Re: automatic detection out-of-focus images

Posted by Gabriel Landini on Mar 14, 2011; 5:05pm
URL: http://imagej.273.s1.nabble.com/JACoP-parameter-and-PSF-tp3685080p3685089.html

On Monday 14 Mar 2011 15:49:25  Baron, Ken (US SSA) wrote:
> Just compress your images with jpeg or probably any image compressor. The
> file that is the largest is probably the one with best focus.

That would only work if all the images were of the same scene which is not the
case here.  A "busy" image out of focus may well take more space to store
compressed than one with very few objects but well in focus.
This would not work either when parts of the image are in focus and others are
not.
Rather than compressing the image, it would be better to look at the high
frequencies (for example in the Fourier space), but even so, this makes sense
only when you compare images of the same (or very similar) scene. This would
fail when the image is originally lacking high frequency components.

Anyway, finding the best focused image requires looking how much focus can be
achieved at other focal distances. The eye does it and photo cameras do it
that way too.
Have a look at various papers on autofocus techniques (which search for the
best focused image) to get an idea how these things are implemented.
Understanding the technical problem might help realising what can and cannot
be achieved under certain constraints.

Roca X, Binefa X, Vitria J. New autofocusing algorithm for cytological tissue
in a microscopy environment. Optical Engineering 1998;37(2):635-641.

Firestone L, Cook K, Culp K, Talsania N, Preston K. Comparison of autofocus
methods for automated microscopy. Cytometry 1991;12:195-206.

Santos A, Ortiz de Solorzano C, Vaquero JJ, Pena JM, Malpica N, Del Pozo F.
Evaluation of autofocus functions in molecular cytogenetic analysis. Journal
of Microscopy 1997;188(3):264-272.

Pieper RJ, Korpel A. Image processing for extended depth of field. Applied
Optics 1983;22(10):1449-1453.

I hope this is useful.
Regards

Gabriel