gain and blacklevel's value in VML

I’m studying WordML for Microsoft Word 2003. It uses many schemas and does
VML for processing image data.

As you know, imagedata element has gain and blacklevel as the attributes.

I don’t understand what the two attributes mean and how they are assigned
to somewhat strange value.(like 105703f)

I guess the gain to be image’s contrast and the blacklevel to be image’s
brightness.

As I changed an image’s contrast in Word2003, I saw changing of the
gain’s value in the saved xml file.

Please respond… Cheers…