http://imagej.273.s1.nabble.com/How-is-the-line-plot-profile-generated-tp5015838p5015872.html
> Hi Herbie,
>
> Thanks for your reply.
>
> as Avital might have told you, the line profile uses nearest neighborhood
>> interpolation and I assume that coordinates having xy.5 values will be
>> rounded up.
>>
>>
> The line profile uses continuous coordinates and there is no rounding as
> far as I can see. That's perhaps clearer if you use the "live" mode of the
> profile plot and move a line around.
>
>
>> Please note that pixel values are mathematical points and the squares that
>> are commonly mistaken as pixels are for visualization only.
>>
>
> I see what you mean but I don't fully agree because (i) camera sensors are
> not dimensionless, they take up space and I find pixels a convenient
> physical representation of sensors, beyond just being a "data structure".
> And (ii) light captured by cameras is not discreet but continuous, and one
> can try to estimate continuous parameters from pixel data. i.e., sub-pixel
> information can be inferred from the data.
>
> All the best,
>
> Emmanuel
>
>
>
>
>> HTH
>>
>> Herbie
>>
>> :::::::::::::::::::::::::::::::::::::::::::
>> Am 13.03.16 um 20:50 schrieb Emmanuel Levy:
>>
>>> Dear All,
>>>
>>> I wished to add a piece of macro to illustrate the behaviour I observed
>>> and
>>> was describing (see below).
>>>
>>> Discussing offline with Avital made it clear what happens: pixel values
>>> are
>>> represented by the image-coordinate system and this introduces asymmetry -
>>> let's consider 3 pixels:
>>> - x=0,y=0 (black)
>>> - x=0,y=1 (white)
>>> -x=0,y=2 (black)
>>>
>>> If I draw two horizontal lines at y=0.5 and y=2.5. They are both
>>> equidistant from the white pixel on the image (i.e., it looks symmetric)
>>> but they are not equidistant in the coordinate system, the line at y=0.5
>>> is
>>> only 0.5 pixels far from the while pixel's origin (at x=0,y=1), while the
>>> line at y=2.5 is 1.5 pixels away. This introduces asymmetry when plot
>>> profile calculates values.
>>>
>>> Would anyone know of a way of producing a symmetric behaviour for plot
>>> profile?
>>>
>>> Thanks for your help,
>>> All the best,
>>>
>>> Emmanuel
>>>
>>>
>>> ===========
>>>
>>> The macro below creates a whitish region at the centre of a 17 by 17px
>>> image, and adds a white pixel at the top of the image as well. It then
>>> draws two pairs of lines. I would expect the profile for the two pairs to
>>> be identical because the pixel environment is identical. However, the two
>>> profiles within each pair are different. e.g., if the line is 0.5 pixel
>>> above or below a white pixel will yield a very different outcome.
>>>
>>> newImage("Untitled", "8-bit Black", 17, 17, 1);
>>> makeRectangle(8, 8, 1, 1);
>>> run("Clear", "slice");
>>> run("Select All");
>>> run("Gaussian Blur...", "sigma=2");
>>> makeRectangle(7, 1, 1, 1);
>>> run("Clear", "slice");
>>> run("Enhance Contrast", "saturated=0.35");
>>>
>>> ///// FIRST PAIR OF PROFILES (left and right to the whitish spot)
>>> selectWindow("Untitled");
>>> makeLine(4.5, 5.5, 4.5, 11.5);
>>> run("Plot Profile");
>>>
>>> selectWindow("Untitled");
>>> makeLine(12.5, 5.5, 12.5, 11.5);
>>> run("Plot Profile");
>>>
>>>
>>> ///// SECOND PAIR OF PROFILES (top and bottom to the white pixel)
>>> selectWindow("Untitled");
>>> makeLine(5.5, 0.5, 9.5, 0.5);
>>> run("Plot Profile");
>>>
>>> selectWindow("Untitled");
>>> makeLine(5.5, 2.5, 9.5, 2.5);
>>> run("Plot Profile");
>>>
>>> On 10 March 2016 at 10:06, Jan Eglinger <
[hidden email]> wrote:
>>>
>>> Dear Avital and Emmanuel,
>>>>
>>>> On 9 March 2016 at 21:28, Avital Steinberg <
[hidden email]>
>>>>> wrote:
>>>>>
>>>>>> Herbie helped me in the other ImageJ forum
>>>>>>
>>>>>
>>>> Let's be nice and link to this discussion, so others can follow:
>>>>
http://forum.imagej.net/t/how-is-the-plot-profile-calculated/1070>>>>
>>>>
>>>> On 10.03.2016 07:26, Emmanuel Levy wrote:
>>>>
>>>> I would have expected that, by default, only the pixels onto which the
>>>>> line
>>>>> is drawn are used and interpolated when calculating the profile. Is this
>>>>> non-symmetric behaviour of the interpolation an intended behaviour?
>>>>>
>>>>>
>>>> I agree that there are inconsistencies between how lines and segmented
>>>> line selection are displayed on the image and the measurements of those
>>>> lines. Please see also my following related post on the forum:
>>>>
>>>>
>>>>
>>>>
http://forum.imagej.net/t/change-in-pixels-using-reslice-function/999/2?u=imagejan>>>>
>>>>
>>>> I remember previous discussions about rectangular selections and the
>>>> behavior of the Fill and Draw commands that by now have been fixed. It
>>>> would be great to have a consistent ROI behavior through all types of
>>>> selections in ImageJ.
>>>>
>>>> Cheers,
>>>> Jan
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>> On 9 March 2016 at 21:28, Avital Steinberg <
[hidden email]>
>>>>> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>>> When I use ImageJ's graphical user interface and draw a line and then
>>>>>> select Analyze, plot profile (with the default settings), I get a plot
>>>>>> of
>>>>>> intensities vs. the distance from the beginning of the line. I was
>>>>>> wondering how the plot is generated, in terms of which pixels in the
>>>>>> neighborhood are taken into the weighted average, and how the weights
>>>>>> are
>>>>>> determined.
>>>>>>
>>>>>> Herbie helped me in the other ImageJ forum by suggesting that I plot a
>>>>>> ramp
>>>>>> image. Now I can sometimes predict the values that will appear in the
>>>>>> profile plot. (but only in some simple cases) After experimenting with
>>>>>> an
>>>>>> image, I noticed that the plot's x-axis scale changes abruptly from 1.5
>>>>>> to
>>>>>> 2.0 (for example) and I was wondering if the distance between 2
>>>>>> adjacent
>>>>>> points changes when the scale suddenly changes.
>>>>>>
>>>>>> Thank you,
>>>>>> Avital
>>>>>>
>>>>>>
>>>>>
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http://imagej.nih.gov/ij/list.html>>>
>>>
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