output directory
-file: input file to process
-swap : swap rgb
-binaryalpha : treat alpha as 0 or 1
-alphaborder : border images with alpha = 0
-fade : fade map (color, normal or DuDv) over MIP levels
-fadeamount : percentage to fade each MIP level. Default 15
-fadecolor <hex color> : color to fade to
-fadealpha : fade alpha over MIP levels
-border : border images with color
-bordercolor <hex color> : color for border
Texture Format options. Default DXT3:
-dxt1c : DXT1 (color only)
-dxt1a : DXT1 (one bit alpha)
-dxt3 : DXT3
-dxt5 : DXT5"
Download and more info from here:
(Filefront/Elite Force 2)
http://eliteforce2.filefront.com/file/D ... 69x#148888=============================================================================
Lets see if it can do what it claims on your case, too.