History - This is a string of characters indicating which image processing functions have peen
performed on the image. The following is the mapping between individual characters in the
string and the operation performed:
@ - Modifications made before history established. 
A - Co-addition of image.
B - Image linearly scaled. 
D - Image dark subtracted.
E - Cool pixels removed. 
F - Flat field corrected.
G - Image smoothed. 
H - Image sharpened.
I - Image pseudo flat field corrected. 
J - Image quantized or posterized to less than 16 bits precision.
K - Warm pixels removed. 
L - Image flipped horizontally.
M - Image flipped vertically. 
N - Image zoomed with pixel interpolation.
O - More than 40 operations performed. 
P - Image log scaled.
Q - Pixels combined. 
R - Image auto dark subtracted.
S - Image zoomed with pixel replication. 
T - Image clipped and filled (ST6COLOR)
U - Image converted to 8 bit log format (ST6COLOR).
V - Image merged to color using 2 color merge (ST6COLOR).
W - Image merged to color using 3 color merge (ST6COLOR).
X - Image translated and back filled (ST6COLOR)
Y - Image pixels inverted. 
Z - Image sharpened with unipolar algorithm.
[ - Image sharpened with one-sided sharpening.
\ - Image modernized by replacing ST6COLOR history characters2
] - Image resampled to make square pixels.
^ - Image averaged.
_ - Constant added to or subtracted from image.
` - Constant multiplied by or divided into image.
0 - (Zero) The history string is set to '0' for new images. This is not a C null
    string, it is actually the '0' character.
a - Image enlarged 2X by pixel interpolation.
b - Image reduced 2X by pixel combining. 
c - Column or Row repair.
d - Adaptive dark subtraction. 
e - Pseudo 3D
f - Auto Dark HPR 
g - HPR Subtract
h - Deconvolve 
i – Median filter image.
j - Set saturation level. 
k – DDP Image.
l – Rotate image. 
m – Fix uncooled TDI image.
n – Fix ME spikes. 
o – Fix blooming streaks.
p – Remove image wedge or gradient 
q – Extract Red, Green or Blue channel
r – Extract Luminance Channel 
s – Rotate image clockwise
t – Rotate image counter-clockwise 
u – Median combine 3 images
v - Rotate image 180° 
w – Image is raw Single Shot Color data