Vuescan and film base colour determination

[Pedro Gomez]

Hi,

I've been following the "advanced workflow suggestions" in order to
determine the proper RGB & FBC exposure for my slide scans and I've
found something which I don't quite understand:
If I use an exposed frame with a white area on it, the fbc that I get
seems to produce more accurate colour results that if I use the leader
(clearest part) of the slide film. As a matter of fact, it doesn't
matter whether I make a crop on the whitest area or select the entire
frame for fbc determination.

Can anybody provide an explanation for this?
Thanks
Pedro.

PS. I'm using the following settings
Device|type = slide
Color|slide type = generic
Color|white balance = neutral

 

[Erik Krause]

Hello, Pedro Gomez
you wrote...

I've been following the "advanced workflow suggestions" in order to
determine the proper RGB & FBC exposure for my slide scans and I've
found something which I don't quite understand:
If I use an exposed frame with a white area on it, the fbc that I get
seems to produce more accurate colour results that if I use the leader
(clearest part) of the slide film.

Did you verify that the leader was exposed by daylight? I often have
film leaders that are yellow instead of clear since I changed film in
incandescent light conditions.

As a matter of fact, it doesn't
matter whether I make a crop on the whitest area or select the entire
frame for fbc determination.

If I understood correctly vuescan searches for the brightest area to
determine film base color. But sometimes I found it gets different
results depending on whether I cropped to the brightest area or used
the whole frame. There seems to be a minimum percentage or similar. May
be Ed can comment...

 

[Pedro Gomez]

Hi Erik, thanks for the response

Hello, Pedro Gomez
you wrote...


Did you verify that the leader was exposed by daylight? I often have
film leaders that are yellow instead of clear since I changed film in
incandescent light conditions.

That is indeed the case for a few of my leaders, they have a yellow
cast at one end which I try to avoid when cropping. But many others
look quite transparent to me and still I don't get a proper fbc.
¿Could this be related to the fact that the scanner is still not warm
enough? Personally I doubt it since I'm using an LS4000 which, if I
remember well, uses leds as a lightsource. ¿Any other idea?