Newsgroups: sci.image.processing
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From: pc22@midway.uchicago.edu (Paul Chang)
Subject: Gaussian blur=cycles/degree?
Message-ID: <pc22-1001951355210001@kbg1.spc.uchicago.edu>
Sender: news@uchinews.uchicago.edu (News System)
Organization: University of Chicago
Date: Tue, 10 Jan 1995 19:55:21 GMT
Lines: 39

Hi everyone,

I have a question about Photoshop (V.2.5 or 3.0) as someone who uses
digitized images for psychology experiments. I use retouched photos of
faces for experiments in the hemispheric specialization of face
recognition, and would like to do some experiments on the recognition of
_blurred_ faces.

I can use Gaussian Blur and the High Pass filter. For example, I can blur
an image using the Gaussian blur command in which I manipulate pixel
sharpness. However, even though I have blurred the picture, is there any
way of telling by <how much> have I blurred the photo? That is, in typical
studies where we filter images, we talk about blurring in terms of the
number of spatial frequencies, or cycles per degree.

The same problem holds for the High Pass filter. Once I have High-pass
filtered an image by putting in Photoshops arbitrary value (0.1 to 100),
what exactly does this mean with respect to say, a certain spatial
frequency cutoff for my filter? Is there any way of equating the blurring
done by Photoshop in terms of the scientifically accepted cycles per
degree measure? Does blurring by "X" percentage equal blurring by "Y"
cycles per degree? Or can we say that blurring by "X" percentage equals
high or low pass filtering done in the real world?

I have asked the tech support line at Adobe about this, but they weren't
able to give me a decent answer. If anyone has any thoughts about this, or
any references to share, I'd be grateful if you let me know. Please e-mail
me directly (preferred), or post a reply here. My address is
pc22@midway.uchicago.edu

Thanks everyone for your attention. 

Cheers, Paul.

Paul Chang
c/-Department of Psychology
University of Chicago
5848 S. University Ave
Chicago, IL 60637
