Save as PNG problem

[Roger Bourne]

Dear List

My students have found some apparently inconsistent behavior with the
Save As PNG command.
We opened a 16 bit dicom and used Menu: Image > Type to change to 8 bit
before saving as PNG.  Also saved as 16 bit PNG prior to this.
The PNG file size was the same in both cases.

Similarly, when an 8 bit PNG was opened and changed to 16 bit before
saving as PNG there was no change in file size and the reopened file
appears to still be 8 bit.

Conclusion: It appears that the Save As PNG command is not reading the
currently set bit depth.

IJ 1.41o  Java 1.6.0_10

Thanks
Roger

--
-----------------------------------
Dr Roger Bourne
Lecturer, Medical Radiation Physics
Medical Radiation Sciences
University of Sydney
Tel: [phone]
Fax: [phone]

C42 - Cumberland Campus
The University of Sydney
East Street
Lidcombe
NSW 2141 Australia
-----------------------------------

[Wayne Rasband]

On Aug 10, 2009, at 12:25 AM, Roger Bourne wrote:

> Dear List
>
> My students have found some apparently inconsistent behavior with the
> Save As PNG command.
> We opened a 16 bit dicom and used Menu: Image > Type to change to 8
> bit before saving as PNG.  Also saved as 16 bit PNG prior to this.
> The PNG file size was the same in both cases.
>
> Similarly, when an 8 bit PNG was opened and changed to 16 bit before
> saving as PNG there was no change in file size and the reopened file
> appears to still be 8 bit.
>
> Conclusion: It appears that the Save As PNG command is not reading the
> currently set bit depth.

The File>Save As>PNG command saves 16-bit images as 8-bit PNGs. It does
this so that the images are displayed corruptly in PNG readers such as
Photoshop that expect 16-bit PNGs to use the full 0-65535 (or 0-32767)
pixel value range.

-wayne

[Harry Parker]

Hi Roger,

If you need to save 16 bit PNG files, you can use the Image IO plugins set found at
http://ij-plugins.sourceforge.net/plugins/imageio/index.html.

Then look for the 2nd PNG..., below the line in the Save As... submenu.

 --
Harry Parker
Senior Imaging Systems Engineer







________________________________
From: Roger Bourne <[hidden email]>
To: [hidden email]
Sent: Monday, August 10, 2009 12:25:41 AM
Subject: Save as PNG problem

Dear List

My students have found some apparently inconsistent behavior with the Save As PNG command.
We opened a 16 bit dicom and used Menu: Image > Type to change to 8 bit before saving as PNG.  Also saved as 16 bit PNG prior to this.
The PNG file size was the same in both cases.

Similarly, when an 8 bit PNG was opened and changed to 16 bit before saving as PNG there was no change in file size and the reopened file appears to still be 8 bit.

Conclusion: It appears that the Save As PNG command is not reading the currently set bit depth.

IJ 1.41o  Java 1.6.0_10

Thanks
Roger

-- -----------------------------------
Dr Roger Bourne
Lecturer, Medical Radiation Physics
Medical Radiation Sciences
University of Sydney
Tel: [phone]
Fax: [phone]

C42 - Cumberland Campus
The University of Sydney
East Street
Lidcombe
NSW 2141 Australia
-----------------------------------