is there a role for color conversion filters in the digital age ?

[albertknappmd]

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Is there are role for the tried and true color conversion filters such as an 81B in the digital age or do we just use a straight Uv or in hte case of the M8, an UV/IR and follw up in RAW with Temp change and /or in Photoshop with filters ? I think that the digital age has claimed the life of this line of filters but want to hear other members thoughts...

Thanks as always,

Albert:rolleyes:

[Guest rubidium]

In general I would have to agree that, in practical shooting, these filters have essentially become moot with digital image capture and subsequent processing. Technically, however, it's possible to come up with an argument that differentiates between analog filtering and the color filtering that can be realized in digital processing. My argument is as follows ...

 

Each pixel in a sensor array is sensitive to a *broad bandwidth* of wavelengths corresponding to the respective class of pixel (red, green, or blue). Digital color filtering can only apply a single weight to each class, whereas analog filtering can provide much finer differentiation among wavelengths based upon the transmission vs wavelength profile of the design. Usually the latter is controlled by the mixture of dyes in a gelatin layer or by the mixture of compounds added to the glass melt, to the extent that there can generally be more than three degrees of freedom available to the designer depending on how complex that mixture is made to be. Thus, in principle, achieving similar levels of differentiation among wavelengths afforded by an analog filter would require a greater number of classes of more narrowband pixels, and hence more degrees of freedom made available to the digital processing.

 

At a practical level, does any of this matter? Given my experience with the DMR, it does not in my opinion.

 

Jim

[Guest guy_mancuso]

Albert not really from the camera point of view since you can WB almost anything to your taste. However with mixed lighting the light itself will look mixed so for intance your shooting in a factory with flouresents and a metz strobe and exposing for both like dragging the shutter , now if you WB balance for the strobes than the background will still have the flouresent green back there . Now if you want to balance the scene like we did with film we would use a slightly green filter on the flash than throw a 40 magenta on there but digital just put it on the flash and you get nice green images and than WB that and your nice even colored light across the whole scene now. This is probably the only time you may want to do this because green is well ugly to look at. The same is true with mixing strobe and tungsten and can put a warm filter on the flash to balance BUT most folks don't do that because the warm light is much nicer to look at in the background and many prefer that look like interiors for instance. So really from a practical level the green is the worst and maybe want to look at that in those kinds of situations otherwise the only filter really for camera is a polarizer and even than it can look overdone. Here in te Southwest with this bright sun and very blue skies the use of a Polarizer can look way overboard. I don't use them because the sky is blue enough.

[jaapv]

I would propose that if you have to filter any particular colour in your digital image you will be losing dynamic range in that colour. Normally that would probably not be enough to matter, but in extreme cases or when dr is fully used it may make a difference. Better to get it right on the sensor imo.

[nzav]

In a nutshell, yes, but with a caveat. Your sensor has only one ISO (referred to as "native") and one white balance at that native ISO (usually daylight for equal response from the R/G/B filters of the Bayer Array). Native is most often the lowest ISO (160 in many Kodak sensors) and any higher ISO settings require the signal voltages from the individual photosites to be electronically amplified.

 

This amplification, just like your stereo, will start to introduce distortion as you increase it; we call it noise. The higher the ISO setting, the more amplification and resulting noise you will experience. Here is where white balance issues arise in camera, or later in Photoshop. When you white balance the image for tungsten light for example, you are boosting the blue channel way out of proportion to the red and green channels. That is because tungsten light is deficient in blue, hence the blue tint of color conversion filters like 80A, 80B, 80C. By using one of these filters, you are equalizing the proportion of R/G/B light striking the sensor and making the incandescent light more like daylight.

 

The downside is this is accomplished by passing more blue light to the sensor while holding back some red and green. You are in essence losing the total amount of light which can be a problem for poor lighting situations. There is a fine line between the loss of quality due to raising the ISO or using longer shutter speeds to compensate for the light loss from the filter, and the inevitable noise in the shadows on your blue channel due to the required amplification to equalize the primary colors. Using color correction filters offers the ability to clean up the shadow noise if you have enough light to stay above slow shutter speeds that can induce other types of noise.

[albertknappmd]

A most thought provoking and erudite dicussion ! What a pleasure it has been reading the threads... From a theoretical point, it makes sense to keep and USE the color correctors but from a practical point, I will opt to correct with software... The glaring example would be the fluorescent lighting and this should be corrected with filters beforehand...

Again, the responses engendered by this question are all of the highest order and are most informative. :)

[Guest guy_mancuso]

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Yes , Nick thanks for that and was enlightening on the technical side of it, i was thinking more from the practical side of shooting. Both very good sides of the issue. Good thread i agree

[andit]

Hi Albert,

 

I switched to digital in the early days (Canon D60, which is still in use, albeit that I use only ISO100), and have always shot in the same way as I used to with E6 film. Since I generally do landscape photography, I make extensive use of a polarising filter and in 99% of the cases a 81A or 81B filter.

 

I'm going to expose my ignorance here, but up until now, I never actually thought of the fact that the filter would change the way the sensor sees the light... I must say that by metering the same as I would for slides, that is to meter for the highlights, I have never had any adverse effects in the photo's.

 

Also, when shooting B&W straight out of the camera, I still make use of Red and Yellow filters, again with much success. One benefit of using these filters, is that you cut down the amount of PS time, so I guess what I'm trying to say, IMHO, is that it is better to make your image as "perfect" as possible straight out of the camera...

 

I'm not a professional, and it makes a great deal of sense what other people have mentioned in this thread, but that is my 2 cents worth.

 

Andreas

[jaapv]

Andreas,

There are some very nice C1 profiles for B&W around, giving your about sixteen different digital yellow, red, green and blue filters for all your lenses with less to lug around - and pay for, without adding significantly to your post-processing time. PSE5 has a similar feature if you shoot Jpeg. And please post some photographs from your country. Africa is sorely missed in the various galleries on the internet forums.

[nemeng]

In a nutshell, yes you still need filters for high quality work.

 

See the general Wikipedia entry on Colour Temperature at:

 

Color temperature - Wikipedia, the free encyclopedia

 

... and scroll down the page to the "Spectral power distribution plot" heading. Have a look at the graphs and you'll see why you need to filter excess red+yellow frequencies from incandescent or fluorescent light sources.

 

See also the spectral distribution curves for various indoor lighting options at:

 

Learn About Light: Spectral Power Distribution Curves: GE Commercial Lighting Products

 

Hence using a blue (or magenta) filter to correct the colour as much as you can before it hits the film/chip. Not enough blue still equals not enough blue, and fiddling with the WB after the fact isn't going to change things :?)

[Guest magyarman]

I would propose that if you have to filter any particular colour in your digital image you will be losing dynamic range in that colour. Normally that would probably not be enough to matter, but in extreme cases or when dr is fully used it may make a difference. Better to get it right on the sensor imo.

 

Yesterday you tell is ok M8 need IR filters on front of lens becaus always we use filters for make correct light on film. Today you tell is better not use filter on digital becaus is not need by digital camera. This exactly what I tell from start, I sorry was too bat mine Englisch before you make understand.

[jaapv]

Yesterday you tell is ok M8 need IR filters on front of lens becaus always we use filters for make correct light on film. Today you tell is better not use filter on digital becaus is not need by digital camera. This exactly what I tell from start, I sorry was too bat mine Englisch before you make understand.

You're confused, Blasko, I was saying it IS better to use filters on a digital camera for colour correction here.

[andit]

Hi Jaap,

 

Thank you for your advice. I've got an M8 on order which should hopefully arrive mid to end March. I'll definately post quite a few images from then on. I live in a place called White River which is situated some 30km from the Kruger National Park and not very far from the escarpment with it's waterfalls, mountains, forests and the Blyde River Canyon. So I've got plenty of places to explore and capture.

 

I'm also lucky in that I'm a Namibian and often travel home to do some work up there. Namibia is just one of those places in the world where it's really difficult to take bad photo's...lol. I'm really looking forward to the M8!

 

Andreas

[nzav]

 

Not enough blue still equals not enough blue, and fiddling with the WB after the fact isn't going to change things :?)

 

 

Andrew,

 

I am not sure what point you are making with that last quote. My reply to the original question was not intended as a seminar on color theory, nor a detailed description of the composition of light sources. I used the most common light source besides daylight as a logical example. There is no room here to cover all possibilities, and incandescent served to make the explanation easy to follow.

 

Of course there are light sources that are missing entire segments of the spectrum, and no amount of filtration can add color; filters do not add color, they only subtract. Common incandescent light sources contain all three primaries; they are just producing less blue than green or red. I did not state by filtering with a blue filter you are adding blue, I stated that you are reducing red and green levels closer to that of the blue component. Another way of looking at it is "Not enough blue" is really too much red and green.

 

The point of my response is by bringing the three primary color levels of your light source as close as possible, you reduce the chances of incurring noise caused by boosting channels in hardware or doing it through software. With R/G/B at reasonably close levels, there will be much less image-destroying amplification of individual color channels.

[woodyspedden]

The one area that I believe still needs traditional filters is where there is the need for grad neutral density for high dynamic range images. I know there are other ways to deal with this e.g. multiple exposures, one for shadows and one for highlights then HDR merge, but I still find the neutral grads to give a more continuous look. It may be me and my lack of experience in this area so I will allow my thoughts to be invalid if that is the case. But for me, using Singh Ray Neutral Grad filters have still provided the most believable images where high dynamic contrast is a critical issue.

Polarization is another area where the processed pictures don't look as natural as ones takes with a real circular polarizer on the end of the shooting hardware.

 

I am probably just being old fashioned here as the techniques I developed for these filters have stood the test of (50 year) time.

 

Best to all in creating the very best images

 

Woody Spedden