what 'auto-exposure' does?

[Steven Woody]

for scanning film, it seems some scanner software gets a feature of
'auto-exposure'. what this function does? is it anything to do with
level adjustment?

thanks.

 

[CSM1]

for scanning film, it seems some scanner software gets a feature of
'auto-exposure'. what this function does? is it anything to do with
level adjustment?

thanks.

It works similar to the way auto exposure works on a digital camera.

It attempts to find the correct exposure to get the widest range of whites
and blacks while putting the middle grays at around the middle of the data
range.

If the range is 0-255 (8 bits per channel) then middle gray will hit close
to 128.

At least that is what auto exposure tries to do.

Auto exposure usually works very well. But not with all film.

 

[Steven Woody]

It works similar to the wayautoexposureworks on a digital camera.

we know 'exposure' means letting special amount of light hitting on
the film ( paper or ccd ), but what does 'exposure' means to a
scanner? i think i have to get know what is exposure before
understand 'auto exposure' in a scanner.

if 'auto exposure' here in scanner really similar to 'auto exposure'
on digital camera, so scanner have to adjust the amount of light it
emitted from the its light source. is it true or 'auto exposure' only
a 'level adjustment' game?

thanks.

-
woody

 

[Ken Weitzel]

we know 'exposure' means letting special amount of light hitting on
the film ( paper or ccd ), but what does 'exposure' means to a
scanner? i think i have to get know what is exposure before
understand 'auto exposure' in a scanner.

if 'auto exposure' here in scanner really similar to 'auto exposure'
on digital camera, so scanner have to adjust the amount of light it
emitted from the its light source. is it true or 'auto exposure' only
a 'level adjustment' game?

Hi..

A "level adjustment" game.

Take care.

Ken

 

[Steven Woody]

Hi..

A "level adjustment" game.

Take care.

Ken

thanks. so, can i deduce that a scanner always emit fixed amount of
light, and 'exposure adjustment' can always be done post-scan in a
dedicated photo editor program ( supposing scanner and photo editor
are both 16bit per channel)? in particular, i use a Epson 4870 flat
bed scanner for scanning films.

thanks.

-
woody

 

[Ken Weitzel]

thanks. so, can i deduce that a scanner always emit fixed amount of
light, and 'exposure adjustment' can always be done post-scan in a
dedicated photo editor program ( supposing scanner and photo editor
are both 16bit per channel)? in particular, i use a Epson 4870 flat
bed scanner for scanning films.

Hi...

No no no, absolutely not!

Yes, the light source is always (virtually) the same, but before
you get the output software "tampers" with it. You must do the best
you can at each and every stage of the process.

Let me suggest an analogy if I may. You're recording some music with
a tape recorder. During the recording process you've recorded at
much too high a setting, resulting in distortion during the loud
passages. That's what you've recorded. During playback
(post-processing) you can turn the volume down to a reasonable
level, making it more acceptable, but the recorded distortion will
still and always be there, and can't possibly be "repaired".

The other side of that would be to have recorded it much too low,
in which case post processing would involve turning up the listening
volume - which would dramatically increase the noise.

I don't have your machine, still back at a 3200 photo, and here's
what I do. I prescan a piece of film, click auto - but just to get
quickly into the ball park - then I look at the histogram and make
minor corrections. (Epson's - at least all I've known - always slightly
blow out highlights in auto, so you'll surely want to pull them down)

As for the 16 bit, remember that you may scan at 16, and some editing
software may handle 16 bit, but you can't see it on your monitor, so...

Hope this helps a bit.

Take care.

Ken

 

[Steven Woody]

Hi...

No no no, absolutely not!

Yes, the light source is always (virtually) the same, but before
you get the output software "tampers" with it. You must do the best
you can at each and every stage of the process.

Let me suggest an analogy if I may. You're recording some music with
a tape recorder. During the recording process you've recorded at
much too high a setting, resulting in distortion during the loud
passages. That's what you've recorded. During playback
(post-processing) you can turn the volume down to a reasonable
level, making it more acceptable, but the recorded distortion will
still and always be there, and can't possibly be "repaired".

The other side of that would be to have recorded it much too low,
in which case post processing would involve turning up the listening
volume - which would dramatically increase the noise.

I don't have your machine, still back at a 3200 photo, and here's
what I do. I prescan a piece of film, click auto - but just to get
quickly into the ball park - then I look at the histogram and make
minor corrections. (Epson's - at least all I've known - always slightly
blow out highlights in auto, so you'll surely want to pull them down)

As for the 16 bit, remember that you may scan at 16, and some editing
software may handle 16 bit, but you can't see it on your monitor, so...

Hope this helps a bit.

Take care.

so, what settings on the scanner software really affect how the
'recording' will be high or low? thanks.

-
woody

 

[CSM1]

Hi...

No no no, absolutely not!

Yes, the light source is always (virtually) the same, but before
you get the output software "tampers" with it. You must do the best
you can at each and every stage of the process.

Let me suggest an analogy if I may. You're recording some music with
a tape recorder. During the recording process you've recorded at
much too high a setting, resulting in distortion during the loud
passages. That's what you've recorded. During playback
(post-processing) you can turn the volume down to a reasonable
level, making it more acceptable, but the recorded distortion will
still and always be there, and can't possibly be "repaired".

The other side of that would be to have recorded it much too low,
in which case post processing would involve turning up the listening
volume - which would dramatically increase the noise.

I don't have your machine, still back at a 3200 photo, and here's
what I do. I prescan a piece of film, click auto - but just to get
quickly into the ball park - then I look at the histogram and make
minor corrections. (Epson's - at least all I've known - always slightly
blow out highlights in auto, so you'll surely want to pull them down)

As for the 16 bit, remember that you may scan at 16, and some editing
software may handle 16 bit, but you can't see it on your monitor, so...

Hope this helps a bit.

Take care.

so, what settings on the scanner software really affect how the
'recording' will be high or low? thanks.

-
woody


That depends on the scanner and scanner software.

Some scanners have "level" some have "gain" some have "Tone Curves" and some
have a histogram. Some have a Brightness and Contrast control.

And some have a combination of those features.

As a general rule the adjustments are in some advanced or Professional mode
of the scanner software.

Canon calls it Advanced Mode, Epson calls it Professional mode.

Other brands may have their own names for the "not a dummy" mode.

 

[Roger S.]

Isn't exposure the length of time a fixed amount of light is shone
through the film? Doesn't analog gain control this duration on a per
channel basis on the Nikons?

Exposure problems are not necessarily correctable with software
adjustments post-scan.

 

[Ken Weitzel]

so, what settings on the scanner software really affect how the
'recording' will be high or low? thanks.

-
woody


That depends on the scanner and scanner software.

Some scanners have "level" some have "gain" some have "Tone Curves" and some
have a histogram. Some have a Brightness and Contrast control.

And some have a combination of those features.

As a general rule the adjustments are in some advanced or Professional mode
of the scanner software.

Canon calls it Advanced Mode, Epson calls it Professional mode.

Other brands may have their own names for the "not a dummy" mode.

Hi...

With Epson's, in the professional mode, he can do his prescan, then mask
what he wants. Next click zoom to get a prescan of only the masked areas.

Then he should click auto as the easiest and fastest way to get himself
into the general ballpark.

Beside the auto button is a histogram button, which will show him a
histogram with (un-named) black, white, and gamma sliders under it.
He'll almost certainly want to pull the white down considerably.

Besides the auto and histogram buttons are two more. One is for
curves, and offers several predefined curves as well as do it yourself.
The fourth allows manual correction of all sorts of things...
brightness, contrast, saturation, etc., as well as color correction.

Take care.

Ken

 

[Steven Woody]

Hi...

With Epson's, in the professional mode, he can do his prescan, then mask
what he wants. Next click zoom to get a prescan of only the masked areas.

Then he should click auto as the easiest and fastest way to get himself
into the general ballpark.

Beside the auto button is a histogram button, which will show him a
histogram with (un-named) black, white, and gamma sliders under it.
He'll almost certainly want to pull the white down considerably.

Besides the auto and histogram buttons are two more. One is for
curves, and offers several predefined curves as well as do it yourself.
The fourth allows manual correction of all sorts of things...
brightness, contrast, saturation, etc., as well as color correction.

Take care.

Ken

so i am getting to know, what folks said 'auto exposure' is just
'auto' which might simply mean a collection of scanning options, when
you use 'auto', you use the collection of defaults. am i right? if
so, 'auto exposure' is a wrong word creating confuse.

and, my real concerns is if or not those controls provided in the
scanner's TWAIN interface, such as level/curve adjustment, put any
*real* effects on how the scanner scan a film. here, i define what i
mentioned 'real effects' as

real effects: via adjusting the TWAIN controls, what the scanner
software put on the scanner hardware and change its way of scanning.
for example, resolution seting will put a real effects.

non-real effects: via adjusting the TWAIN controls, what the scanner
software put on the ( temporary ) output image file ( might in its raw
format ) which actually can instead be done postly in a dedicated
photo editor program.

so my, question is, do the below controls provide real effects?

1, auto
2, level adjustment ( black point, white point, gray point )
3, brightness
4, color balance

i hop you understan, i am actually qustioning what can not be done in
Photostop and hence should be done at first time in the TWAIN.
thanks.

-
woody

 

[Ken Weitzel]

so i am getting to know, what folks said 'auto exposure' is just
'auto' which might simply mean a collection of scanning options, when
you use 'auto', you use the collection of defaults. am i right? if
so, 'auto exposure' is a wrong word creating confuse.

and, my real concerns is if or not those controls provided in the
scanner's TWAIN interface, such as level/curve adjustment, put any
*real* effects on how the scanner scan a film. here, i define what i
mentioned 'real effects' as

real effects: via adjusting the TWAIN controls, what the scanner
software put on the scanner hardware and change its way of scanning.
for example, resolution seting will put a real effects.

non-real effects: via adjusting the TWAIN controls, what the scanner
software put on the ( temporary ) output image file ( might in its raw
format ) which actually can instead be done postly in a dedicated
photo editor program.

so my, question is, do the below controls provide real effects?

1, auto
2, level adjustment ( black point, white point, gray point )
3, brightness
4, color balance

i hop you understan, i am actually qustioning what can not be done in
Photostop and hence should be done at first time in the TWAIN.
thanks.

Hi...

I think we're having a little trouble with words...

First, and I know I repeat myself, but do the BEST you can in each
step of the process... from first scanning to printing. We know that
two wrongs can't make a right (maybe a better?), but surely can't be
better than two rights

Auto, auto exposure, whatever you choose to call it, isn't a collection
of defaults - rather it's calculated or measured responses to various
"tests" the software makes while "looking" at the picture. For
instance, it will look for the brightest spot in the picture, and make
that spot the brightest. (white point) It will look for the least
colorful pixel,and make that colorless. As well as many other tests, of
course. It *will* sooner or later make mistakes... for instance, only
this afternoon I took pictures of my youngest grandchild making snow
angels for me in the front yard. Very little in the picture. Lots and
lots of snow, lots of red snowsuit, boots, mittens, scarf. A tiny bit
of flesh colored face. Those pics were digital, but had they been film,
and then scanned the scanner's "auto" would get terribly confused.
As did the camera

You mention "how the scanner scans the film". We have to remember that
the output from the sensors is followed by analogue amplifiers, and
your settings will change the gain (amplification) of those amplifiers.
So - if one, or two, or all three are for instance waaaay to high, then
like the distorted audio which *can't* be corrected, the white point
will be waaay to high, and can't be corrected. Made better in post
processing perhaps, but not nearly anywhere as good as were it done
properly in the first place.

At this point, all we have is three analogue voltages - of little or
no use to us. Internal to the scanner is "post scanning" software,
some of which we can control via twain settings. (the twain driver tells
the scanner of our wishes). It must be converted to 8 or 16 bit
digital, and some of our wishes are then obeyed... such as a desire to
sharpen, or unsharp mask.

Hope this helps.

Take care.

Ken

 

[Roger S.]

Or the short answer- get the exposure right, output 16 bit files and
do the rest in Photoshop.

 

[Steven Woody]

Hi...

I think we're having a little trouble with words...

First, and I know I repeat myself, but do the BEST you can in each
step of the process... from first scanning to printing. We know that
two wrongs can't make a right (maybe a better?), but surely can't be
better than two rights

Auto, auto exposure, whatever you choose to call it, isn't a collection
of defaults - rather it's calculated or measured responses to various
"tests" the software makes while "looking" at the picture. For
instance, it will look for the brightest spot in the picture, and make
that spot the brightest. (white point) It will look for the least
colorful pixel,and make that colorless. As well as many other tests, of
course. It *will* sooner or later make mistakes... for instance, only
this afternoon I took pictures of my youngest grandchild making snow
angels for me in the front yard. Very little in the picture. Lots and
lots of snow, lots of red snowsuit, boots, mittens, scarf. A tiny bit
of flesh colored face. Those pics were digital, but had they been film,
and then scanned the scanner's "auto" would get terribly confused.
As did the camera

thank you, Ken. you mentioned, 'auto' will have the scanner exame or
'look' the picture and guess what convertion it will do ( make what as
white and what as black ). do i understand right? the problem is,
what 'picture' it look? the original on the film or just the output
raw data from the ccd? if answer is the latter, so i think this kind
of 'look' or exam is of little use because we can do it postly in
photo editor, and by this way we get advance of keeping an origial
output of scanner in case sometimes latter we change our decisions
about settings ).

You mention "how the scanner scans the film". We have to remember that
the output from the sensors is followed by analogue amplifiers, and
your settings will change the gain (amplification) of those amplifiers.
So - if one, or two, or all three are for instance waaaay to high, then
like the distorted audio which *can't* be corrected, the white point
will be waaay to high, and can't be corrected. Made better in post
processing perhaps, but not nearly anywhere as good as were it done
properly in the first place.

Yep! i think the amplication ( gain ) is what i mostly concern. what
controls let me change the scanner gain used in scanning? supposing
you put a negative on the bed and you pressed preview before checking
the histgram, you found the high value end gets some extends of clips,
then you decided to move the white point a little right, will this
operation improve the gain and give you more data avaliabe in
highlights areas? the same question applies to brightness control.

 

[Roger S.]

Yep! i think the amplication ( gain ) is what i mostly concern. what
controls let me change the scanner gain used in scanning?

gain = exposure. There should be a way to disable autoexposure. I
use Vuescan so I don't know your software. The Vuescan "advanced
workflow" lets you manually select an exposure- one setting should do
it for a given type of color negative film.

supposingyou put a negative on the bed and you pressed preview before checking
the histgram, you found the high value end gets some extends of clips,
then you decided to move the white point a little right, will this
operation improve the gain and give you more data avaliabe in
highlights areas?

No, not at all. If you truly looked at the actual scan data you would
see a very flat looking image with weak blacks and no whites (after
gamma correction and removing the orange mask). Setting white and
black point is done in software and can be done as well in Photoshop.
If you need to increase gain (exposure) to get above your scanner's
noise floor there's no reason you can't just pick one exposure and
scan all C-41 negatives the same way as their dynamic range is far
less than that of the scanner. B&W and slides are different as they
have larger density ranges.

the same question applies to brightness control.

Again, post-exposure software corrections.

 

[Steven Woody]

gain = exposure. There should be a way to disable autoexposure. I
use Vuescan so I don't know your software. The Vuescan "advanced
workflow" lets you manually select an exposure- one setting should do
it for a given type of color negative film.


No, not at all. If you truly looked at the actual scan data you would
see a very flat looking image with weak blacks and no whites (after
gamma correction and removing the orange mask). Setting white and
black point is done in software and can be done as well in Photoshop.
If you need to increase gain (exposure) to get above your scanner's
noise floor there's no reason you can't just pick one exposure and
scan all C-41 negatives the same way as their dynamic range is far
less than that of the scanner. B&W and slides are different as they
have larger density ranges.


Again, post-exposure software corrections.

thanks Roger. from what you said, i now know level/curve/brightness
controls are all post-exposure software corrections, which indeed
confirms my guess.

one thing i still not clear, what controls determind the 'exposure'?
it's okay you show it using VueScan.

-
woody

 

[CSM1]

thanks Roger. from what you said, i now know level/curve/brightness
controls are all post-exposure software corrections, which indeed
confirms my guess.

one thing i still not clear, what controls determind the 'exposure'?
it's okay you show it using VueScan.

-
woody

I think somebody needs to get an education about the in and outs of
scanning.

Go the the best site on the internet to learn about and how to do scanning.
http://www.scantips.com

 

[Steven Woody]

I think somebody needs to get an education about the in and outs of
scanning.

Go the the best site on the internet to learn about and how to do scanning.http://www.scantips.com

i've read some of it, but not seems an answer of my question

 

[Roger S.]

Is there nothing that says gain -1 0 +1 +2? My Canon twain software
has this.
Vuescan lets you "lock exposure" and insert a value like 1, 2, 3, with
2 giving you twice the exposure length as 1 for example. Disable
"auto" and see if anything like this appears.

If you can move the white point/ black point sliders to the ends so
that there is a valley, a peak where your image data is, and then
another long valley you will know you're not losing data. Increasing
or decreasing exposure should just move the peak left or right. For
negatives, expose to the left. For slides, keep the values as far to
the right as you can without clipping the highlights.

Levels, curves, etc just stretches this data out. The goal of
scanning is to get the best possible data so you can stretch it and
still preserve good image quality.

 

[Ken Weitzel]

Is there nothing that says gain -1 0 +1 +2? My Canon twain software
has this.
Vuescan lets you "lock exposure" and insert a value like 1, 2, 3, with
2 giving you twice the exposure length as 1 for example. Disable
"auto" and see if anything like this appears.

If you can move the white point/ black point sliders to the ends so
that there is a valley, a peak where your image data is, and then
another long valley you will know you're not losing data. Increasing
or decreasing exposure should just move the peak left or right. For
negatives, expose to the left. For slides, keep the values as far to
the right as you can without clipping the highlights.

Levels, curves, etc just stretches this data out. The goal of
scanning is to get the best possible data so you can stretch it and
still preserve good image quality.

Hi...

The epson software histogram has number entry boxes underneath the
histogram that you may use instead of the sliders... calibrated
from 0 to 255.

Take care.

Ken