Do optical WB filters improve RAW color latititude?

Started Aug 26, 2012 | Discussions
Vitruvius Junior Member • Posts: 43
Do optical WB filters improve RAW color latititude?

I know this might get really technical, but I am wondering if an optical color correction filter can enhance a digital RAW file. I know the RAW file is “what the camera sees” without correction. So you can shoot RAW and then you allow the camera to adjust White Balance or you do it yourself later on the computer. The question really is; do you lose more image color information by shifting the post exposure digital image later or by filtering the incoming light with an optical color filter during exposure? I have FL-D and blue filters for incandescent light from the film days. I guess I should do some trials but I wouldn’t know where to start with the technical comparisons.

I am thinking that digital RAW files would have more color latitude if they were pre-white-balanced during exposure by a color correction filter. Not sure though. Thanks in anvance.

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sherwoodpete
sherwoodpete Veteran Member • Posts: 7,766
Re: Do optical WB filters improve RAW color latititude?

http://forums.dpreview.com/forums/read.asp?forum=1018&message=29592761
Quote: ' Two - The 80A "Color Balancing" Filter '

OP Vitruvius Junior Member • Posts: 43
Re: Do optical WB filters improve RAW color latititude?

That is what I was suspecting, thanks for the link. very interesting and makes total sense. I just don't know why digital photogs these days don't use filters then.

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Mako2011
Mako2011 Forum Pro • Posts: 23,423
Note...no need

Vitruvius wrote:

That is what I was suspecting, thanks for the link. very interesting and makes total sense. I just don't know why digital photogs these days don't use filters then.

I would note that the linked thread also points to the luminous-landscape articles on the subject. With the exception of a ND filter and POL filters.

" .....color that was saturated using PhotoShop, is cleaner with more pleasing colours than the enhancement filtered but magenta-corrected one on the right. My take therefore is that the use of a colour enhancing filter is largely redundant if you will be processing your images digitally prior to output. Even if you are using traditional printing means then you will have to correct for a major magenta imbalance that seriously compromises the benefits of the filter to begin with."

With the abilities of CS6 and associated 3rd party plugins....I reall see no need for color filters any longer.

" ....that a colour enhancing filter is essentially redundant if you use digital image processing techniques. Simply put, whatever these filters can do can be done better in PhotoShop.

That really seems to be the case when doing side by side comparisons with current gen software.

John Sheehy Forum Pro • Posts: 19,148
Re: Do optical WB filters improve RAW color latititude?

Vitruvius wrote:

I know this might get really technical, but I am wondering if an optical color correction filter can enhance a digital RAW file. I know the RAW file is “what the camera sees” without correction. So you can shoot RAW and then you allow the camera to adjust White Balance or you do it yourself later on the computer. The question really is; do you lose more image color information by shifting the post exposure digital image later or by filtering the incoming light with an optical color filter during exposure? I have FL-D and blue filters for incandescent light from the film days. I guess I should do some trials but I wouldn’t know where to start with the technical comparisons.

I am thinking that digital RAW files would have more color latitude if they were pre-white-balanced during exposure by a color correction filter. Not sure though. Thanks in anvance.

You can use optical color filters to get various effects, but for the two situations of which you speak - old-style flourescent and incandescent, filtration can be counter-productive, unless you are doing long exposures at base ISO. If you are using a high ISO because of a needed shutter speed, you will need an even higher ISO with the filter. So, if you use the blue filter for incandescent, you will create slightly more noise in the blue channel, and even more noise in the green and red channels which you will weaken further. If, however, you are shooting at base ISO on a tripod, then yes, you can reduce the noise in the blue channel by using the correction.

BTW, what you are suggesting filters the scene to be treated by daylight, which seems logical, but daylight is not the native WB of digital cameras! The vast majority of them create white in the RAW data when red is twice as strong as green, and blue is 1.4x as strong as green, IOW, the native WB is a pinkish-magenta. You will get a minimum of chromatic noise and a maximal DR of full-color when the lighting is magenta. When the lighting is greenish, you get the maximal DR with monochrome extended highlights and shadows, but minimal full-color DR.

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John

OP Vitruvius Junior Member • Posts: 43
Re: Do optical WB filters improve RAW color latititude?

So now I am getting oposing massages. One says, and I thought, that sensors are designed to "daylight' WB. Your post seems like you know your stuff too and I don't doubt that it may be true. But now I am more confused. Thanks though.

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OP Vitruvius Junior Member • Posts: 43
Re: Note...no need

Wouldn't any post exposure adjustment cause loss of some color information? So when you 'boost' a color you are 'stretching' it and the software needs to interpolate and fill in the gaps so then there would be a chance of color banding. Right?

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Mako2011
Mako2011 Forum Pro • Posts: 23,423
Nope

Vitruvius wrote:

Wouldn't any post exposure adjustment cause loss of some color information? So when you 'boost' a color you are 'stretching' it and the software needs to interpolate and fill in the gaps so then there would be a chance of color banding. Right?

No, Sensors and PP have come quite far.

http://www.luminous-landscape.com/tutorials/filters.shtml
http://www.luminous-landscape.com/reviews/comparison.shtml

Also note... advances by the likes of Topaz and Nik software really have made color enhancing filters less effective than doing it digitally

Olaf Ulrich Contributing Member • Posts: 953
Re: Do optical WB filters improve raw color latititude?

Vitruvius wrote:

I am wondering if an optical color correction filter can enhance a digital raw file.

Yes, they can.

.

Vitruvius wrote:

I know the raw file is “what the camera sees” without correction.

No, it isn't. That's an over-simplification and a common misconception ... but it's another topic altogether.

.

Vitruvius wrote:

I am thinking that digital raw files would have more color latitude if they were pre-white-balanced during exposure by a color correction filter. Not sure though.

Yes, that's correct. Using colour-correction filters to pre-balance the light colour in ligthing situations that are far off from daylight does increase dynamic range indeed. In typical tungsten light you will gain approx. one f-stop worth of dynamic range, or even more depending on the light, the filter, and the camera. Of course, this will come at the expense of a considerable loss of light, as these blue colour-correction filters are pretty dense. You'll lose about two or three stops of light. When shooting hand-held, this usually will force you to crank up the ISO setting in order to avoid camera shake. And the higher ISO setting then will offset the gain in dynamic range from the pre-balancing.

So using these 80A or KB12 or KB15 filters in dim tungsten light is useful only when you can shoot from a tripod at a low ISO setting and use slow shutter speeds without problems ... i. e. no hand-held shooting and no fast-moving subjects. When you need faster shutter speeds (and hence, higher ISO settings) then using those colour-correction filters will do more harm than good.

Olaf Ulrich Contributing Member • Posts: 953
Re: Do optical WB filters improve raw color latititude?

Oops, double post. Deleted.

alanr0 Senior Member • Posts: 1,888
Sensor CFA design, optical WB filters and RAW color latititude

Vitruvius wrote:

So now I am getting oposing massages. One says, and I thought, that sensors are designed to "daylight' WB. Your post seems like you know your stuff too and I don't doubt that it may be true. But now I am more confused. Thanks though.

If the sensor were designed so that red, green and blue channels saturated uniformly under 'daylight' illumination, then you would need to under-expose the green channel whenever the colour temperature shifted appreciably. The eye is most sensitive to green wavelengths (around 555 nm), so with less green light on the sensor, perceived image noise would be degraded.
http://en.wikipedia.org/wiki/Luminosity_function
http://en.wikipedia.org/wiki/Thermal_radiation

In practice, red and blue channels are made less sensitive than green.
For example: http://www.photo-lovers.org/pdf/kaf-10500longspec.pdf (page 14).

This means that for a useful range of illumination conditions, exposure depends strongly on the green channel, where the eye is most sensitive. Colour temperature can shift (within limits) without either red or blue channels clipping, provided the colour-weighted exposure is unchanged.

Rather than aggressively optimise performance for a single colour temperature, we for aim good performance with a much wider range of lighting conditions.

As John says, using a blue filter to re-balance tungsten illumination can improve signal to noise and colour accuracy in the shadows, provided you increase exposure time rather than pushing the ISO. For very long exposures (seconds and longer) you should also consider sensor leakage noise, which depends on the sensor design and degrades as operating temperatures rises.

HTH
--
Alan Robinson

Mako2011
Mako2011 Forum Pro • Posts: 23,423
Re: Do optical WB filters improve raw color latititude?

Olaf Ulrich wrote:

Vitruvius wrote:

I am wondering if an optical color correction filter can enhance a digital raw file.

Yes, they can.

Enhance compared to what? The same "enhancement" is now better done in PP. May note have been the case 4 years ago, but is now.

.

.

Vitruvius wrote:

I am thinking that digital raw files would have more color latitude if they were pre-white-balanced during exposure by a color correction filter. Not sure though.

Yes, that's correct. Using colour-correction filters to pre-balance the light colour in ligthing situations that are far off from daylight does increase dynamic range indeed. In typical tungsten light you will gain approx. one f-stop worth of dynamic range, or even more depending on the light, the filter, and the camera. Of course, this will come at the expense of a considerable loss of light, as these blue colour-correction filters are pretty dense. You'll lose about two or three stops of light. When shooting hand-held, this usually will force you to crank up the ISO setting in order to avoid camera shake. And the higher ISO setting then will offset the gain in dynamic range from the pre-balancing.

So using these 80A or KB12 or KB15 filters in dim tungsten light is useful only when you can shoot from a tripod at a low ISO setting and use slow shutter speeds without problems ... i. e. no hand-held shooting and no fast-moving subjects. When you need faster shutter speeds (and hence, higher ISO settings) then using those colour-correction filters will do more harm than good.

Well said

John Sheehy Forum Pro • Posts: 19,148
Re: Note...no need

Vitruvius wrote:

Wouldn't any post exposure adjustment cause loss of some color information? So when you 'boost' a color you are 'stretching' it and the software needs to interpolate and fill in the gaps so then there would be a chance of color banding. Right?

Posterization only occurs if software uses poor precision or works in an imprecise bit-depth, like 8-bit, on relatively noise-less areas of an image. You should not get any posterization in 16-bit editing.

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John

John Sheehy Forum Pro • Posts: 19,148
Re: Nope

Mako2011 wrote:

Also note... advances by the likes of Topaz and Nik software really have made color enhancing filters less effective than doing it digitally

Noise and DR can be improved with careful filtering of light - you can not replicate that in software. Relying on NR reduces detail; it's not the same thing.

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John

Barrie Davis
Barrie Davis Forum Pro • Posts: 21,460
Re: Do optical WB filters improve raw color latititude?

Mako2011 wrote:

Olaf Ulrich wrote:

Vitruvius wrote:

I am wondering if an optical color correction filter can enhance a digital raw file.

Yes, they can.

Enhance compared to what? The same "enhancement" is now better done in PP. May note have been the case 4 years ago, but is now.

.

.

Vitruvius wrote:

I am thinking that digital raw files would have more color latitude if they were pre-white-balanced during exposure by a color correction filter. Not sure though.

Yes, that's correct. Using colour-correction filters to pre-balance the light colour in ligthing situations that are far off from daylight does increase dynamic range indeed. In typical tungsten light you will gain approx. one f-stop worth of dynamic range, or even more depending on the light, the filter, and the camera. Of course, this will come at the expense of a considerable loss of light, as these blue colour-correction filters are pretty dense. You'll lose about two or three stops of light. When shooting hand-held, this usually will force you to crank up the ISO setting in order to avoid camera shake. And the higher ISO setting then will offset the gain in dynamic range from the pre-balancing.

So using these 80A or KB12 or KB15 filters in dim tungsten light is useful only when you can shoot from a tripod at a low ISO setting and use slow shutter speeds without problems ... i. e. no hand-held shooting and no fast-moving subjects. When you need faster shutter speeds (and hence, higher ISO settings) then using those colour-correction filters will do more harm than good.

Well said

It would seem, therefore, that for any one ISO it is a matter of either concentrating the noise in ONE channel (blue) when using no 80B in tungsten conditions...

... or spreading the noise more equally across all THREE channels by using an 80B to pre-balance the light to an assumed daylight sensitivity...[???]

Well, I did some tests a few years back (using Konica Minolta A2 camera, also Canon D20 dSLR) and found there was precious little difference, either way. I also tried it with the Panny LX3 rather more recently, and found it was even more of a waste of time... and light strength.

So that's all good then. Carry on.
--
Regards,
Baz

"Ahh... But the thing is, these guys were no ORDINARY time travellers!"

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Mako2011
Mako2011 Forum Pro • Posts: 23,423
Try it

John Sheehy wrote:

Mako2011 wrote:

Also note... advances by the likes of Topaz and Nik software really have made color enhancing filters less effective than doing it digitally

Noise and DR can be improved with careful filtering of light - you can not replicate that in software. Relying on NR reduces detail; it's not the same thing.

Actually you can do it much cleaner and better with Software digitally now than with optical filters. Read the article I linked then try it with today's products. It really is better to do it digitally..... except perhaps in very specific cases when long exposure at base ISO is possible.

Mako2011
Mako2011 Forum Pro • Posts: 23,423
correct

Barrie Davis wrote:

Well, I did some tests a few years back (using Konica Minolta A2 camera, also Canon D20 dSLR) and found there was precious little difference, either way. I also tried it with the Panny LX3 rather more recently, and found it was even more of a waste of time... and light strength.

That is correct. And in the last year with CS6 combined with 3rd party plugins...it now far more cleaner/optimal to do it digitally.

Franka T.L. Veteran Member • Posts: 8,143
Re: Do optical WB filters improve RAW color latititude?

well , I think you need to brush up on some of those using UNIWB and Color correcting CC filter. The concept is that the sensor ( usually ) are more sensitive on the G level since there are twice of them vs the B and R photosites, and by switching to a UNIWB and utilizing CC filter to cut down to G exposure enough to put it on par with the R and B then its possible not to burn the G before the R and B also ramp up to the limit thus better utilizing all the Color DR.

Of course physically specking the sensor is not gaining any more DR, but its one of the technique to gain better Color accuracy and Spectral tonal spread ( Color DR if you would ).

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  • Franka -

Olaf Ulrich Contributing Member • Posts: 953
Re: Do optical WB filters improve raw color latitude?

Franka T.L. wrote:

Well , I think you need to brush up on some of those using UNIWB and Color correcting CC filter. The concept is ...

This concept is something else. Just because one thing reminds you of another, it doesn't mean the two were the same. These are similar but still different topics.

John Sheehy Forum Pro • Posts: 19,148
Re: Try it

Mako2011 wrote:

Actually you can do it much cleaner and better with Software digitally now than with optical filters. Read the article I linked then try it with today's products. It really is better to do it digitally..... except perhaps in very specific cases when long exposure at base ISO is possible.

I already said that color filters can be counter-productive if they force a higher ISO.

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John

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