[obican]

Btw, I suggest this book to everyone, Post Exposure: Advanced Techniques for the Photographer by Ctein. Originally published in 1997, it still contains a ton of very useful information that you can benefit from in digital photography applications and online discussions. He has the entire book online at his website but it says NOT to redistribute the file, so I'm not going to.

 

 

To have some quotes from the first chapter:

 

 

 

I’ll spare you the math, which is beyond the scope of this book (it involves Fourier transforms, if you want to work it out for yourself ). The difference between a sharp edge and a fuzzy one (a square wave and a sine wave) corresponds to a difference in spatial detail three times finer than the line spacing. In other words, the resolution difference between 10 lp/mm of sharp edges and fuzzy ones is way down around 30 lp/mm. When we notice a difference between those blurry and sharp 10 lp/mm lines, we are responding to detail at 30 lp/mm, even though we can’t directly see it. That’s why materials such as dye transfer and Ektaflex, which display about 20 lp/mm, look fuzzier than chromogenic prints with over 60 lp/ mm. In a side-by-side comparison, you won’t see any more fine detail in a chromogenic print, but you will perceive the detail you can see as sharper

 

 

Our eyes distinguish a surprisingly small number of tonal steps—fewer than many films and digital sensors can. We don’t notice this because our perceptual systems work to produce an illusion of continuity. We aren’t aware of the steps in our gray response any more than we notice the “blind spot” in our retinas under normal circumstances.

 

 

“Perfect” tonality for the average viewer requires only about 650 gray steps. You can always put more squares into the tonal scale. For example, you can put that 1.01 lambert square back between the 1.00 and 1.02 squares, but you won’t be able to see it as a distinct square; it will blend perfectly into the squares on either side. No matter what you do to the gray scale, the average human will never see more than 650 squares. Visual artists frequently have better eyes than the average person, but the number of steps is still well under 1000.