Computer Graphics with Photoshop

Author

intersect pictures

Johannes Vogel

2006-05-07, 10:16 pm

Hi

I have the same picture twice. First has an object included, second
hasn't it. The Pictures are exactly the same (screen shots). Now I would
like to intersect them, so I have only the object as result. The rest
should be transparent (or one single color, so I can clear it). How can
I do this? I'm using Photoshop CS 8.

Thanks for any advise!
Johannes

2006-05-07, 10:16 pm

"Johannes Vogel" <newsgroups@jvogel.ch> wrote in message
news:2628f$445e83a4$544a5360$16447@news.hispeed.ch...
> Hi
>
> I have the same picture twice. First has an object included, second
> hasn't it. The Pictures are exactly the same (screen shots). Now I would
> like to intersect them, so I have only the object as result.

Translate that. Offhand, it seems you want them on different layers with the
blend mode to exclude the same pixels. Right?

Johannes Vogel

2006-05-07, 10:16 pm

Hi 2

Thanks for your fast answer!

2 wrote:
> "Johannes Vogel" <newsgroups@jvogel.ch> wrote:
> Translate that. Offhand, it seems you want them on different layers with the
> blend mode to exclude the same pixels. Right?

Exactly! I have them in different layers.
In the first layer I have some pixels different than in the other layer.
Now I would like to extract only all different pixels.

Perhaps this simple code would help:
for each pixel as i
if pixA(i) is equal to pixB(i) then
clear
else
take pixA(i)

I looked in the blending options, but couldn't find, what I want. If the
pixel in layer A is different to the same one in layer B, nothing should
be changed on the pixel (i.e. no color change), but if they are the
same, then clear this pixel. In blending options I only found some
options which changed the color anyway...

Thanks for any advise!
Johannes

2006-05-07, 10:16 pm

"Johannes Vogel" <newsgroups@jvogel.ch> wrote

> I looked in the blending options, but couldn't find, what I want. If the
> pixel in layer A is different to the same one in layer B, nothing should
> be changed on the pixel (i.e. no color change), but if they are the
> same, then clear this pixel. In blending options I only found some
> options which changed the color anyway...

Johannes: Select a layer in the layers pallet. Then click in the layers
palette on Mode so that the text turns black. Then use your arrow-key do
march down (and up) and you will see the layer in the various modes
available. It's a good feature. Hope this helps.

Peter Wollenberg

2006-05-08, 3:16 am

Johannes Vogel <newsgroups@jvogel.ch> wrote:

>Hi
>
>I have the same picture twice. First has an object included, second
>hasn't it. The Pictures are exactly the same (screen shots). Now I would
>like to intersect them, so I have only the object as result. The rest
>should be transparent (or one single color, so I can clear it). How can
>I do this? I'm using Photoshop CS 8.
>
>Thanks for any advise!
>Johannes

Put the image with the object on top of the background image. Set the
top layer mode to difference. All identical pixels should turn
black.Now use the magic wand in the contiguous mode to select the
black surrounding the object. Set the tolerance of the magic wand to a
level as low as possible. If the images are not exactly identical, it
may be helpful to copy the merged images to a new layer, then, using
the levels dialogue, increase the contrast, so that the background is
actually pure black. If you got the proper selection, you can trash
the auxilliary layer and clear the background from the layer with the
image. This layer will contain the object on a transparent background.
It may be necessary to defringe the object or to feather the selection
slightly before you remove the background
HTH,
viele Gruesse in die Schweiz! Peter

Johannes Vogel

2006-05-08, 6:16 pm

Hi Peter

Peter Wollenberg wrote:
> Johannes Vogel <newsgroups@jvogel.ch> wrote:
> Put the image with the object on top of the background image. Set the
> top layer mode to difference. All identical pixels should turn
> black.Now use the magic wand in the contiguous mode to select the
> black surrounding the object. Set the tolerance of the magic wand to a
> level as low as possible. If the images are not exactly identical, it
> may be helpful to copy the merged images to a new layer, then, using
> the levels dialogue, increase the contrast, so that the background is
> actually pure black. If you got the proper selection, you can trash
> the auxilliary layer and clear the background from the layer with the
> image. This layer will contain the object on a transparent background.
> It may be necessary to defringe the object or to feather the selection
> slightly before you remove the background

Thank you very much for your help. It works fine for me!
Grüsse zurück ins grosse Deutschland.. :-)
Johannes

Johannes Vogel

2006-05-08, 6:16 pm

Hi 2

2 wrote:
> "Johannes Vogel" <newsgroups@jvogel.ch> wrote
> Johannes: Select a layer in the layers pallet. Then click in the layers
> palette on Mode so that the text turns black. Then use your arrow-key do
> march down (and up) and you will see the layer in the various modes
> available. It's a good feature. Hope this helps.

Yes, it helps. I needed the difference to set the correct selection,
then I could remove the overlay mask and cleared all unneaded pixels in
the original pictures. Thak you very much for your fast help!

Johannes

Falco98

2006-05-10, 3:18 am

Johannes Vogel wrote:
> Hi
>
> I have the same picture twice. First has an object included, second
> hasn't it. The Pictures are exactly the same (screen shots). Now I would
> like to intersect them, so I have only the object as result. The rest
> should be transparent (or one single color, so I can clear it). How can
> I do this? I'm using Photoshop CS 8.
>
> Thanks for any advise!
> Johannes

I'm more of a novice than others here, but as noone has replied yet I'll
give it a shot.
Firstly, the images both have to be *incredibly* alike -- aligned even
to the pixel for good results. Assuming they are, or you can at least
crop them until this is true, then this might work.

Open both the images as 2 layers in a new photoshop project. Have the
one without the object be the "top" layer. After that, I believe it
*MAY* be as simple as changing the "overlay mode" for the top image to
something fancy (i'm thinking "add" or "subtract" or "dissolve" or
"overlay" or one of thems -- but like i said i'm a novice, and i'd have
to guess. good luck =)