Digital image quality. Linear capture.

Light is captured by a digital senor differently to light captured
on film. The way light is captured on the sensor is as a linear
curve which is goes from light to dark. Differently to the way
our eyes adjust the sensor can capture the harsh variances
from very bright to very dark. That means that often the exposure
levels you capture on the camera are darker/brighter than you
perceived.  The histogram shows that linear tonal range in its
shape.

This over or under light capture can be converted using
the "gamma correction curve". This will allow you to
bring the histogram back into a shape that shows both
the highlights and the low lights of the image.

SENSOR LINEAR CAPTURE- exercise.

Objective.

• Take a image and convert it to 16 bits in photoshop
• show the original gamma curve of the image.

         This should show both lights and darks.

• Move the gamma curve to darken the image
• compare the two curves.

The original raw image

I chose this original image that I have taken recently at the Tate Modern
as It had an area of bright and and area of dark.

The original histogram shows that the levels are flat but there is
a peak in the dark tones which is probable the chimney.
There is no highlights or shadow detail that is also lost in this
image capture.

Moving curve to dark

I changed the linear curve as the example stated

changing the curve and moving it away from the mid tones and
moving it into the dark tones has darkened the overall image and
I have lost the detailing in the building.

The histogram has now changed and you can see that the curve
has now moved  towards  the dark tonal range and as now on the
left side of the scale.

Recovering the curve.

I had to mirror the curve above the mid tone range to bring the
tones back to the original image.

It is better to see that I have recovered the image by
looking at the histogram that is more akin to the orginal
raw image. I think I could have made it about 5% more
lighter to be exact.

I then reprocessed the image in photoshop using both
the histogram and linear curve as guidance of tonal
range.

the final histogram shows where I have added light to the foreground
and moved the dark tones closer to the mid tone area of the curve.

CONCLUSION
using the linear curve can add/ recover tonal ranges to the captured
image on the sensor. Look at the curve in conjunction with the histogram
maybe moving the curve can bring back am image to mid tones before
you process in photoshop?