Digitally change f-number exposure is possible?

Short answer: No.

Long answer:

You can digitally decrease the exposure but if any channel is blown you're out of luck. Use RAW for a little more leeway.

Rodrigo Ayres Bordin said:

Hi!

Maybe it´s an stupid question... but here it goes...

I´m a dentist and often I take pictures of my clinical cases...

In situations of dental bleaching, I often set the same aperture, exposure, etc... to keep my pictures standartized (does this word exist?) to check colors changes in the teeth. But sometimes I forget and use another aperture. I just realize this aftewards, when my client is not at the office anymore... So my pictures sometimes are much brighter.

I´m not concerned at DOF, but mostly at color changes (lower apertures -> pictures are brighter, vice-versa)

So, is there any .. photoshop tool or something else in where I could correct the F-number and it automatically corrects the exposure to another f-number, with consistency? Rather than manually working through brightness controls?

Does something like this exist? Thanks!

Ps. I´ve got a Canon T2I with a Canon ring flash and a Canon Macro-100

Click to expand...

Yes there are two somethings which come close to what you want depending on whether you shoot RAW or jpeg.

If you shoot RAW and process using Adobe Camera Raw (Photoshop's RAW converter) then there is an exposure slider on the Basic tab. Increasing this by one unit increases the exposure by one stop. Therefore if you know the f-stop you took the image at and your standardised (or standardized, if you insist on using the spelling from across the pond) f-stop you can calculate what value to add (or subtract) to get your standard exposure. You can usually get away with +/-3 to 4 without too much damage to the image.

If you shoot Jpeg there is the exposure adjustment layer which provides a similar adjustment slider however due to the significantly lower amount of data available in a Jpeg you will see noticeable degradation in the image if you go beyond an adjustment of+/- 2.

Neither is ideal (much better to get it right in the camera in the first place) but should allow you some adjustment.

Hope this helps

Ian

Your problem is related to the issue of image-management. What you should have is a procedure to apply parameters to your RAW files, including the desirable White Balance, and make any exposure changes before exporting to a JPEG file. You will still need to tell the computer what is the correct exposure for each image, but that should be easy. Unless you're dealing with many thousands of images, making a script for automation is not worth the cost, especially since there will still be some variation in exposure depending on the position of the camera and the reflectance of the objects being photographed. Note that an exposure adjustment is not the same as a "brightness" adjustment.

Rodrigo Ayres Bordin said:

I´m a dentist and often I take pictures of my clinical cases...

In situations of dental bleaching, I often set the same aperture, exposure, etc... to keep my pictures standardised (does this word exist?) to check colors changes in the teeth. But sometimes I forget and use another aperture. I just realize this afterwards, when my client is not at the office anymore... So my pictures sometimes are much brighter.

Click to expand...

Yes, that's a word, and you need to do it.

I suggest that you use a colour chart to standardise your images, both for white balance and "tooth whitening". I don't know if there's a standard gradient chart for tooth whiteness, but that's what I mean. Hold it near the patient's mouth as you take the shot.

Google "Tooth Whitening Scale".

It's far better if you can get the exposure correct, but there are software adjustments. There's also "bracketing" (taking a series of shots of varying exposure).

Either way, I think that you need standardisation. Can you view the shots on the camera LCD to confirm that the exposure is OK?

I am not super knowledgeable about this, but many cameras allow you to set custom settings to a dial, so it should be possible to set it so that a certain dial position always gives you particular settings. Maybe someone else can give a better answer.

Andersonm said:

I am not super knowledgeable about this, but many cameras allow you to set custom settings to a dial, so it should be possible to set it so that a certain dial position always gives you particular settings. Maybe someone else can give a better answer.

Click to expand...

Very good solution. Set custom setting to a dial or button, whichever is available. Should work.

Sky

Rodrigo Ayres Bordin said:

Hi!

Maybe it´s an stupid question... but here it goes...

I´m a dentist and often I take pictures of my clinical cases...

In situations of dental bleaching, I often set the same aperture, exposure, etc... to keep my pictures standartized (does this word exist?) to check colors changes in the teeth. But sometimes I forget and use another aperture. I just realize this aftewards, when my client is not at the office anymore... So my pictures sometimes are much brighter.

I´m not concerned at DOF, but mostly at color changes (lower apertures -> pictures are brighter, vice-versa)

So, is there any .. photoshop tool or something else in where I could correct the F-number and it automatically corrects the exposure to another f-number, with consistency? Rather than manually working through brightness controls?

Does something like this exist? Thanks!

Ps. I´ve got a Canon T2I with a Canon ring flash and a Canon Macro-100

Click to expand...

The only camera which would allow you to do this is a plenoptic camera, such as a Lytro. Lytro has just quit the consumer market and you cna by remaindered stocks pretty cheaply. I'm not sure the ability to change lots of things (point of focus, DOF, etc) in post is necessarily a good payback for what you lose with respect to a more general purpose camera.

Everybody is still missing the point.

It's no good fiddling with the image after the event, no matter how clever that may seem.

Shoot the patient alongside a standard chart and it hardly matters what the exposure happens to be, although correct exposure would help.

It used to be standard practice to shoot biological specimens and soil samples including a reference color chart.

bobn2 said:

Rodrigo Ayres Bordin said:

Hi!

Maybe it´s an stupid question... but here it goes...

I´m a dentist and often I take pictures of my clinical cases...

In situations of dental bleaching, I often set the same aperture, exposure, etc... to keep my pictures standartized (does this word exist?) to check colors changes in the teeth. But sometimes I forget and use another aperture. I just realize this aftewards, when my client is not at the office anymore... So my pictures sometimes are much brighter.

I´m not concerned at DOF, but mostly at color changes (lower apertures -> pictures are brighter, vice-versa)

So, is there any .. photoshop tool or something else in where I could correct the F-number and it automatically corrects the exposure to another f-number, with consistency? Rather than manually working through brightness controls?

Does something like this exist? Thanks!

Ps. I´ve got a Canon T2I with a Canon ring flash and a Canon Macro-100

Click to expand...

The only camera which would allow you to do this is a plenoptic camera, such as a Lytro. Lytro has just quit the consumer market and you cna by remaindered stocks pretty cheaply. I'm not sure the ability to change lots of things (point of focus, DOF, etc) in post is necessarily a good payback for what you lose with respect to a more general purpose camera.

Click to expand...

I just reread your post and can give you a more sensible answer. I was misled by your headline about wanting to change f-number (or exposure) after exposure, both of which are impossible with a normal camera (though as I said above, the effects of a wider aperture can be had after exposure with a plenoptic camera). Now I realise that you just want to normalise the brightness range of your images.

You could do something with Image Magick (http://www.imagemagick.org/script/index.php)

In particular the normalize command (http://www.imagemagick.org/Usage/color_mods/#normalize) or maybe one of the other image adjustments.

IM is a command line tool, so you need too find a command that works, or write a little scrip (or borrow someone else's - there are lots of IM scripts around) but once you've done that, you can normalise a whole folder full of files in one go.

Rodrigo Ayres Bordin said:

Hi!

Maybe it´s an stupid question... but here it goes...

I´m a dentist and often I take pictures of my clinical cases...

In situations of dental bleaching, I often set the same aperture, exposure, etc... to keep my pictures standartized (does this word exist?) to check colors changes in the teeth.

Click to expand...

That is a good word, but it's spelled "standardised" [in the UK] or "standardize" in the USA. ;-) It's also the crux of the issue.

Rodrigo Ayres Bordin said:

But sometimes I forget and use another aperture. I just realize this aftewards, when my client is not at the office anymore... So my pictures sometimes are much brighter.

I´m not concerned at DOF, but mostly at color changes (lower apertures -> pictures are brighter, vice-versa)

So, is there any .. photoshop tool or something else in where I could correct the F-number and it automatically corrects the exposure to another f-number, with consistency? Rather than manually working through brightness controls?

Does something like this exist? Thanks!

Ps. I´ve got a Canon T2I with a Canon ring flash and a Canon Macro-100

Click to expand...

Good setup!

You can't change the aperture after the picture is made. But you can change the "brightness". Several people told you how. It's perhaps stupid, but Adobe and others call the control that affects "brightness", "exposure"! Just understand that this is just a dumb mistake; those controls really affect brightness.

If your whites are not blown, you can sorta recover a JPEG image that is overexposed. As many said, you should seriously consider saving RAW files! They allow much more latitude in changing things.

Wry Cuda hit the "nail on the head"; what you need [badly] is PROCESS CONTROL!

At a minimum, you need a white reference [grey card]. Take a picture of the grey card immediately prior to the "official" shot. Then in post, make that grey card:

• The correct brightness
• Have equal brightnesses of each of the colors

Almost any RAW Editor will have simple tools to do those two things.

There are many variations of a multi-color card, but I don't think that is necessary for your application. A strip w/ several shades of grey would be good?

To eliminate variability in camera settings, takes discipline. Make a check-list of all the camera settings to be certain they are all correct. "Don't try to takeoff w/ the flaps up!"

Everyone seems to be jumping in with complicated solutions. The OP usually gets his photos right - he sometimes forgets to set as he meant so the exposure/brightness comes out wrong. He no doubt can use a slider to reduce the brightness to that as if he had used the aperture he meant to. He wants to know if he can do this automatically so he has a valid comparison with the earlier ones taken at the correct setting. I believe the term is "normalise" but then that assumes the correct images he has are already normalised.

Personally I'd worry about going to a dentist that can't stick to procedures. But then again I might also worry about a photographer who wants to treat my teeth.

Anyhow well done BobN2 on reading the issue as I understand it albeit at the second attempt.

The free GIMP has a normalise process but how well this would work is another matter.

On the assumption that he has set the camera in manual mode, or a different metering mode, and ended up with using f/5.6 instead of f/8 - then can he automate changing the image so the brightness looks as if shot with f/8?

My reading of the problem is that both sets of photos are alright but they are not comparable with brightness adjustment.

This will take a bit of math to figure out, but yes. Brightness for a given sources correlate with the square of the F number and log 2 of the slider in the raw editor. So if you took pictures at F5.6 that were supposed to be F8, you'd take (8/5.6)^2, then figure out what this is as a power of two and adjust the slider accordingly. In this case, you would adjust -1 as you did double brightness.

This is assuming everything else is standardized. If you aren't familiar with the equipment, this may not be the case. You'd need a fixed EV and white balance for these photos to give meaningful data.

AnthonyL said:

Everyone seems to be jumping in with complicated solutions. The OP usually gets his photos right - he sometimes forgets to set as he meant so the exposure/brightness comes out wrong. He no doubt can use a slider to reduce the brightness to that as if he had used the aperture he meant to. He wants to know if he can do this automatically so he has a valid comparison with the earlier ones taken at the correct setting. I believe the term is "normalise" but then that assumes the correct images he has are already normalised.

Personally I'd worry about going to a dentist that can't stick to procedures. But then again I might also worry about a photographer who wants to treat my teeth.

Anyhow well done BobN2 on reading the issue as I understand it albeit at the second attempt.

The free GIMP has a normalise process but how well this would work is another matter.

On the assumption that he has set the camera in manual mode, or a different metering mode, and ended up with using f/5.6 instead of f/8 - then can he automate changing the image so the brightness looks as if shot with f/8?

My reading of the problem is that both sets of photos are alright but they are not comparable with brightness adjustment.

Click to expand...

That´s it! It always ok for my uses. I have some settings for pictures taken with a mirror inside the mouth, for instance, and it needs more light, so I increase the aperture (reduce the f-number). Sometimes I forget to set it back to the previous aperture. I always correct it at the moment, but there are times I´m a rush and I don´t...

I use the brightness settings in photoshop, but not always all the colors are adjusted the same way.. so it´s not easy and simple.. But I´m a photoshop newbie yet.

Flash is always manual, so I have to measure the distance from the face, teeth, and the lens, for instance, usually with my hand as a ruler to get similar results also... A minor change in distance changes the exposure also...

Thanks for all the answers!

Rodrigo Ayres Bordin said:

Flash is always manual, so I have to measure the distance from the face, teeth, and the lens, for instance, usually with my hand as a ruler to get similar results also... A minor change in distance changes the exposure also...

Click to expand...

I'm not sure if your T2i can do this...because I'm not a Canon user and don't follow everything Canon closely.

I think Canon adopted the Nikon CLS system several years ago. They call it something else, of course. What it does is the automate the flash system, so that you don't have to manually control it. It becomes the 4th parameter in the Brightness Pyramid:





Check and see if the equipment you have can be used automatically.

It's like magic until somebody explains how it works:

• The flash [or flashes] are told to emit a very short pulse of light
• The body sees that light pulse and determines how much light is needed
• The flash then delivers the length of light pulse that will make the scene the "correct" brightness
• All these pulses happen VERY fast and nobody knows what is going on

Once you get the camera set properly, you can just take pictures.

Re, you need to occasionally get more light down inside a mouth, save RAW and use an editor to simply brighten the shadows. It works great!

Rodrigo Ayres Bordin said:

Thanks for all the answers!

Click to expand...

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iancrowe said:

... If you shoot RAW and process using Adobe Camera Raw (Photoshop's RAW converter) then there is an exposure slider on the Basic tab. Increasing this by one unit increases the exposure by one stop.

Click to expand...

Well, not really. It changes the image's brightness by one stop. In this regard it is perhaps more analogous to changing ISO than exposure. OTOH, depending on how it handles the way the tone curve tails off at each end, it might seem more like a simulation of exposure adjustment than of ISO adjustment.

The exposure is the amount of light the image was captured with, and the software cannot go back in time and change that.

chuxter said:

Re, you need to occasionally get more light down inside a mouth, save RAW and use an editor to simply brighten the shadows. It works great!

Click to expand...

Not so great on Canon sensors. Even a 1 stop underexposure can be fatal (I experienced it from my friends with Canon gear).

baloo_buc said:

chuxter said:

Re, you need to occasionally get more light down inside a mouth, save RAW and use an editor to simply brighten the shadows. It works great!

Click to expand...

Not so great on Canon sensors. Even a 1 stop underexposure can be fatal (I experienced it from my friends with Canon gear).

Click to expand...

I forget. Been spoiled by the Sony sensors in Nikon cameras ability to drag up shadow detail.