1) I checked hdrread in Matlab 2010b, which seems to have ignored exposure time, the code is as follows:
% The formula for transforming (Rm,Gm,Bm,E) into (Rw,Gw,Bw) is given by
% ((Rm + 0.5) / 256) * 2^(E - 128)
rgb = ((single(rgbe(:, 1:3)) + 0.5) ./ 256) .* ...
repmat(2 .^ (single(rgbe(:,4)) - 128), [1,3]);
unsigned char hdr_r, hdr_g, hdr_b, hdr_e;
// -- read hdr_r, hdr_g, hdr_b, hdr_e from the image as unsigned chars.
// Convert the 8-bit HDR RGBE components to RGB float.
float r, g, b, e;
e = ldexp( 1.0f, hdr_e - (int)(128+8) );
r = hdr_r * e;
g = hdr_g * e;
b = hdr_b * e;
which seems to be a little bit different from the above. Still, it doesn't consider the exposure time.
int ee = javaSignedByteToInt(e) - 128 + 8;
double f = Math.pow(2, ee) * WHITE_EFFICACY / exposure;
rgb[0] = (double)(javaSignedByteToInt(r) * f);
rgb[1] = (double)(javaSignedByteToInt(g) * f);
rgb[2] = (double)(javaSignedByteToInt(b) * f);
in which
javaSignedByteToInt(e) - 128
is just hdr_e because in Java, there is no "unsigned" staff.
Where is a documentation to standardize HDR decoding? Well, all the above 3 methods are more or less similar indeed.
Best Regards