Jack ]]>

Besides, I have a small question about Equation (4). I think there is no “h” in the numerator. Since by taking Equation (3) to Equation (2), the h will be eliminated. Hope that I didn’t miss any important details. ]]>

All the best,

Nick. ]]>

Spatial frequency can be expressed in any convenient unit: c/p, lp/ph, lp/mm, lp/um. lp/mm is just 1000 x lp/um, see the article on units. lp/mm is often used when one wants to know the absolute performance of the imaging system in a specific spot of the field of view on the sensor as captured, regardless of display size.

]]>It seems the pixel size is set as 5 um/pixel to get the answer,right?

In the previous article you give it an relative unit instead of absolute one.

And the extinction frequency should be in the unit of cycles/mm if no pixel information is given referred to some text book.

Thanks for your reply.

]]>I couldn’t get it from the equation 2.

Thanks. ]]>

Good question, the discussion above is for *photopic *conditions where stimuli have luminances of several cd/m^2 or more and cones alone rule. R.W.G. Hunt goes on to say in his excellent book Measuring Colour that “there is a gradual change from *photopic* to *scotopic* vision as the illumination level is lowered, and in this *mesopic* form of vision both cones and rods make significant contributions to the visual response”. *Scotopic* vision is instead based on a single receptor, rods, and therefore monochromatic.