Hi,

unfortunately it is not that easy, because not only have you to invert the colors, but to "subtract" the brown color from the film strip also. I'm not sure, but my first guess would be that this is not easily done in GIMP.

Greetings, lexA

Am 17.04.2007 um 22:02 schrieb Joao Moreira:

Hi,

I just took some photos negatives (memories from the pre-digital days :-) and
put them on my flat bed scanner. So now I have a color image of these negatives
in the gimp, so how do I go about turning them into a positive ?

I would expect this to be a very simple operation, like a subtraction, on each
pixel, right ? does this exist ? is there a tool/filter that does this ?

Or do I need to code a plugin, and if so, what exactly is the operation
to be done
(in terms of RGB) ?

Thanks,
Joao

Hi,

On Tue, 2007-04-17 at 22:58 +0200, Axel Wernicke wrote:

unfortunately it is not that easy, because not only have you to invert the colors, but to "subtract" the brown color from the film strip also. I'm not sure, but my first guess would be that this is not easily done in GIMP.

It should be easy though to write a plug-in that does this. One just needs to figure out the right values. Perhaps there are ICC color profiles for common brands of negatives that could help with this task?

Sven

Am 17.04.2007 um 23:16 schrieb Sven Neumann:

Hi,

On Tue, 2007-04-17 at 22:58 +0200, Axel Wernicke wrote:

unfortunately it is not that easy, because not only have you to invert the colors, but to "subtract" the brown color from the film strip also. I'm not sure, but my first guess would be that this is not easily done in GIMP.

It should be easy though to write a plug-in that does this. One just needs to figure out the right values. Perhaps there are ICC color profiles for common brands of negatives that could help with this task?

There are some papers, so there is a solution :)

http://www.c-f-systems.com/PhotoMathDocs.html

Just "somebody" needed to implement it :) And yes there is a Photoshop Plug-in already.

just my 2c lexA

Sven

---
Remember: There are only two tools in life. WD-40, for when something doesn't move, and should, and Duct Tape, for when something is moving and it shouldn't.
So does the universe explode if you spray duct tape with WD-40?

On Tue, 17 Apr 2007 22:02:51 +0200 Joao Moreira wrote:

Hi,

I just took some photos negatives (memories from the pre-digital days :-) and
put them on my flat bed scanner. So now I have a color image of these negatives
in the gimp, so how do I go about turning them into a positive ?

I would expect this to be a very simple operation, like a subtraction, on each
pixel, right ? does this exist ? is there a tool/filter that does this ?

Or do I need to code a plugin, and if so, what exactly is the operation to be done
(in terms of RGB) ?

Image->Layers->Colors->Invert ?

Owen

On Tue, Apr 17, 2007 at 11:16:28PM +0200, Sven Neumann wrote:

Hi,

On Tue, 2007-04-17 at 22:58 +0200, Axel Wernicke wrote:

unfortunately it is not that easy, because not only have you to invert the colors, but to "subtract" the brown color from the film strip also. I'm not sure, but my first guess would be that this is not easily done in GIMP.

It should be easy though to write a plug-in that does this. One just needs to figure out the right values. Perhaps there are ICC color profiles for common brands of negatives that could help with this task?

XSane maintains a list of known values. Actually, most scanning software (including XSane) will fix it for you if you tell it you are scanning a negative.

Owen wrote:

Or do I need to code a plugin, and if so, what exactly is the operation to be done
(in terms of RGB) ?

Image->Layers->Colors->Invert ?

Actually it's not that easy, because the film contains a mask (yellow & red), which has to be filtered out.

Claus

Claus Cyrny wrote:

Owen wrote:

Or do I need to code a plugin, and if so, what exactly is the operation to be done
(in terms of RGB) ?

Image->Layers->Colors->Invert ?

Actually it's not that easy, because the film contains a mask (yellow & red), which has to be filtered out.

Claus

And different films have different masks. Kodak is different from Fuji.

Like others have said, you were probably better off to have done this while scanning using either xsane or vuescan (not open source, but a pretty good scanner prog). I'm surprised whatever s/w you were using didn't give you the option when you told it you were scanning color negs.

jim

Joao Moreira wrote:

jim feldman wrote:

Like others have said, you were probably better off to have done this while scanning using either xsane or vuescan (not open source, but a pretty good scanner prog). I'm surprised whatever s/w you were using didn't give you the option when you told it you were scanning color negs.

I have an HP LaserJet 3057, and I just did "Acquire" in the gimp... but maybe
the option was there, I don't remember. I'll try that again, though.

I'd like to thank Alex for the link to www.c-f-systems.com, they have a paper
there, called "Negative to positive", that seems to explain it all. But it is
definitely NOT simple !

Thanks all, Joao

Isn't that a multifunction "reflective" scanner? I didn't know it did transparencies. I believe you were probably using the xsane plugin for the gimp to do the scan. It probably didn't prompt you for film type since it didn't think you would be scanning film on that model.