The nice thing about digital SLR cameras is their ability
to shoot in raw format. Using the Fuji S2 Pro,
it is possible to convert raw files, using Fuji
EX, into exposures that are 1 stop under to 1,2, or 3 stops
over. The nicest thing about all this is that this exposure
"bracketing" can be done AFTER the fact and without losing
luminance or chrominance information!
1- With the S2 take a picture at ISO 100.
2- After downloading into the computer, use EX to convert to a
tiff file using normal sensitivity.
3- Then convert this same file AGAIN, this time correcting for the
blown highlights (-1)
4- You now have two tiffs of the same file that are named
DSCF0520.tif and DSCF0520_1.tif.
5- Notice that each time you convert, EX assigns a new name by adding
a _1, _2, etc.
6- Now open both tiff files in Photoshop. Make sure they are in 8 bit
mode (if not, change them).
7- Drag the "normal" exposed photo onto the
"under" exposed photo.
8- Make sure "snap" is checked (View,
Snap). The images will align pixel for pixel.
9- Using the eraser tool, erase all the blown highlights. The darker
highlights will now show through. Magic!
10- Of course you can also use any selection tool, feather, and cut.
11- Using this same technique you can see how the range can be
greatly increased - even to 4 stops.
12- Using ISO 100 effectively gives a sensitivity range of 50 to 800,
a range the S2 handles quite well and with very little noise. In fact,
this is a strong point of the S2 over some Nikons and Canons.
Here is a very crude example of how exposures can be combined. Please
note that this same effect can NOT be done in Photoshop by simply using
one photograph and dodging and burning, etc. Even using 16 bit files.
The information simply is NOT there.
Normal Conversion (blown highlights)
Highlight Conversion (the rest is too dark)
Combined Normal and Highlights (took only a few minutes simply to
show the principal)
Of course you can also save blocked shadow detail the same way, only
combine with a +1, +2, or +3 raw conversion. If you are extremely
skillful, you can turn the Fuji S2 6+ stop range into a 10+ stop range!
Sometimes I use 3 separate conversions of the same image.
Again,
you can NOT simply use levels and curves to produce a similar
range.
For the Technically
Inclined
Here is the scientific explanation of what is
really happening. These charts were provided by Sokolov Mikhail as
published in http://www.fcenter.ru/.
CHART
1: For gray card and multiple
images with different exposures, S2 can provide 10.6 EV useful latitude
(9.1EV linear latitude and 11.6EV full latitude) for ISO 100, RAW
(metering directly from the RAW data).
CHART 2:
ISO 100, JPEG: useful latitude about 6.8EV (6.0EV linear, 7.7EV - full
latitude).
More importantly, this technique does expand the range.
The extent is limited purely by the amount of noise that can be
tolerated in any given photograph. In the
photographic example above you can see that just one additional stop
made a huge difference.
