Posted by
Antje-2 on
Mar 07, 2007; 2:09pm
URL: http://imagej.273.s1.nabble.com/Focus-measurement-more-general-image-analysis-question-tp3700123p3700135.html
Hi Gabriel,
In general you are completely right! But I don't have the possibility to
get more than one shot per scene. That's a fact!
I was hoping that there is some kind of measurement which can judge on
"sharpness" for images with different content independently from the
content. So, that I can get values which are comparable between images
with different densities of cells e.g.
Then, I can have a look at these values and decide where to put the
threshold to judge if something is in focus or not. But therefore, I
need some kind of content independent measurement...
I can assume that all images have the same kind of content (sharp scenes
of nuclei for example) and now I'd like to compare these images not
taking into account the amount of "content".
Maybe it is not possible (I don't wanna believe... )
But sooner or later I have to overcome this problem...
Antje
Gabriel Landini schrieb:
> On Wednesday 07 March 2007 13:10:27 Antje wrote:
>> But still I have a question. How shall I compare
>> images with different density? Because the standard deviation of an
>> image will be dependent on the density of objects. It may happen, that
>> there is just one cell within one image and it can also happen, that
>> there is no background at all because of the density of cells...
>
> I think it is not possible to get a robust method of sorting
> *single* images according to their degree of "in-focusness".
>
> The assumption of an absolute measure of sharpness for a single image most
> probably would not hold unless you know already what to expect in the image.
>
> If you look/google/search autofocus, you will find that all focusing
> algorithms try to maximise some measure of sharpness across several shots of
> the *same scene*.
> With a single arbitrary image (as I believe is your case), how do you make
> sure that the image is blurry because of bad focus rather than the scene
> having originally no sharp edges.
> I.e. is this 1) a blurry shot of a sharp scene or 2) is it a sharp shot of a
> diffuse-looking scene?
>
> If you look for high frequency contents in the image to make the decision, you
> would treat the 2 examples above as the same, while an autofocus algorithm
> would find the best solutions for both cases (by taking more shots at various
> focal lengths). You then could compare which one was more out of focus (how
> far away each image was from the "best focus" shot).
> But you cannot do this with a single shot of unknown properties when "in
> focus".
>
> Cheers,
> G.
>
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