Tuesday, 28 February 2012

Sensor linear Capture

In this exercise I am investigating how the camera sensor captures the image and the processing that is carried out by the camera to make the image more acceptable to us.

The camera sensor captures the image in a linear fashion which results in a very dark picture. We can mimic this by applying curves to a sample picture. The picture has been converted to 16 bit to avoid any image 'banding' that may happen if we process this as 8 bit.

Here is the image as it came from the camera. Note that the histogram has a good spread of tones.

The picture straight from the camera.

Now compare the image above to the one below that has been adjusted to resemble the linear capture from the sensor. This has been done by applying curves.

How the sensor captures the picture.
All the tones are squashed up to the left of the histogram (not to the right as the workbook states. We learnt earlier that dark tones sit at the left of the histogram!)

Finally we bring the image back to it's original state by applying another curve, the opposite to the curve applied to the picture above.

The dark image (top) with curves applied to bring the tones back to the original (bottom).
We have now mimicked what the camera sensor does for us. The importance of this to us comes when we have a lot of noise in the shadow areas. See the sharp incline in the curve in the last image. With the camera making this adjustment to bring the image up to an acceptable looking picture, it would also be increasing the visibility of any noise!

* Note that all the images on this page have been converted to 8 bit to enable them to be used in this exercise!