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Negative values in binary byte arrary viewed in Netbeans

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nellypledge

Negative values in binary byte arrary viewed in Netbeans

Hi,
I'm debugging a plugin and I see that the values of the byte array of an ImageProcessor (using both get() and getPixels()) are 0's and -1's... I think the -1's are the true values (what are 255 in the image when you mouse-over), but haven't gone to lengths to figure that out.

When I assign a value of 255 to the image during the code it behaves as it should, and I'm curious to know the reason for the -1's?

Using get() and put() works well, but when I getPixels() and edit the values in that referenced array it does appear to change, and wondered if there are subtleties between the two and if the -1's are related.

Thanks in advance for your time.
Neil

Michael Schmid

Re: Negative values in binary byte arrary viewed in Netbeans

Hi Neil,

when you access the pixels array of a ByteProcessor, you have to apply a
mask 0xff=255 to get the pixel value:
int value = pixels[x+y*width]&0xff;
That's because the ImageJ ByteProcessor assumes unsigned values 0-255 as
usual in image processing, but the Java type 'byte' is signed, with a
range -128...+127.
It's the same for a ShortProcessor, there you have to use a mask of 0xffff.

Michael
____________________________________________________________

On Thu, March 31, 2016 03:38, nellypledge wrote:

> Hi,
> I'm debugging a plugin and I see that the values of the byte array of an
> ImageProcessor (using both get() and getPixels()) are 0's and -1's... I
> think the -1's are the true values (what are 255 in the image when you
> mouse-over), but haven't gone to lengths to figure that out.
>
> When I assign a value of 255 to the image during the code it behaves as it
> should, and I'm curious to know the reason for the -1's?
>
> Using get() and put() works well, but when I getPixels() and edit the
> values
> in that referenced array it does appear to change, and wondered if there
> are
> subtleties between the two and if the -1's are related.
>
> Thanks in advance for your time.
> Neil
>
>
>
> --
> View this message in context:
> http://imagej.1557.x6.nabble.com/Negative-values-in-binary-byte-arrary-viewed-in-Netbeans-tp5016033.html
> Sent from the ImageJ mailing list archive at Nabble.com.
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>

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ImageJ mailing list: http://imagej.nih.gov/ij/list.html

nellypledge

Re: Negative values in binary byte arrary viewed in Netbeans

Thanks Michael for those crucial details.

Could I also ask if I can update the contents of the getPixels byte array reference by simply assigning values to the reference? I've always struggled with java 'pointers'.

Thanks

Neil

From: "Michael Schmid-3 [via ImageJ]" <ml-node+[hidden email]>
Sent: Mar 31, 2016 11:50 AM
To: Anthony, Neil
Subject: Re: Negative values in binary byte arrary viewed in Netbeans

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Michael Schmid

Re: Negative values in binary byte arrary viewed in Netbeans

Hi Neil,

yes, you can modify the byte values in the pixels array. This is best done
in a PlugInFilter. This will provide all the necessary infrastructure such
as preparing for Undo, checking whether it is an 8-bit image, etc.
Do the modifications in the PlugInFilter's run(ip) method.

Roughly like this (I did not try, there might be mistakes in it):

public class My_Multiply_Plugin implements PlugInFilter {
final static int flags = DOES_8G; //only for 8-bit images

public int setup(String arg, ImagePlus imp) {
return IJ.setupDialog(imp, flags); //ask in case of a stack
}

public void run(ImageProcessor ip) {
pixels = (byte[])ip.getPixels();
for (int i=0; i<pixels.length; i++) {
int value = pixels[i]&0xff;
value = value*2;
if (value > 255) value = 255;
pixels[i] = (byte)value;
}
}
}

If you want a dialog for the filter parameters and preview, use the
ExtendedPlugInFilter interface.

Michael
__________________________________________________________________

On Thu, March 31, 2016 20:10, nellypledge wrote:

> Thanks Michael for those crucial details.
>
> Could I also ask if I can update the contents of the getPixels byte array
> reference by simply assigning values to the reference? I've always
> struggled with java 'pointers'.
>
> Thanks
> Neil
>
>
> From: "Michael Schmid-3 [via ImageJ]"
> <[hidden email]>
> Sent: Mar 31, 2016 11:50 AM
> To: Anthony, Neil
> Subject: Re: Negative values in binary byte arrary viewed in Netbeans
>
> Hi Neil,
>
> when you access the pixels array of a ByteProcessor, you have to apply a
> mask 0xff=255 to get the pixel value:
> int value = pixels[x+y*width]&0xff;
> That's because the ImageJ ByteProcessor assumes unsigned values 0-255 as
> usual in image processing, but the Java type 'byte' is signed, with a
> range -128...+127.
> It's the same for a ShortProcessor, there you have to use a mask of
> 0xffff.
>
> Michael
> ____________________________________________________________
>
> On Thu, March 31, 2016 03:38, nellypledge wrote:
>
>> Hi,
>> I'm debugging a plugin and I see that the values of the byte array of an
>> ImageProcessor (using both get() and getPixels()) are 0's and -1's... I
>> think the -1's are the true values (what are 255 in the image when you
>> mouse-over), but haven't gone to lengths to figure that out.
>>
>> When I assign a value of 255 to the image during the code it behaves as
>> it
>> should, and I'm curious to know the reason for the -1's?
>>
>> Using get() and put() works well, but when I getPixels() and edit the
>> values
>> in that referenced array it does appear to change, and wondered if there
>> are
>> subtleties between the two and if the -1's are related.
>>
>> Thanks in advance for your time.
>> Neil
>>
>>
>>
>> --
>> View this message in context:
>> http://imagej.1557.x6.nabble.com/Negative-values-in-binary-byte-arrary-viewed-in-Netbeans-tp5016033.html
>> Sent from the ImageJ mailing list archive at Nabble.com.
>>
>> --
>> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>>
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>
>
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> ________________________________
>
> This e-mail message (including any attachments) is for the sole use of
> the intended recipient(s) and may contain confidential and privileged
> information. If the reader of this message is not the intended
> recipient, you are hereby notified that any dissemination, distribution
> or copying of this message (including any attachments) is strictly
> prohibited.
>
> If you have received this message in error, please contact
> the sender by reply e-mail message and destroy all copies of the
> original message (including attachments).
>
>
>
>
> --
> View this message in context:
> http://imagej.1557.x6.nabble.com/Negative-values-in-binary-byte-arrary-viewed-in-Netbeans-tp5016033p5016038.html
> Sent from the ImageJ mailing list archive at Nabble.com.
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>

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nellypledge

RE: Negative values in binary byte arrary viewed in Netbeans

Thanks Michael, that sorted it. Cooking on gas now ;)

Neil

From: Michael Schmid-3 [via ImageJ] [mailto:ml-node+[hidden email]]
Sent: Thursday, March 31, 2016 4:45 PM
To: Anthony, Neil
Subject: Re: Negative values in binary byte arrary viewed in Netbeans

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