Digital Images / sRGB:
link: sRGB Wikipedia.org
sRGB is designed to match what current monitors see. This standard was developed by Hewlett-Packard and MicroSoft, and has been endorsed by Intel, Pantone, Corel, to name a few. sRGB closely matches the human eye's ability to perceive luminance.
Linear and sRGB encoded grad:
Notice the linear encoded grad does not look "linear" (the grey values steping evenly from black to white), while the sRGB encoded grad looks smooth (linear). Also notice the position of the "mid grey point", this is the opposite of what you would expect in each of the encoded grads.
The reason for this is because Nuke is applying a LUT (look up table) to the image.
This can be adjusted by hitting the "s" key in nuke, selecting the LUT tab, and adjust the Default LUT settings as needed. (see image below).
A Linear LUT would look similar the curve to the left.
The Black Point would be on the lower left at 0.0.
The Mid Grey Point would be at 0.5.
The White Point would be at 1.0 on the upper right of the graph.
* 0.5 is the midpoint of the image data.
sRGB allows you to store more data in the darker end of the color spectrum, where the human eye is more sensitive. If you look at the curve on the left you will notice that most of the curve is below the 0.5 level, telling us that most of the data is stored there.
This allows us to store more detail in the shadows and have less banding and other unwanted artifacts.
The sRGB LUT: basically the opposite of it's sRGB counterpart.
This curve with will "linearize" what you see in the Nuke viewer.
Linear grad with linear encoding, the mid grey point is at the halfway point of the grad.
The mid grey point (center point) of the sRGB image is at about 75% mark of the grad.
Again: sRGB stores much more detail in the darker end of the color spectrum.
(see image below).