Dear,

It is true that the human eye can't discriminate more than 255 grey
values, but if false colors are created our human eye can discriminate
mare than a million grey values.
More over we sometimes use more than one channel, and this is than also
best observed with some ratio-imaging combined with false colors.
Furthermore if you look at ratios you have to mention that you create
new errors if you don't use floating point notations even if more than 8
bits are available.

Greetings,

On Tue, 21 Apr 1998, Johannes Helm wrote:

> At 10.19 fm 98-04-21 -0400, Jeff Reece wrote:
> >Dear Martin:
> >
> >I think using the words "virtually never" to describe the occurence of
> >12-bit confocal S/N is certainly appropriate if the manufacturers refuse
> >to give users this option.
>
> Good afternoon.
> I should like to comment on this issue from a technological point of view.
>
> I sometimes met the attitude amongst life-scientists "The more bits-the
> better". This simple relation is, unfortunately, often wrong.
> We've studied this problem by computer simulation as related to
> quantitative CSLM measurements applying ratio-imaging dyes and published as
> a "further result" in Cell Calcium 22(4):287-298, 1997. To tell it in a
> nutshell: As long as the number of detected photons per pixel is less than
> 256, it does in principle not make any sense to have more than 8 bits
> (since an eight-bit value, i.e. a one-byte integer, defined as an unsigned
> char can max. be 255 = pow(2.0,8.0) -1 ). Also, the human eye is, as far as
> I know, on the "limit of its specification" with 256 grey-values (hence,
> b/w screens usually display grey values 0-255). If, however, the numbers of
> detected photons per pixel exceed 255, and if the detected pixel intensity
> values are converted to floats or even doubles BEFORE any further
> processing of the raw-data images is done, even an algorithm as
> noise-enhancing as the ratio-imaging algorithms does NOT depend in any
> noticeable way on whether the raw-data images have been detected digitizing
> into 8bits, 12bits, 16bits, a.s.o.
>
> Best regards,
>
> Johannes Helm
> --
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> Paul Johannes Helm
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