Raw, Red filters & WB...oh my!

[cpanddp]

I understand shooting RAW gives me ability to make any necessary adjustments to image in software later but I'm a bit confused about something.

Do I need to use a red filter when shooting RAW? Why and if so under what conditions / depths.

or

Can I shoot RAW and just white balance the scene at depth (white slate) whithout need of a red filter.

or

??????

Guess what I am asking is what is going to produce best and most accurate results
RAW only...edit
RAW & red filter....edit
RAW & manual white balance at depth...edit
RAW, red filter & manual white balance at depth...edit
or other??

[Gilligan]

RAW = no filter required.

RAW = no white balance calibration required while diving.

RAW = doesn't matter much what white balance setting you use to shoot since you adjust it in post-processing. I use the "underwater" WB setting for non-strobe shots and the "auto" one for strobe shots just because you have to pick one.

HERE (http://jimspears.net/camera/dpp/white_balance/index.htm) is a sample of adjusting WB on RAW files with the Canon software.

For non-strobe shots = RAW. JPEG will not suffice.

For strobe shots = RAW. JPEG will suffice.

For best results on all shots all the time = RAW.

[spoolin01]

Is there a downside to shooting RAW with a red filter? Would it create a more balanced RAW image to work with from the start?

[Gilligan]

Is there a downside to shooting RAW with a red filter? Would it create a more balanced RAW image to work with from the start?

It will not create a more balanced RAW image. There is no advantage to using a red filter when shooting RAW. The downside IMO is you are carrying an extra piece of equipment that you don't need.

[spoolin01]

If the water is filtering out one region of the spectrum, optically shouldn't you be able to compensate with additional filters, so that the end result is like a neutral density filter? Just as a matter of simple spectroscopy. If that's not a better starting point for software-based processing, I'm interested to understand a little of why that is. Assuming overall exposure isn't limiting, it's not better to start with more natural relative levels of the primary colors? The sensors must have working ranges, isn't it better to not feed them lots of blue relative to red, assuming that you can feed them enough of each once they're back in better balance?

[Jak Crow]

If you're using RAW, you don't need to bother with any filters. You can fix everything post-process.

[spoolin01]

Why not fix it pre-process? Is there really no difference? Why is it better (or indifferent) to start with an image that's all blue?

(Livermore was my home town!)

[beautybelow]

One good reason not to use a red filter is it cuts out light.

Another is that sometimes you may not need all of the "correction" that the red filter applies. For instance if you are shooting up and have a lot of sun lit area in the image you may not get the desired effect throughout the entire image.

[Gilligan]

Why not fix it pre-process? Is there really no difference? Why is it better (or indifferent) to start with an image that's all blue?

(Livermore was my home town!)

Non-strobe shots:
>You can't fix a JPEG shot pre-process other than by calibrating your white balance off a slate or the like and at varying depths and ambient light conditions. It yields the best results for shooting JPEG and requires the most work underwater. I did it for years until I bought my G10 with RAW and even then it took awhile to convert me.
>You get blue photos if you shoot JPEG in the "auto" white balance setting.
>You get better shots if you shoot JPEG in the "underwater" versus "auto" white balance setting if the camera has it. And that setting diminishes in quality as you get deeper.
>You get the best results by shooting RAW then using the eyedropper tool in the post-processing software. JPEG pales in comparison.
As "beautybelow" stated a red filter reduces the amount of light. Red filters went out the window when RAW was born.

Strobe shots:
>You don't need a red filter if you are using an on-board strobe or an external strobe as the strobe supplies the light.
>If you shoot JPEG and calibrate your white balance for a non-strobe then forget to switch it back to "auto" for a strobe shot you get a red photo and it's toast.

When you post-process a RAW file you can save the changes you made to it and if you change your mind when you open it again you can revert back to the original shot.

>JPEG's can yield good results when using a strobe and the camera in Manual or Tv or Av mode.
>JPEG's can't touch RAW for non-strobe shots.

[mjh]

I understand the comments about fixing everything in RAW but recall a review of the D7000 done on Wetpixel where I think for video they did use a filter.

[beautybelow]

I would use a filter for video too but I didn't think he was asking/debating about video.

[spoolin01]

I'm just coming at this from the simple spectroscopy/histogram side, and I don't know much about camera physics or post-processing. I appreciate the comments and indulgence while I try to understand this.

The water is a blue filter that cuts out red light, so you take the red light that you let in through the lens and differentially amplify it with software. You've let in less red light than you possibly could, because if you let in more red, you'd have too much blue. You have to make that trade-off because the exposure settings can't differentiate red from blue, and there's no option on the hardware side (except for filters) to do that either - no red ISO vs blue ISO.

So you've got a low intensity image (the red one) that you bump up with software - that increases the noise, because detectors have sensitivity threshholds, and you've underexposed the red ones.

If on the other hand, you choose to filter the blue light similarly to what the water has done to the red, such that the incident light histogram is now (largely) restored to above-water spectral distribution, then increase the exposure to restore intensity lost to the additional filtering - now your red and blue detectors are getting more balanced input. Other considerations aside (depth of field from opening the iris, say), the detectors don't know what machinations created their light, just that the spectral distribution is better red-blue balanced, and that overall exposure is correct.

Given the noise issue (using that term broadly to mean the quality of the data), how can than not be a better starting point, that's the part I haven't yet gotten. I don't think it matters whether the [-]blue[/-] redfilter exactly complements the red filtration done by the water - it only matters which incident histogram more closely matches what you want (since software will do the rest), and whether that makes for a better image in the end.

[spoolin01]

One good reason not to use a red filter is it cuts out light.

Another is that sometimes you may not need all of the "correction" that the red filter applies. For instance if you are shooting up and have a lot of sun lit area in the image you may not get the desired effect throughout the entire image.If you're too shallow or the incident light is spectrally balanced, like using a strobe and red filter at the same time, the filter reduces the balance rather than making it better, I've seen that happen a lot with shallow water video.

[beautybelow]

Do you just want to debate the physics of using a filter or do you want to figure out the practicality of using a filter in still photography underwater?

You lost me on the water is blue...

What kind of camera are you talking about using? If it is one you can slip a wet filter over the lens port then go for it. If you like it yippee and if you don't, take it off.

If you are talking about using a threaded filter on the end of your lens then I would feel too restricted, not being able to take it off during the dive.

[under water]

I am of the opinion that MY videos are optimized when I use a red filter. I have however seen some wonderfully balanced videos that apparently only relied on proper White Balance.
OK. I realize that was about video, not stills.

If I am shooting stills as well and cannot remove the red filter, I will use RAW and the same argument that says "you don't need a filter" lets you adjust the red out in post processing.

From a densitometric perspective, it does make sense that you can get a better image if you use a red filter, White balance and RAW together for ambient light pix. If you can minimize the delta between the sensors and get to a more neutral area via a red filter, then you are not going to need to boost red (actually attenuate blue & green)as much in post processing (whether on the PC or in the camera).
It is important that you white balance if you are using a red filter if you are saving JPEGs. You can adjust RAW later, but I think it is way better to optimize during shooting so that your JPEG is reasonable. If you don't save JPEGs then you don't need to White Balance.

In practice though, most use a strobe that is close to daylight and the foreground will come out too red if you use a strobe and a red filter, unless you white balance for the combo (again, WB only useful for JPEGs).

Some folks have used blue filters on their strobes and red filters to try and balance everything, but that is a pain and I doubt many folks do it.

An example of a strobe picture and a red filter (using RAW)
http://www.delargy.com/share/original-with-filter-and-strobe-no-cc.jpg

After color balance in Lightroom.
http://www.delargy.com/share/with-color-correction-with-filter-and-strobe.jpg

Another thread that discussed this topic
http://www.scubaboard.com/forums/tips-techniques/366567-red-filters.html

[Gilligan]

I understand the comments about fixing everything in RAW but recall a review of the D7000 done on Wetpixel where I think for video they did use a filter.

You are correct, there is still a place for red filters using video but I didn't want to inject that into this discussion as it was about still photos.

[spoolin01]

Do you just want to debate the physics of using a filter or do you want to figure out the practicality of using a filter in still photography underwater?

You lost me on the water is blue... you might be referring to the analogy I was making of water to a 'blue filter'. Blue filter + red filter ~= neutral density filter, was the simple thinking

What kind of camera are you talking about using? If it is one you can slip a wet filter over the lens port then go for it. If you like it yippee and if you don't, take it off.

If you are talking about using a threaded filter on the end of your lens then I would feel too restricted, not being able to take it off during the dive.I wasn't thinking about filters inside the housing, just the point and shoot type where the filter is on the wet side. I'm interested in the physics, optics, sensor-response, and post-production of underwater stills, looking for a technical explanation of why those would all work better jointly - image quality-wise - w/o use of filters, when it seems the raw material would start out in better balance with use of a red filter. If it's just a matter of convenience, I can see that. But I'd also like to understand the quality effect.

[spoolin01]

Here's a discussion of filters and UW photo I googled up.

Filters and Ambient Light Photography :: Wetpixel.com (http://wetpixel.com/i.php/full/filters-and-ambient-light-photography/)

under water - you and the wet pixel guys mention white balance. Does that mean you're
a- shooting jpeg
b- talking about white balancing during post-processing (do you use the grey card in that way also?)
c- referring to some use of white balance in the context of RAW that I haven't heard about

[under water]

Here's a discussion of filters and UW photo I googled up.

Filters and Ambient Light Photography :: Wetpixel.com (http://wetpixel.com/i.php/full/filters-and-ambient-light-photography/)

under water - you and the wet pixel guys mention white balance. Does that mean you're
a- shooting jpeg
b- talking about white balancing during post-processing (do you use the grey card in that way also?)
c- referring to some use of white balance in the context of RAW that I haven't heard about
a. White Balance while shooting is needed if you shoot JPEG combined with RAW or just JPEG, OR (especially) if you are shooting video.

b. Post processing color balance using the dropper to adjust the color is also referred to as White Balance and is what you do to balance those RAW pictures. Usually it is a first step, sometime combined with sharpening and other changes to the curves.

c. No need to use WB while shooting RAW only. It doesn't change what the sensor gets and stores, just how it processes it for JPEGs. Which is why a filter can be useful for ambient conditions for the reasons stated before.

[Gilligan]

I wasn't thinking about filters inside the housing, just the point and shoot type where the filter is on the wet side. I'm interested in the physics, optics, sensor-response, and post-production of underwater stills, looking for a technical explanation of why those would all work better jointly - image quality-wise - w/o use of filters, when it seems the raw material would start out in better balance with use of a red filter. If it's just a matter of convenience, I can see that. But I'd also like to understand the quality effect.

I guess the only way to know for sure is to take photos at varying depths with and without a red filter in RAW mode for comparison. I would gladly do it but I don't have a red filter anymore.

[spoolin01]

I can try this next time I'm in Hawaii, but I don't think my eye is discriminating enough to know how to see a difference that might be there, but subtle.

[under water]

I can try this next time I'm in Hawaii, but I don't think my eye is discriminating enough to know how to see a difference that might be there, but subtle.

That would be a great test. Look for a differences in grain in the darker parts of the picture. I would be curious to see if the addition of a filter causes the sensors to work harder (less light) or if the more neutral balance allows for less dramatic changes in post processing of the RAW files.

[Viz'art]

I differ on that point profoundly, Color correction filter are a very usefull tool and would recommend reading the following before claiming they went out the windows when RAW showed up, M A G I C - F I L T E R S (http://www.magic-filters.com/need.html)

If you remove red from the environment you are shooting in, then the camera will try to compensate by pushing the blue and green into submission, adding the filter rebalances the color environment of the scene so that the color space of your camera has a healthier file to work with. it does make a big difference when you start enlarging the image or submitting them for publications.

[Gilligan]

I differ on that point profoundly, Color correction filter are a very usefull tool and would recommend reading the following before claiming they went out the windows when RAW showed up, M A G I C - F I L T E R S (http://www.magic-filters.com/need.html)

If you remove red from the environment you are shooting in, then the camera will try to compensate by pushing the blue and green into submission, adding the filter rebalances the color environment of the scene so that the color space of your camera has a healthier file to work with. it does make a big difference when you start enlarging the image or submitting them for publications.

The Magic Filter examples shown on the site are all JPEG photos indicating the comparison between using the Magic Filter and not using it. There are no comparisons of using the filter with RAW.

The only RAW comparison on that site is the difference between Auto and Manual WB to indicate the amount of digital noise. I'm not sure what they mean by "manual" white balance? When you shoot RAW you don't calibrate your WB pre-shot? There are no examples there that I can see with and without a filter shooting RAW.

I would still need to see a RAW shot with and without a red filter to convince me the filter makes an improvement when shooting RAW on non-strobe shots.

[jdandvalerie]

The Magic Filter examples shown on the site are all JPEG photos indicating the comparison between using the Magic Filter and not using it. There are no comparisons of using the filter with RAW.

The only RAW comparison on that site is the difference between Auto and Manual WB to indicate the amount of digital noise. I'm not sure what they mean by "manual" white balance? When you shoot RAW you don't calibrate your WB pre-shot? There are no examples there that I can see with and without a filter shooting RAW.

I would still need to see a RAW shot with and without a red filter to convince me the filter makes an improvement when shooting RAW on non-strobe shots.

Just throwing in my 2 cents. I do not think the red filters are necessary when shooting RAW. That being said, when shooting raw I still manually set my WB using a white card. My reason for this is for video. I shoot with a Canon 7d and always use a custom WB, if I am "strobe-less". When I take stills, I'm still using a custom WB carried over from my video setting unless of course I have my strobes in which I will change to AWB for stills.

Evin if I'm shooting Raw with Custom WB, when I'm processing the stills, I'll still tweak the WB.

My opinion is based on personal preference and quality of work when it's all said and done, but I haven't used red filters in over 5 years. As soon as I was able to shoot RAW (and subsequently shoot video with a custom WB) there was no need for a filter.

As Giligan said above, a post editing comparison of a few shots would be the only way for you to settle this for yourself. But all the literature I have read indicates that RAW=no filter needed/no custom WB for stills as it is unncessary.