Warm up filters and digital photography

For digital cameras, is warm up filters necessary considering the

fact the the software will have this function?

 

Can some experts provide some places where a warm up filters can be

used for optimum effect? Like potraits?

 

Thanks.

Hi Andy, There are two schools of thought: Some say get everything "right" (whatever that might entail) in the shot so there's less fuss later in Photoshop. Some might ask why shell out for a decent filter if I can get the same effect in PS? So I think you may find reasonable people disagree on which is better. Warming filters can help when shooting where the light is "cool" - for example, in shady woods. Some polarizing filters come in "warm" versions (Moose Peterson has one) because polarizers can "cool down" a scene.

A WARMING filter achieves this by raising (or lowering, depending how you look at it) the temperature. For example: if you are using a daylight film rated at 5200K you could use a filter that brings the temperature up to 6000K (or whatever value you want) and get a "warmer" image.

 

Since such temperature control is now available on most DSRL (by manually setting a K value to your liking) filters are no longer needed...thankfully!

An alternative to using warming filters is to use a warm corrected white balance. Probably the easiest way of doing this is using custom white balance and something like Warm cards (which are actually offwhite in a slightly cooler complementary shade, so the custom white balance corrects for the apparently cooler white). An advantage with that route is that is should give a predictable degree of warmness to the image regardless of the actual lighting.

 

http://www.warmcards.com/

 

or

 

http://www.expodisc.com/products/product_detail.aspx?id=MTAwMA==

 

The advantage is that you don't have to worry about potential flare or vignetting from an additional filter. Tweaking white balance in this way applies to the whole image, so it doesn't replace the effect of something like a tobacco grad filter that you might use to liven up a landscape shot on a dull day. This unofficial guide to the Cokin filter system has some very useful examples and information about the use of coloured filters and other effects:

 

http://www.geocities.com/cokinfiltersystem/

 

Optical filters are quicker to use, although where they filter out a lot of the light in one particular RGB channel, the lack of detail recorded in that channel by the sensor will tend to reduce the sharpness of the image - the demosaicing software has less information to reconstruct image detail from. Many filter effects can be produced by skilled image editing, in some cases achieving things that would be difficult with an optical filter. The big exceptions to this involve the use of polarizers (since your image won't have information if it is obliterated by a specular reflection), and higher factor neutral density filters (an extreme example is a solar filter that will allow you to photograph eclipses and sunspots) that allow you to use very slow shutter speeds in daylight conditions.

 

In environments with e.g. windblown sand or spray or where fingers may poke at the front of a lens a UV filter does offer protection for your lens that a hood can't quite manage.

If you are shooting JPEG then the closer you can get the exposure the better since you don't have that much room to edit. Small adjustments such as those provided by the Skylight filters are easily accomplished and I would expect that you can get the effect of an 81A without problem.

 

I have little to add to Mark U's excellent response except to add that you should not use warming filters and leave the camera on AWB. The camera will work hard to remove the effect of the filter. I no longer use any colour correction or warming and cooling filters on my 20D.

 

I don't use grad coloured filters but very occasionally I still use graduated neutral density filters (when not using a tripod or movement is a problem) and I regularly use a polarizer.

<i>"where they (optical filters) filter out a lot of the light in one particular RGB channel, the lack of detail recorded in that channel by the sensor will tend to reduce the sharpness of the image - the demosaicing software has less information to reconstruct image detail from."</i>

<p>

If you're using the filter to restore white balance to daylight, exactly the OPPOSITE is true. The filter brought the R,G and B channels back into proper proportion, and exposure is typically increased to compensate for the filter's light loss, giving the demosaicing software MORE information to reconstruct image detail.

<p>Or are you suggesting that dimmer daylight, compensated for by increased exposure, will result in less sharpness than an out of balance white balance?

<p>

Having said that, I still do not use color balancing filters for 2 main reasons:

<p>

1) Convenience.

<p>2) Accuracy. Does an 81B (or whatever) correct as accurately as my RAW converter? Probably not. Does this overcast sky need 81B or 81C? Does this amount of shade, with the surrounding reflected sunlight, require an 81EF? Are those 60 watt or 100 watt incandescent bulbs that I'm trying to balance? How much warmth do I want to leave in the incandescent scene? I find it much easier to get exactly what I want in the RAW conversion than in selecting filters.

Warm filter is useless with digital photography.

 

First if you shoot under auto white balance, it;s like the fliter is not there anyway..

 

If you shoot in any setting, you can set the color balance so why use a filter at all ?

I think Leonard is thinking of using filters for colour correction to match the response of a film emulsion. The whole point of using a filter (or equivalent white balance tweak) with a digital camera is to change the colour balance in a predictable way from a true white balance setting (I think Danny missed this point too). Perhaps he didn't read what I wrote sufficiently closely, but for example if you were to use a red filter to create an artificial sunset scene (maybe a slightly extreme example of a warm-up filter), then you would have almost no information in the blue and green channels, so the demosaicing software would be left to rely on the red channel with just 1/4 of the pixels to generate luminance information and image detail. The same considerations apply to the use of filters for images that are intended to be printed as B&W - do it in software, not as you would with a film camera.