Negative values

[sergi64]

I am opening some images to make densities and noise numbers. The problem I
have is that when I open the image (16 bits) "values" appear in negative.
For example, outside my sample (is all black) shows -1000 value.

The histogram that is showed when I make a ROI is on scale that includes
negative values.


thank you so much.




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[Herbie]

Good day,

are these CT images in DICOM format?

They may be converted to 32bit. Please check the subtitle of your images in
ImageJ, i.e. the line where the image dimensions, bit depth and file size
are listed.

What does "ImageJ >> Show Info" tell you?

Also have a look at
<https://imagej.nih.gov/ij/docs/guide/146-28.html#infobox:DisplayRangeDICOM>
although some changes were made more recently:
Search for DICOM in
<https://imagej.nih.gov/ij/notes.html>

What version of ImageJ are you using?

Regards

Herbie

:::::::::::::::::::::::::::::::::::::

I am opening some images to make densities and noise numbers. The problem I
have is that when I open the image (16 bits) "values" appear in negative.
For example, outside my sample (is all black) shows -1000 value.

The histogram that is showed when I make a ROI is on scale that includes
negative values.


thank you so much.



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[sergi64]

Images are on 16-bits. Archives: ".dcm"
I am Using FIJI 1.52n

And it is a requirement that the images do not change so I do not know if
passing them to 32 bits would be in breach of that rule.


Info on "show info":
 
Title: XXXX.dcm
Width:  200.2000 mm (1001)
Height:  200.2000 mm (1001)
Size:  1.9MB
Resolution:  5 pixels per mm
Pixel size: 0.2x0.2 mm^2
ID: -4
Bits per pixel: 16 (unsigned)
Display range: -654 - 1846
No threshold
Magnification: 0.75
ScaleToFit: false
 
Calibration function: y = a+bx
  a: -1000.000000
  b: 1.000000
  Unit: "Gray Value"
Path: C:/xxx/xxxx/xxxxxxxxxx.dcm
Screen location: 2069,156 (1920x1080)
No overlay




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[Herbie]

Your images are in DICOM-format and have been converted to 32bit (ImageJ
can't display negative integers) in order to display them according to
the DICOM metadata. I guess the images are CT-scans in Hounsfield units.
See: <https://en.wikipedia.org/wiki/Hounsfield_scale>

The "Display range: -654 - 1846" appears strange because Hounsfield
units start at about -1000 which stands for air.

I strongly recommend to consult the person who is responsible for the
image acquisition.

Regards

Herbie

:::::::::::::::::::::::::::::::::::::
Am 08.04.19 um 11:52 schrieb sergi64:

> Images are on 16-bits. Archives: ".dcm"
> I am Using FIJI 1.52n
>
> And it is a requirement that the images do not change so I do not know if
> passing them to 32 bits would be in breach of that rule.
>
>
> Info on "show info":
>  
> Title: XXXX.dcm
> Width:  200.2000 mm (1001)
> Height:  200.2000 mm (1001)
> Size:  1.9MB
> Resolution:  5 pixels per mm
> Pixel size: 0.2x0.2 mm^2
> ID: -4
> Bits per pixel: 16 (unsigned)
> Display range: -654 - 1846
> No threshold
> Magnification: 0.75
> ScaleToFit: false
>  
> Calibration function: y = a+bx
>    a: -1000.000000
>    b: 1.000000
>    Unit: "Gray Value"
> Path: C:/xxx/xxxx/xxxxxxxxxx.dcm
> Screen location: 2069,156 (1920x1080)
> No overlay
>
>
>
>
> --
> Sent from: http://imagej.1557.x6.nabble.com/
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>

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[Herbie]

Sorry I've misinterpreted the "Display range: -654 - 1846" which means
-654 to +1845 Hounsfield units and which is *perfectly OK*.

I think you can work with such images when imported to ImageJ!

Just keep in mind that the gray-values are scaled in Hounsfield units.

Good luck (and sorry for the confusion)

Herbie

::::::::::::::::::::::::::::::::::::
Am 08.04.19 um 11:52 schrieb sergi64:

> Images are on 16-bits. Archives: ".dcm"
> I am Using FIJI 1.52n
>
> And it is a requirement that the images do not change so I do not know if
> passing them to 32 bits would be in breach of that rule.
>
>
> Info on "show info":
>  
> Title: XXXX.dcm
> Width:  200.2000 mm (1001)
> Height:  200.2000 mm (1001)
> Size:  1.9MB
> Resolution:  5 pixels per mm
> Pixel size: 0.2x0.2 mm^2
> ID: -4
> Bits per pixel: 16 (unsigned)
> Display range: -654 - 1846
> No threshold
> Magnification: 0.75
> ScaleToFit: false
>  
> Calibration function: y = a+bx
>    a: -1000.000000
>    b: 1.000000
>    Unit: "Gray Value"
> Path: C:/xxx/xxxx/xxxxxxxxxx.dcm
> Screen location: 2069,156 (1920x1080)
> No overlay
>
>
>
>
> --
> Sent from: http://imagej.1557.x6.nabble.com/
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>

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