Gamma Question

[tomservo]

Hi,

I liked your Gamma presentation comparing human perception to sensor detection. From the chart, it looks as though the human eye perceives 18% actual luminance value as 50% and 50% actual luminance at 75%, while a video sensor detects 50% actual luminance as 50%. I thought the eye had a non-linear response to light values, seeing doubling of intensity as a linear increase, however the the graph shows the opposite: The eye gamma seems exaggerated, so that actual luminance is seen by the eye as disproportionally brighter values than those detected by the sensor.

I'm not interpreting this graph correctly. Any clarification would be most appreciated.

Thanks

Tom

[dje]

Hi Tom and welcome to CiC.

I'm certainly no expert on this topic but I think there is a need to recognize that the eye is more sensitive to contrast within a scene rather than absolute light intensity. The eye adjusts itself in a complex way to deal with the absolute light intensity (pupil diameter being one important factor) and I think your assumption which I quote below may be an over-simplification.

I thought the eye had a non-linear response to light values, seeing doubling of intensity as a linear increase

The discussion on non-linear gamma you refer to is dealing with contrast variation within a scene. I think you are interpreting that graph correctly.

Others may be able to provide a better explanation and in order to further that aim, I'd suggest you PM a mod and ask for your thread to be moved to a more appropriate area in the forum (where it will be more likely to be seen). eg General Photography Discussion

Dave

[IzzieK]

Tom...welcome to CiC. Please fill in your profile before someone else reminds you to do so.