Posted by
James Pawley on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Re-Ana-alarming-amount-of-image-manipulation-tp592857p1314158.html
>Johan,
>
>I have no problem with lossless compression, LZW etc. I do have a
>problem with people using "high quality" jpegs which might look the
>same, but introduce high frequency pixel level artifacts.
>Colocalization and other correlation dependent imaging methods can
>suffer. Resolution can suffer. As far as transfer rates, I am
>patient and have no problem waiting 20 min to download a gigabyte
>image file to my home office. Storage is an issue but I am of the
>opinion that it is especially important to keep at least two copies
>of the original unmanipulated data with at least one on a read only
>memory format such as a DVD. Patents (or academic reputations) can
>succeed or fail on being able to justify a claim.
>
About the travesty in Minnesota: Shame! Shame!!
About saving storage space.
It is true that noisy images have a lot of high-frequency info in
them and that efforts to compress them must necessarily introduce
some changes that may confuse later efforts at image analysis.
However, if the brightest pixel in you data represents only16
photons, you lose nothing by clipping the data to 16 levels or 4
bits. This too will speed retrieval and husband disk space.
Of you could do what NASA used to do with its images and store only
the sqrt of the intensity number (expressed in photons or
photoelectrons). This means that you only store gray levels that are
significantly different from each other, but it also takes half the
disk space (4 bits for the signal above).
In any case, assuming that you have Nyquist-sampled your data, you
should always deconvolve it before viewing it. This not only averages
out a lot of that fuzzy noise, it also allows you to meet the Nyquist
reconstruction condition: that the bandwidth of the output device
(i.e., the computer plus the LCD screen) is the same as that of the
input the device (i.e, the diffraction-limited microscope)
Hope that you are all surviving better than your hedge funds.
Jim P.
>>Mario wrote:
>>...
>>> upon request. In fact, uncompressed raw image files should be provided
>>> to the reviewers of a paper. Might save a lot time. As for Catherine
>>> Verfaillie and colleagues, without knowing the details, it seems like
>>> a black eye on common sense on the part of U of Minn. sorry don't mean
>>> to offend but consider item 2.
>>it's about time to get this straight (mario might have just a typo here,
>>not claiming anything for him):
>>
>> compression does NOT imply reduced image quality
>>
>>but it does for sure increase the speed of disk transfer, and if you
>>know what you are doing, some but not all compression algorithms can
>>*optionally* trade high frequency information (noise) for disk space.
>>avoid using the terminology that "compression" destroys images because
>>it confuses non-experts into thinking they should be storing the images
>>uncompressed. there's a factor 2-10 to gain in disk space/speed for
>>normal images.
>>
>>/Johan (who is very tired of re-teaching about compression)
>>
>>--
>>--
>>------------------------------------------------
>>Johan Henriksson
>>MSc Engineering
>>PhD student, Karolinska Institutet
>>
http://mahogny.areta.org http://www.endrov.net>
>
>--
>________________________________________________________________________________
>Mario M. Moronne, Ph.D.
>
>
[hidden email]
>
[hidden email]
>
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--
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