Is Vuescan's "Neutral" color balance at fault?

  • Thread starter Thread starter ThomasH
  • Start date Start date
T

ThomasH

I observe this problem throughout several recent versions
of Vuescan:

Color balance Neutral (even with with media type = image)
causes in many cases shift in color balance! Finally
I have discovered that real neutral is... 'Manual' with
all three channels set to "1". This is an example:

http://www.pbase.com/phototalk_thh/vue_neutral_problem

Do I misunderstand the meaning of "neutral" color balance
or is it a bug?

Thanks,

Thomas
 
ThomasH said:
I observe this problem throughout several recent versions
of Vuescan:

Color balance Neutral (even with with media type = image)
causes in many cases shift in color balance! Finally
I have discovered that real neutral is... 'Manual' with
all three channels set to "1". This is an example:

http://www.pbase.com/phototalk_thh/vue_neutral_problem

Do I misunderstand the meaning of "neutral" color balance
or is it a bug?

Thanks,

Thomas
Click to expand...

Same here! Shouldn't manual with with red/green/blue at 1 = neutral?
It doesn't. Definite blue cast in neutral, compared to to manual
1/1/1. D.O. White balance also, seems to have magenta cast.

ONLY way I can get decent color balance is with color balance "none",
then apply levels per channel with very light (.01%) clip in PS. See
examples near bottom, at:

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=008DUB
 
Mendel Leisk said:
Same here! Shouldn't manual with with red/green/blue at 1 = neutral?
Click to expand...


I probably didn't name this option correctly. Neutral just means
"no change in color cast - use whatever color cast comes from
the scanner", except it boosts the overall intensity.

Regards,
Ed Hamrick
 
Ed Hamrick said:
I probably didn't name this option correctly. Neutral just means
"no change in color cast - use whatever color cast comes from
the scanner", except it boosts the overall intensity.
Click to expand...

Photoshop calls it Auto Contrast (but it also uses predefined clipping of
shadows and/or highlights which VueScan's Neutral doesn't, as it ignores
Black/White point settings). Contrast boost or contrast stretch seems closer
to what VueScan achieves, because the color balance should not change with
'Neutral'. Normalize Contrast comes close to what happens, but is not
strictly accurate either.

As for the histograms that Thomas linked to, in the one with the Neutral
setting the red channel *does* change position relative to the others in
comparison to the 'None' histogram above it. So it seems that something else
happened.

Bart
 
SNIP
Same here! Shouldn't manual with with red/green/blue at 1 = neutral?
Click to expand...

Not exactly the same result, but close. Neutral ignores the Black/White
point settings effectively setting them to zero. So it should be 'neutral'
to the existing color balance. Manual can still use Black/White point
settings, but other than that should respond also 'neutral' to existing
colorbalance with Red/Green/Blue set to 1.
It doesn't. Definite blue cast in neutral, compared to to manual
1/1/1. D.O. White balance also, seems to have magenta cast.
Click to expand...

White balance adapts to lighting conditions, and that usually fails with few
neutral (non-clipped!) highlights. In Thomas' example only the puffs of
smoke/condensation seem somewhat white.
ONLY way I can get decent color balance is with color balance "none",
then apply levels per channel with very light (.01%) clip in PS. See
examples near bottom, at:

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=008DUB
Click to expand...

You can also set Input|Lock Image color, and tweak the Black/White points.
Setting the Prefs|Histogram type to Logarithmic will allow to fine-tune the
extremes with low pixel counts much better.

It can also help to temporarily crop a very small area of known non-clipped
neutral color, and scan at the highest resolution (you can temporarily
change the Crop|Preview area to Current to speed up due to only scanning the
cropped area). This will usually produce a histogram like a hump that should
have a similar peak for R/G/B for neutral appearence, and you can also
tweak-in a small cast (e.g. slightly reduced red peak for open sky shadow
under foliage).

Bart
 
SNIP
Photoshop calls it Auto Contrast (but it also uses predefined clipping of
shadows and/or highlights which VueScan's Neutral doesn't, as it ignores
Black/White point settings).
Click to expand...

It appears that the Black/White point settings ARE used an can cause
clipping, even with 'Neutral' Color balance. I thought that that wasn't the
case in the past, but I probably remembered wrong. The help file confirms
that only the relative position of the histograms remains intact.

Bart
 
Bart van der Wolf said:
SNIP

Not exactly the same result, but close. Neutral ignores the Black/White
point settings effectively setting them to zero. So it should be 'neutral'
to the existing color balance.
Click to expand...

CORRECTION, you are correct, I remembered wrong.
Manual can still use Black/White point
settings, but other than that should respond also 'neutral' to existing
colorbalance with Red/Green/Blue set to 1.
Click to expand...

Bart
 
I agree, the more previously Neutral color balance was what
Manual is now with its active right click selection of gray
point. Let remind that the introduction of Manual vs. Neutral
is a relatively recent change in Vuescan.

Anyway, it really helps me to know about the difference.
many images, especially these late afternoon or evening
low light temperature scenes can be reproduced very well
with the Manual-1-1-1 setting. Prior to this discovery
I used to grab an older Vuescan version without the
"new Neutral" color balance.

Thanks,

Thomas
 
I agree, the more previously Neutral color balance was what
Manual is now with its active right click selection of gray
point. Let remind that the introduction of Manual vs. Neutral
is a relatively recent change in Vuescan.

Anyway, it really helps me to know about the difference.
many images, especially these late afternoon or evening
low light temperature scenes can be reproduced very well
with the Manual-1-1-1 setting. Prior to this discovery
I used to grab an older Vuescan version without the
"new Neutral" color balance.

Thanks,

Thomas
 
I agree, the more previously Neutral color balance was what
Manual is now with its active right click selection of gray
point. Let remind that the introduction of Manual vs. Neutral
is a relatively recent change in Vuescan.

Anyway, it really helps me to know about the difference.
many images, especially these late afternoon or evening
low light temperature scenes can be reproduced very well
with the Manual-1-1-1 setting. Prior to this discovery
I used to grab an older Vuescan version without the
"new Neutral" color balance.

Thanks,

Thomas
 
Back
Top