Re: grayscale displays and human vision

Posted by Jerome Mutterer on Jul 10, 2006; 5:52pm
URL: http://imagej.273.s1.nabble.com/grayscale-displays-and-human-vision-tp3702214p3702215.html

Dear all,
following this thread, I just wrote a macro Tool that might help  
exploring images with a high dynamic range. It will adjust the display  
range to the local minimum and maximum. You can try it with the CT  
example image. It can help finding details in low contrast regions.

http://rsb.info.nih.gov/ij/macros/tools/HDRexplorerTool.txt

Jerome

Quoting Johannes Schindelin <[hidden email]>:

> 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
>