Conversion to 32-bit resets the contrast range

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Conversion to 32-bit resets the contrast range

Stein Rørvik
Here is another issue related to min/max values:

If you convert an 8-bit or 16-bit image to 32-bit, the contrast range is changed, so that the current min/max values are lost.

In the below demo macro we see that the T1 Head image (which is not density calibrated)
is reset to a min,max range of 0,230 which seems to be a bit arbitrary.

The CT image (which is density calibrated) is reset to the min/max values of the image.

I see no reason not to preserve the min/max values in these cases, as the dynamic range of the image is always preserved when converting to higher bit depths.

------------------------------
print("\\Clear");

run("T1 Head (2.4M, 16-bits)");
setSlice(nSlices/2);
getMinAndMax(min, max);
print(min, max);
run("32-bit");
getMinAndMax(min, max);
print(min, max);

run("CT (420K, 16-bit DICOM)");
getMinAndMax(min, max);
print(min, max);
run("32-bit");
getMinAndMax(min, max);
print(min, max);
------------------------------

I am using daily build ImageJ 1.52k with Java 1.6 on Windows 7/64-bit.


Stein


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Re: Conversion to 32-bit resets the contrast range

Cammer, Michael-2
For macros I often find it is useful to keep the contrast scaling and channel colors in variables (usually an array of # channels) to reapply after processing or remerging.
Cheers-
Michael C

-----Original Message-----
From: Stein Rørvik <[hidden email]>
Sent: Friday, January 11, 2019 5:41 AM
To: [hidden email]
Subject: Conversion to 32-bit resets the contrast range

Here is another issue related to min/max values:

If you convert an 8-bit or 16-bit image to 32-bit, the contrast range is changed, so that the current min/max values are lost.

In the below demo macro we see that the T1 Head image (which is not density calibrated) is reset to a min,max range of 0,230 which seems to be a bit arbitrary.

The CT image (which is density calibrated) is reset to the min/max values of the image.

I see no reason not to preserve the min/max values in these cases, as the dynamic range of the image is always preserved when converting to higher bit depths.

------------------------------
print("\\Clear");

run("T1 Head (2.4M, 16-bits)");
setSlice(nSlices/2);
getMinAndMax(min, max);
print(min, max);
run("32-bit");
getMinAndMax(min, max);
print(min, max);

run("CT (420K, 16-bit DICOM)");
getMinAndMax(min, max);
print(min, max);
run("32-bit");
getMinAndMax(min, max);
print(min, max);
------------------------------

I am using daily build ImageJ 1.52k with Java 1.6 on Windows 7/64-bit.


Stein


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Re: Conversion to 32-bit resets the contrast range

Wayne Rasband-2
In reply to this post by Stein Rørvik
> On Jan 11, 2019, at 5:40 AM, Stein Rørvik <[hidden email]> wrote:
>
> Here is another issue related to min/max values:
>
> If you convert an 8-bit or 16-bit image to 32-bit, the contrast range is changed, so that the current min/max values are lost.

This bug is fixed in the latest ImageJ daily build (1.52k17).

-wayne

> In the below demo macro we see that the T1 Head image (which is not density calibrated)
> is reset to a min,max range of 0,230 which seems to be a bit arbitrary.
>
> The CT image (which is density calibrated) is reset to the min/max values of the image.
>
> I see no reason not to preserve the min/max values in these cases, as the dynamic range of the image is always preserved when converting to higher bit depths.
>
> ------------------------------
> print("\\Clear");
>
> run("T1 Head (2.4M, 16-bits)");
> setSlice(nSlices/2);
> getMinAndMax(min, max);
> print(min, max);
> run("32-bit");
> getMinAndMax(min, max);
> print(min, max);
>
> run("CT (420K, 16-bit DICOM)");
> getMinAndMax(min, max);
> print(min, max);
> run("32-bit");
> getMinAndMax(min, max);
> print(min, max);
> ------------------------------
>
> I am using daily build ImageJ 1.52k with Java 1.6 on Windows 7/64-bit.

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