Re: grayscale displays and human vision

Posted by dscho on Jul 10, 2006; 5:11pm
URL: http://imagej.273.s1.nabble.com/grayscale-displays-and-human-vision-tp3702214p3702225.html

Hi,

On Mon, 10 Jul 2006, John T. Sharp wrote:

> I'm not an authority on human vision but I read somewhere that the human
> eye could distingusih approximately 16 different gray levels. This is
> far less than 256 of 8 bit. In fact it is only 3 bit.
>
> I tested this in a small demonstration with a group of colleagues who
> spend a lot of time reading x-ray films of the hands and feet and 16
> levels appeared to be about what the best could do.

That is not a fair test. Humans are really bad at estimating _absolute_
values, especially when there is a high variation in colour, but they are
wonderful with _relative_ values, especially when there is next to no
variation. Try this macro:

-- snip --
r1=192; r2=197;
w=400; h=400;
newImage("Cascade", "RGB White", w, h, 1);
makeRectangle(0, 0, w/2, h);
setForegroundColor(r1, r1, r1);
run("Fill");
makeRectangle(w/2, 0, w, h);
setForegroundColor(r2, r2, r2);
run("Fill");
run("Select None");
-- snap --

Depending on the monitor, and your eye sight, you can make the distance
between r1 and r2 even smaller. A colleague of mine could easily discern
192 from 194.

Ciao,
Dscho