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  #11  
Old August 15th 12, 06:43 PM posted to rec.photo.digital
Jeff
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Posts: 48
Default Identical Pix

"Dudley Hanks" wrote in
:


"PeterN" wrote in message
...
On 8/14/2012 6:10 PM, Dudley Hanks wrote:
"PeterN" wrote in message
...
On 8/14/2012 5:36 PM, Dudley Hanks wrote:
I had this great idea to write a Perl script to help isolate my
subjects
from their backgrounds...

I thought I could take two pics, one without the subject and one
with, both
shot in manual mode with the same settings, shot only moments apart.

Then, I thought I could run through the pixels and change the pixels
that
were the same for a different background colour, leaving the subject
intact,
as it would have pixels different from the first image.

I assumed that the pixels should be the same in the background but
different
where the subject was situated.

Interestingly, even though there is no apparent difference when
viewed side
by side, individual RGB values can vary by more than +/-25 per red,
green
or
blue component on virtually every pixel.

In spite of shooting in RAW and using lossless png source files, all
but
a
couple of hundred thousand pixels were unique between images.

I've only conducted the experiment after using Irfanview to convert
the RAW
files to png, so it could be something in this particular
application. I'll
check it out a bit more thoroughly, tomorrow, using Adobe, but it
looks as
though each shot is truly unique, regardless of how similar they
might appear.

BTW, as a control, I compared two copies of the same file, and as
one would
expect, the whole image went black, so it would seem that the script
is working properly, it's just that the rgb values are unique when
pics are
shot moments apart.

Anyone out there have any experience with trying this technique, but
with
more success?

Take Care,
Dudley

I know this doesn't answer your question, but can you put a tolerance
factor in your script.


--
Peter

Yes, it's possible, but clumsy.

First, I want to try Adobe Elements when converting the RAW to PNG in
order
to rule out the possibility that IrfanView is fiddling with the pixel
values
(given that the version I use doesn't work with full size RAW's, only
half
size).

But, if I get the same results with Adobe, I'll try building in a
tolerance
and see if that works.

There's also the possibility of converting each pixel to BW and
comparing the brightness of the pairs and see if that comes closer to
an exact match.
If it does, then the original colour components could be manipulated
according to how bright they appear.


Ithat would be similar to the Adobe selection tool "magic wand," in
application. But, I think I understand why & how the script would help.



Yep, that's what I'm trying to achieve...

Since it's impossible for me to use the Adobe tools to work on selected
portions of images, I'm trying to develop a script that will work on an
entire image at once.

By taking two images, one with subject and one without, I'm hoping to
drop out the background and substitute a single shade of a colour not in
the subject. Then, that colour could be used as a mask in order to drop
in a different background. It could also be used as a template to
change the existing background to BW while leaving the subject as shot.

The possibilities are virtually limitless, and an extremely find
"cropping" of the subject could be achieved -- right down to the
individual hair level.

Assuming I can get it to work ...

Take Care,
Dudley



It sounds like you are making this job harder than it needs to be. Instead
of making the background a color and using it as a mask to modify another
image, simply make the background transparent. Layer the image with the
transparent background on top of your new background and you are done.

  #12  
Old August 15th 12, 07:03 PM posted to rec.photo.digital
Dudley Hanks[_4_]
external usenet poster
 
Posts: 1,282
Default Identical Pix


"Martin Brown" wrote in message
...
On 14/08/2012 23:36, Dudley Hanks wrote:
"PeterN" wrote in message
...
On 8/14/2012 6:10 PM, Dudley Hanks wrote:
"PeterN" wrote in message
...
On 8/14/2012 5:36 PM, Dudley Hanks wrote:
I had this great idea to write a Perl script to help isolate my
subjects
from their backgrounds...

I thought I could take two pics, one without the subject and one
with,
both
shot in manual mode with the same settings, shot only moments apart.

Then, I thought I could run through the pixels and change the pixels
that
were the same for a different background colour, leaving the subject
intact,
as it would have pixels different from the first image.

I assumed that the pixels should be the same in the background but
different
where the subject was situated.

Interestingly, even though there is no apparent difference when
viewed
side
by side, individual RGB values can vary by more than +/-25 per red,
green
or
blue component on virtually every pixel.


Sounds a bit high at 10% of amplitude - how were you registering the two
images against each other?

In spite of shooting in RAW and using lossless png source files, all
but
a
couple of hundred thousand pixels were unique between images.

I've only conducted the experiment after using Irfanview to convert
the
RAW
files to png, so it could be something in this particular
application.
I'll
check it out a bit more thoroughly, tomorrow, using Adobe, but it
looks
as
though each shot is truly unique, regardless of how similar they
might
appear.

BTW, as a control, I compared two copies of the same file, and as one
would
expect, the whole image went black, so it would seem that the script
is
working properly, it's just that the rgb values are unique when pics
are
shot moments apart.

Anyone out there have any experience with trying this technique, but
with
more success?

Take Care,
Dudley

I know this doesn't answer your question, but can you put a tolerance
factor in your script.


--
Peter

Yes, it's possible, but clumsy.

First, I want to try Adobe Elements when converting the RAW to PNG in
order
to rule out the possibility that IrfanView is fiddling with the pixel
values
(given that the version I use doesn't work with full size RAW's, only
half
size).

But, if I get the same results with Adobe, I'll try building in a
tolerance
and see if that works.

There's also the possibility of converting each pixel to BW and
comparing
the brightness of the pairs and see if that comes closer to an exact
match.
If it does, then the original colour components could be manipulated
according to how bright they appear.

Ithat would be similar to the Adobe selection tool "magic wand," in
application. But, I think I understand why & how the script would help.



Yep, that's what I'm trying to achieve...

Since it's impossible for me to use the Adobe tools to work on selected
portions of images, I'm trying to develop a script that will work on an
entire image at once.

By taking two images, one with subject and one without, I'm hoping to
drop
out the background and substitute a single shade of a colour not in the
subject. Then, that colour could be used as a mask in order to drop in a
different background. It could also be used as a template to change the
existing background to BW while leaving the subject as shot.

The possibilities are virtually limitless, and an extremely find
"cropping"
of the subject could be achieved -- right down to the individual hair
level.

Assuming I can get it to work ...


It sounds like you are trying to reinvent chroma key green/blue screen but
without thinking about the possibility that your static background may
change between shots. Even if you took a burst of shots the lighting will
change slightly and air currents will be enough to shift single pixels
around. You can see them rising off hot tarmac.

You will also be in trouble if your target happens to have any parts the
same colour as the background behind them!

Shifting the reference image around until the difference on non-target
bits is minimised will help remove systematic errors.

Regards,
Martin Brown



The blue screen idea is exactly what I'm after...

Given I can't see what's in backgrounds, and given I can't use editors like
Photoshop to get rid of distractions, I'm trying to find a "blind friendly"
method for cleaning up backgrounds. As noted before, I was hoping I could
take a pic of the background, move in the subject, and then use differences
between the two images to clean up distractions in the back.

While it's going to be rather tough, I haven't given up on the idea.

I think that my process will work with really high contrast images,
especially with backlit subjects.

But, I'm going to have to tweak my formula a lot.

Take Care,
Dudley


  #13  
Old August 16th 12, 09:18 PM posted to rec.photo.digital
Wolfgang Weisselberg
external usenet poster
 
Posts: 5,285
Default Identical Pix

Chris Malcolm wrote:

[The Programmer's Delusion: "This is a tedious process which will take
me a few hours of painstaking work. Hm. I could save myself a
lot of time by writing a program which would do it in less than a
minute!"


The delusion is of course not considering that saving a few hours of
tedious painstaking work will take several days of tedious painstaking
coding and debugging.]


The other delusions are that
a) (mostly) blind people can do such visual tedious
painstaking work --- especially in a few hours
b) such a task happens only so rarely that
"x * a few hours" "1 * several days" is still true
c) it's not a good use of time to create such a program because
people are only interested in photography
d) noone else would be interested in the working program, because
they all prefer painstaking work for hours instead of a one
minute program run

However, my guess is that you'd need to be well versed in machine
vision (and can build on the libraries of others in that area)
to manage to program sich a tool in several days. The obvious
naive solution, as Dudley found, doesn't work.

-Wolfgang
  #14  
Old August 17th 12, 12:13 AM posted to rec.photo.digital
Dudley Hanks[_4_]
external usenet poster
 
Posts: 1,282
Default Identical Pix


"Wolfgang Weisselberg" wrote in message
...
Chris Malcolm wrote:

[The Programmer's Delusion: "This is a tedious process which will take
me a few hours of painstaking work. Hm. I could save myself a
lot of time by writing a program which would do it in less than a
minute!"


The delusion is of course not considering that saving a few hours of
tedious painstaking work will take several days of tedious painstaking
coding and debugging.]


The other delusions are that
a) (mostly) blind people can do such visual tedious
painstaking work --- especially in a few hours
b) such a task happens only so rarely that
"x * a few hours" "1 * several days" is still true
c) it's not a good use of time to create such a program because
people are only interested in photography
d) noone else would be interested in the working program, because
they all prefer painstaking work for hours instead of a one
minute program run

However, my guess is that you'd need to be well versed in machine
vision (and can build on the libraries of others in that area)
to manage to program sich a tool in several days. The obvious
naive solution, as Dudley found, doesn't work.

-Wolfgang


Well put, Wolfgang. The hours of tedious work would have been worth it if
it works, since it would have enabled me to do something I can't currently
achieve the results I want.

I'm not sure whether I'm ready to entirely concede or not, as there may be
certain situations where I can get acceptable results with my current
skillset. But, it's only something I'm prepared to pursue in my spare time.

So, it's on the back burner for the foreseeable future...

Take Care,
Dudley


  #15  
Old August 18th 12, 11:11 AM posted to rec.photo.digital
Chris Malcolm[_2_]
external usenet poster
 
Posts: 3,142
Default Identical Pix

Wolfgang Weisselberg wrote:
Chris Malcolm wrote:


[The Programmer's Delusion: "This is a tedious process which will take
me a few hours of painstaking work. Hm. I could save myself a
lot of time by writing a program which would do it in less than a
minute!"


The delusion is of course not considering that saving a few hours of
tedious painstaking work will take several days of tedious painstaking
coding and debugging.]


The other delusions are that
a) (mostly) blind people can do such visual tedious
painstaking work --- especially in a few hours


You misunderstood. Of course I know Dudley can't do that kind of
thing. What I was suggesting was that for that reason some of the
"flying in the air" photographic tricksters might have developed some
simple software he could use.

b) such a task happens only so rarely that
"x * a few hours" "1 * several days" is still true
c) it's not a good use of time to create such a program because
people are only interested in photography


Unless of course they happen to be programmers with an interest in
machine vision :-)

--
Chris Malcolm
  #16  
Old August 18th 12, 11:25 PM posted to rec.photo.digital
Dudley Hanks[_4_]
external usenet poster
 
Posts: 1,282
Default Identical Pix


"Chris Malcolm" wrote in message
...
Wolfgang Weisselberg wrote:
Chris Malcolm wrote:


[The Programmer's Delusion: "This is a tedious process which will take
me a few hours of painstaking work. Hm. I could save myself a
lot of time by writing a program which would do it in less than a
minute!"


The delusion is of course not considering that saving a few hours of
tedious painstaking work will take several days of tedious painstaking
coding and debugging.]


The other delusions are that
a) (mostly) blind people can do such visual tedious
painstaking work --- especially in a few hours


You misunderstood. Of course I know Dudley can't do that kind of
thing. What I was suggesting was that for that reason some of the
"flying in the air" photographic tricksters might have developed some
simple software he could use.

b) such a task happens only so rarely that
"x * a few hours" "1 * several days" is still true
c) it's not a good use of time to create such a program because
people are only interested in photography


Unless of course they happen to be programmers with an interest in
machine vision :-)

--
Chris Malcolm




Well, I'm slowly figuring it out...

Last night, I shot a couple of pics of some graph paper at normal exposure,
then another couple at +1 stop.

A quick check of the colour values indicates that there is a closer
coralation between pixel values when the image is slightly over-exposed, and
I was able to use my script to completely "drop" one image out, with only a
+/-12 difference in RGB values.

Now, if I can just replicate that experiment with a more typical background
and a subject I'll be laughing ...

Take Care,
Dudley


 




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