digital pre-exposure

RalphLambrecht · Apr 30, 2014

with film, shadow detail could be increased by givingthe film a weaker pre exposureprior to the image exposure.does this technique work with digital sensors too?

jeffreyg · Apr 30, 2014

Ralph,

This might not be the answer to your question but wouldn't HDR be similar?

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Hatchetman · Apr 30, 2014

Yes, take two exposures and merge them somehow. Tone mapping? I don't know HOW to do it, I just know it can be done.

Doyle Thomas · Apr 30, 2014

what you are talking about was called "pre-flashing". an exposure of a gray card was made at about 3 stops under before (or after) to raise the toe on the film exposure HD (Hutter Durfield I think it was) )curve. this could improve the shadow detail by about 2/3s stop at the cost of about 1/3 stop in the highlights. it has no function on a digital sensor.

indigo · Apr 30, 2014

Ralph,
I don't think digital sensor has the toe like film so I don't think it would work.

RalphLambrecht · May 2, 2014

my Nikon D800 has a multiexposure function.so,I'll try it.I'm hoping it could improve the signal/noise thresholdand improve or decrease shadow noise.it's worth a try

L Gebhardt · May 5, 2014

You want to look at HDR techniques. Also, if you aren't exposing to the right, that would be the first thing I would recommend to decrease the noise in the shadows. With the D800E I have had very few cases where HDR was required, or the shadow noise was too high when the exposure was biased towards fully exposed. Of course raw is required to make this work.

RalphLambrecht · May 5, 2014

I'm hoping for something less involved than HDR. a simple latent under exposure,to get the signal reception going,followed by a proper exposure,very similar to an analog pre-exposure would be simpler than HDR and potentially has the same benefit.I'll try my Nikon;s multi exposure feature and see how well that works before going to HDR.EVEN ADR seems to help quite a bit.HDR is an overrated fad.

Doyle Thomas · May 6, 2014

the sensor does not work in the same way film does. pre-flashing a grey card as part of a double exposure will reduce contrast because the sensor starts "fresh" with each exposure. when you pre-flash a piece of film each grain gets a little light struck. then, due to the law of diminishing returns aka reciprocity during the second exposure, more of the film grains in the shadows become sensitized. this also happens in the highlights but because so many more grains in the highlights become sensitized anyway it is less noticeable than what happens in the shadows. its an interesting idea Ralph and easy to try so go for it but I think you will find the results disappointing.

As Geb says,

"You want to look at HDR techniques. Also, if you aren't exposing to the right, that would be the first thing I would recommend to decrease the noise in the shadows. With the D800E I have had very few cases where HDR was required, or the shadow noise was too high when the exposure was biased towards fully exposed. Of course raw is required to make this work."

RalphLambrecht · May 7, 2014

Well,Itried it and you're right;I doesn't work,only HDR seems to work, but it was worth a try.while n the subject of reciprocity,has anybody ever noticed any digital reciprocity failure? my guess is: there is none?

Doyle Thomas · May 7, 2014

ralphlambrecht said:
Well,Itried it and you're right;I doesn't work,only HDR seems to work, but it was worth a try.while n the subject of reciprocity,has anybody ever noticed any digital reciprocity failure? my guess is: there is none?

digital reciprocity failure= noise the sensor is only "turned on" while the shutter is open. the current flowing thru the sensor creates heat and heat is the source of the noise. the high end surveillance equipment used by the military uses N2 cooling to reduce noise. the other thing they do is to use a technology that has been around since the 1960"s, liquid filled lenses. instead of there being a gap between the lens elements filled with nitrogen (cheap) or argon (better) the gap is filled with a refractive liquid that acts as an additional element. this is how they are able to read a license plate number from 200 miles up in space. don't tell anyone , its a secret!

liquid filled lenses have made their way into the semiconductor industry making it possible to create ever higher microchip density but has yet to make it to Photography.

toyotadesigner · May 8, 2014

Some stuff from the film era can't be reproduced with digital. There is no latency in a sensor - how should a sensor store photons until you press the shutter the second time?

indigo · May 8, 2014

jens g.r. benthien said:
Some stuff from the film era can't be reproduced with digital. There is no latency in a sensor - how should a sensor store photons until you press the shutter the second time?

The protons charges the photosite and causes it to raise the voltage until it is reset. So multiple exposures is possible with digital. Even with no light the voltage also rises but it's noise. That is why digitals have problem with noise in long exposure.

Highlandpete · May 9, 2014

ralphlambrecht said:
with film, shadow detail could be increased by giving the film a weaker pre exposure prior to the image exposure.does this technique work with digital sensors too?

Isn't that what Sony's DRO (D-Range Optimizer) function does? It increases shadow detail without blowing out the highlites.

toyotadesigner · May 9, 2014

The protons charges the photosite and causes it to raise the voltage until it is reset. So multiple exposures is possible with digital.

The photosite/sensor is reset in the very moment you release the shutter. Multiple exposures are calculated in-camera with a software, which superimposes the n images.

RalphLambrecht · May 9, 2014

thanks for aall the posts;I'm a bit smarter now but Iwouldn't mind links to more technical publications on the subject of digital reciprocity and latency if you have them.thanks

RalphLambrecht · Aug 27, 2016

Hatchetman said:
Yes, take two exposures and merge them somehow. Tone mapping? I don't know HOW to do it, I just know it can be done.

Actually,You can do it with a single exposure!
Just duplicate the layer in PS and select the blending mode'multiply'.the shadow detail is amazing but highlights ma have to be masked off not to burn out.But that all does not answer my original question, which is:"Does a sensor element get more sensitive with a light pre exposure just like film does?

ann · Aug 27, 2016

Digital doesn't require an adjustment for reciprocity failure

RalphLambrecht · Aug 28, 2016

Indigo said:
Ralph,
I don't think digital sensor has the toe like film so I don't think it would work.

actually digital has a very similarly-shaped S curve but it stilldoesn't work for other reasons as I recently found out

RalphLambrecht · Aug 28, 2016

ralphlambrecht said:
my Nikon D800 has a multiexposure function.so,I'll try it.I'm hoping it could improve the signal/noise thresholdand improve or decrease shadow noise.it's worth a try

improving signal to noise ratio is an interesting idea;must give that a try too

RalphLambrecht · Sep 3, 2017

RalphLambrecht said:
Well,Itried it and you're right;I doesn't work,only HDR seems to work, but it was worth a try.while n the subject of reciprocity,has anybody ever noticed any digital reciprocity failure? my guess is: there is none?

correction: HDR worked but exposure blending in PS worked even better.

Prof_Pixel · Sep 3, 2017

RalphLambrecht said:
actually digital has a very similarly-shaped S curve ...

I know the original posting is a year old, but unlike film, digital capture has a linear response; the S shaped image curve is a result of camera firmware or external software RAW conversion.

Eric Rose · Sep 3, 2017

I use a custom curves profile in my digi cam. +5 for shadows and -5 for highlights. The images come out REALLY great.

Bob Carnie · Sep 4, 2017

Ralph I use a flash in PS to tame clipped highlights in sky .. rather than have blank white.

Simple workflow

Make a layer- go to levels- under the histogram there is a bar where if you drag from the right you can introduce grey or tone into the image, (this flattens the overall scene) - then option click to get a black mask -- pick up a brush and paint in the grey into the clipped areas.. - adjust the opacity of the layer to your taste and flatten-- I use this technique quite a bit and it works for me.

Bob

BrianVS · Sep 4, 2017

I've found the easiest way to reduce noise is to use a lower contrast lens with veiling flare. This essentially gives an offset intensity to the sensor that gets it above the noise floor. Does anyone remember the modifications to the Nikon F to add small lamps that flashed as the exposure was being made? Kind of the same idea: add an offset to get the film past the threshold intensity for recording an image.

Digital sensors are for most of the usable exposure Linear Response. It is only at the extremes that a non-linear effect cuts in.

I wrote my own Raw Processor for the Leica M Monochrom to convert 14-bit sensor values to 16-bits using a curve.

Dead Link Removed

Written in FORTRAN, batch processes files.

digital pre-exposure

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