RV: Question for 8-bit grayscale values

[pvizan]

Dear all, we have a question for quantification methods of ImageJ, could
anybody help us?

 

For an optical density calibration, when you are capturing 8-bit grayscale
images (values from 0-256), it is supposed that the darkest standard picture
corresponds to the lowest value. In our case that is not true, the darkest
standard picture is shown as the clearest picture and the mean value is the
highest. It seems that the camera is acquiring the picture in “negative
mode”. Does it make any sense? Does anybody know how to change/solve it?

 

Thank you very much in advance

 

Pedro

 

--

 

Pedro Vizán, PhD.

Departament of Biochemistry and Molecular Biology

Institute of Biomedicine of University of Barcelona

phone number: 0034 934021217

e-mail: [hidden email]

 

[Adrian Daerr-2]

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> For an optical density calibration, when you are capturing 8-bit grayscale
> images (values from 0-256), it is supposed that the darkest standard picture
> corresponds to the lowest value. In our case that is not true, the darkest
> standard picture is shown as the clearest picture and the mean value is the
> highest. It seems that the camera is acquiring the picture in “negative
> mode”. Does it make any sense? Does anybody know how to change/solve it?

Both conventions exist (the black=0/white=255 convention is the most
common for video acquisition because a pixel integrates light, and so
its value corresponds to the intensity; the black=255/white=0 convention
is more common in printing, because here people are used to indicating
the amount of toner when printing on white paper). Likely your
acquisition hardware/software follows a different convention from ImageJ
(ImageJ's predecessor NIHImage had the opposite convention, if I recall
correctly...).

Simple solution: just invert your movie after acquisition
(Edit->Invert). Otherwise find out how to modify the acquisition process...

best regards,
Adrian

- --
http://www.msc.univ-paris-diderot.fr/~daerr/
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[pvizan]

Dear all,


For an optical density calibration, when you are capturing 8-bit grayscale
images (values from 0-256), it is supposed that the darkest standard picture
corresponds to the lowest value (black=0/white=255 convention), but in our
case we have a black=255/white=0 convention. Does anybody know how to modify
the acquisition process to invert the O.D. values? Using "Edit -> Invert"
does not change O.D. values.

Pedro

PS: We are using a Leica DM4000B digital microscopy. For image capturing a
monochrome digital camera Scion CFW-1312M is being used.

--

Pedro Vizán, PhD.
Departament of Biochemistry and Molecular Biology
Institute of Biomedicine of University of Barcelona
phone number: 0034 934021217
e-mail: [hidden email]
 

[Joachim Wesner]

ImageJ Interest Group <[hidden email]> schrieb am 27.03.2008 17:03:11:

> Dear all,
>
>
> For an optical density calibration, when you are capturing 8-bit
grayscale
> images (values from 0-256), it is supposed that the darkest standard
picture
> corresponds to the lowest value (black=0/white=255 convention), but in
our
> case we have a black=255/white=0 convention. Does anybody know how to
modify
> the acquisition process to invert the O.D. values? Using "Edit -> Invert"
> does not change O.D. values.
>
> Pedro
>

Pedro,

easy, you should be able to use "Process/Math/XOR" with 255

Joachim


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