how does the d3dx library save textures to files?

Question

When using the function: D3DXSaveTextureToFile and passing in D3DXIFF_BMP to create a bmp I've noticed that the values seem to be estimated rather than given specifically.

Correct me if I'm wrong but a floating point texture can store any float in any given texel which would put it outside the range of a BMP which is stuck between rgb(255,255,255,255), so what it seems that the function is doing is simply taking the upper most and lowermost value of the texture and normalizing it between that range.

So my question is: Is it possible to grab the values exactly as they are in memory? including when the colours are outside of the spectruc of the computer monitor?

Answer 1

Don't use BMP. Use a format that supports the data type you want. For DX textures, it seems the D3DXIFF_PFM format is what you need. It's described like so:

Portable float map format. A raw floating point image format, without any compression. The file header specifies image width, height, monochrome or color, and machine word order. Pixel data is stored as 32-bit floating point values, with 3 values per pixel for color, and one value per pixel for monochrome.

Note that images will be large, though. A 256x256 texture in this format should weigh in at around 768 KB.

Updates: You should be able to use Image Magick's display command to view images in this format. Also HDRView supports the PFM format. A third choice might be fv.