[opendtv] Re: Mediaflo Technology - Mark_Schubins_Contrast_Sensitivity_Function_Presentation
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 12 Nov 2006 01:13:08 -0500
Thanks Mark -
The updated presentation is now at the same url:
<www.trbarry.com/Mark_Schubins_Contrast_Sensitivity_Function_Presentation.ppt>
- Tom
Mark Schubin wrote:
Tom Barry wrote:
For anybody still following this thread, Mark's Powerpoint
presentation can now be found on my web page at:
<www.trbarry.com/Mark_Schubins_Contrast_Sensitivity_Function_Presentation.ppt>
Here's a description of the slides:
1 - This is a contrast-resolution grating as it is normally presented,
with resolution increasing to the right and contrast decreasing to the
top. You will probably see some sort of downward-shaped curve at the
top of the grating. There is no such curve in the image. The curve is
being introduced by your visual system. The exact shape and position of
the curve will depend on your display, your distance from it, and, of
course, your visual system.
2 - This simply inverts the grating so I cam label it properly.
Resolution still increases to the right, but now contrast increases to
the top instead of to the bottom.
3 - I have drawn in a contrast-sensitivity function. Whether it matches
what you see will, again, depend on your display, your distance from it,
and your visual system. But, wherever the curve lies, everything under
it will be invisible to an observer with that contrast-sensitivity
function.
4 - This is a typical modulation-transfer-function curve shape, but how
broad the shoulder is will depend on the listed factors. The
psychological sensation of "sharpness" is proportional to the square of
the area under the curve.
5 - These are real-world MTF curves, as measured by Bob Atkins, who gave
permission to include these. They are for the two Canon still cameras
shown, with the same lens. There is a 14% linear difference in the
number of photosensors in the two cameras. Even that small increase has
made a significant increase in the sharpness. I'll send Tom another
slide that shows that sharpness increase.
New 6 (not there yet, until I send it to Tom) - A visual representation
of the sharpness difference of the two Canon cameras, based on a portion
of an image of the Canon brochure,
Old 6 (new 7, when I send Tom the sharpness illustration) - This is the
scary one. I've superimposed the hypothetical MTF curve over the
contrast-resolution grating and the CSF curve. The two particular curve
shapes and locations are hypothetical, but the fact that the wedge to
the left is all that is available and visible is not.
New 8 - I've also added this slide with two composite photographs from
Aude Oliva at MIT and Philippe Schyns at the University of Glasgow.
Again, they are used with permission. You may read a paper about those
images here:
http://cvcl.mit.edu/Papers/Schyns-Oliva99.pdf
You will probably see an angry man on the left and a neutral woman
on the right in the top, larger images. In the lower ones, you will
probably see a neutral woman on the left and an angry man on the right.
There is no difference between the upper and lower images other than
scaling. You may convince yourself of this by looking at only the top
images and walking backwards from your display until they swap.
There is a low-spatial-frequency image of a neutral woman on the
left and an angry man on the right combined with a
higher-spatial-frequency image of an angry man on the left and a neutral
woman on the right. As you walk back from your display, the peak of
your contrast-sensitivity function moves from the higher-resolution
angry man on the left to the lower-resolution neutral woman on the
left. The low-spatial-frequency information is eight cycles per facial
image; the high is 24 (equivalent to 48 pixels across). The source
images are 256 x 256 at eight bits.
Please do not re-use any of the images without permission. I will be
happy to provide contact information to you.
TTFN,
Mark
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--
Tom Barry trbarry@xxxxxxxxxxx
Find my resume and video filters at www.trbarry.com
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