Posted by
Jacob Keller-2 on
URL: http://imagej.273.s1.nabble.com/Log-Math-Function-tp5020510p5020512.html
By deductive reasoning from the documentation, the answer is that "log" in
imagej means base 2. I just found out that in general:
- x = log y often means x = loge y in *mathematics* texts.
- x = log y often means x = log10 y in *science* and *engineering*
texts.
- x = log y often means x = log2 y in *computer science* texts.
This is pretty insane, almost guaranteeing we will stay in our fields and
not understand each other. I had been used to Log = base10 and ln = base e,
but never ran across the base2 parlance before. Maybe adding clarification
to the imagej documentation below would help some of us
non-computer-scientists? Here is the online documentation for the log
function, clearly-explained for computer scientists ;)
Log...
For 8-bit images, applies the function *f(p) = log(p) * 255/log(255)* to
each pixel (*p*) in the image or selection. For RGB images, this function
is applied to all three color channels. For 16-bit images, the image min
and max are used for scaling instead of 255. For float images, no scaling
is done. To calculate log10 of the image, multiply the result of this
operation by 0.4343 (1/log(10).
On Tue, Apr 17, 2018 at 3:17 PM, Gabriel Landini <
[hidden email]>
wrote:
> On Tuesday, 17 April 2018 20:08:10 BST you wrote:
> > Does anyone know what is going on with the Log function in
> > process->math->Log? I have a post-Log'd image that goes up to 302, which
> > seems rather high, esp considering that my pre-Log image maximum is 302.
> > Does it just re-scale to the original min/max or something?
> >
> > Changing to 32-bit lowers the final numbers, but the numbers are still
> off.
> > Any way to get the actual values for the logs?
>
> Please read the online documentation. It is clearly explained.
>
> Cheers
>
> Gabriel
>
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