Re: how to mark single pixel in a overlay

Posted by Robert Baer on Jan 09, 2016; 12:56am
URL: http://imagej.273.s1.nabble.com/how-to-mark-single-pixel-in-a-overlay-tp5015334p5015354.html

On 1/8/2016 1:05 PM, Kenneth Sloan wrote:
> Absolutely NOT.  A pixel is an *area*, not a *point*.
>
> Where this area is wrt an x,y coordinate is a matter of *convention*, not *taste*
>
> The first order of business for any image processing system is to establish and enforce that convention.

This discussion compels me to share the link to this classic paper by
Alvy Ray Smith that I learned about from this list many years ago.  If
you have never read it, you are probably in for a treat. The title is,
/*"A Pixel is not a little square, A Pixel is not a little square, A
Pixel is not a little square, (and a voxel is not a little cube)"*/

You can find it here http://alvyray.com/Memos/CG/Microsoft/6_pixel.pdf

Enjoy,
Rob

>
> --
> Kenneth Sloan
> [hidden email]
> Vision is the art of seeing what is invisible to others.
>
>
>
>
>> On Jan 7, 2016, at 08:30 , Herbie <[hidden email]> wrote:
>>
>> Dear Jeremy,
>>
>> let's face it: A pixel has no extension, it is a (point with an associated) number.
>>
>> What you call a pixel, is part of a zero-order interpolation of an array of points (numbers), i.e. an area of equal gray-level or colour.
>>
>> How this area is positioned with respect to the underlying number is a matter of taste. The area may be centered to the number or the number may be on its upper left corner.
>>
>> Guess what is the case when displaying images in ImageJ...
>>
>> I know, all this won't help with your problem, but perhaps it makes the issue clearer.
>>
>> Best
>>
>> Herbie
>>
>> ::::::::::::::::::::::::::::::::::::::::::
>> Am 07.01.16 um 13:45 schrieb Jeremy Adler:
>>> I am want to use the overlay to mark a single pixel in an image that
>>> has been zoomed to show individual pixels - within a macro.
>>>
>>> But I cannot see how to mark a single pixel in the overlay.
>>> Overlay.drawRect   marks an area of 2x2 pixels centred on my target
>>> pixel but 1x1 Overlay.drawLine  with the two positions set the same,
>>> marks a single pixel offset
>>>
>>> I can mark a single pixel using the ROI manager and then move it and
>>> convert it to an overlay, but this seems unduly cumbersome, is there
>>> a better way of marking single pixels in a overlay ?
>>>
>>>
>>> Dr Jeremy Adler Senior res engineer BioVis Dag Hammarskjölds väg 20
>>> Uppsala Universitet,  752 37 Uppsala ,Sweden
>>>
>>>
>>>
>>> [phone]
>>>
>>> http://www.biovis.uu.se
>>>
>>>
>>>
>>>
>>> -- ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>>>
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