I was remaking some very old maps from 2006 when I noticed
that they used sky_borealis01 and sky_wasteland02 skybox
textures present in HL2, which they were unused and of course, they don't have an HDR version
So aside of adding HDR, I did the "optimization" that it was started on The
Orange Box: instead of having a full 512x512 sized texture knowing that the lower half will be rarely seen, I made them have only the upper half and strech the rest so
their sizes are less than the originals, as well as making the down
textures to be just 4x4 big ( since those are even more rarer to be seen ). However since the borealis texture has a sea at the lower half, I
did an extra version on full size just in case someone needs it.
The pack includes not only the VTFs and the VMTs, but also the core files so people can work directly on them.
Valve made those so I only take credits to fix stuff, feel free to use them on your mods and further improve them.
Disclaimer: As you will probably imagine sky_borealis01 texture is
really old so even on BRGA8888 format you will be able to see pixels,
probably someone decent with 2D art could attempt to solve this as giving a
light gaussian blur makes it look worse later when porting to VTF.
Disclaimer 2: In case someone asks why at the txt files that reads VTEX I
didn't used skybox 1, is because apparently it doesn't work with
different texture sizes. However it is not really important as it only
adds the Clamp T and S flags automatically to the VTFs.
"HDR" and "LDR" folders contains the core files to edit them, but if you only want to use the fixed textures on your map, just get the files that are at the "Done" folders and drop them in your game-mod directory -> materials/skybox folder.
"sky_borealis01-opt" folder contains the textures of sky_borealis01 optimizated to 512x256, while "sky_borealis01-original" contains them at full 512x512 size.