EXCERPT: Professional Filter Techniques for Digital Photographers

200703we_filtertech_ In his newest book, "Professional Filter Techniques for Digital Photographers" (Amherst Media; $34.95) pro photographer Stan Sholik covers the gamut of possibilities and applications now available to the digital photographer through traditional (hardware) filters and filter software.

He advises on how to select your best filter options for your photographic style and how implementing the device will impact your photos. Covering filters used for color correction, contrast enhancement, soft focus, and a full spectrum of interesting, artistic effects, this book will satisfy your quest for technical precision and your yearning for greater creative expression.

Features:

  • Comparisons of effects achieved using traditional vs. digital filters
  • Charts that allow readers to predict effects of a variety of filter types
  • Page after page of analyses of top filters

In this excerpt, Sholik examines color converting, light balancing and compensation filters.

EXCERPT: "Professional Filter Techniques for Digital Photographers" by Stan Sholik

Images ©Stan Sholik

Chapter 2
Color Converting, Light Balancing and Compensating Filters

One of the tremendous benefits that digital cameras has brought to photographers is the ability to achieve pleasing color under a wide range of lighting conditions, from daylight to incandescent to fluorescent. But does this mean that you no longer need to use color converting filters (80- and 85-series), light balancing (81- and 82-series) or color correcting filters (such as CC30 Magenta for cool-white fluorescents) over the lens while shooting? The answer is a qualified “Yes”: you don’t really need these filters, as long as you are shooting in RAW mode and don’t need absolutely accurate color right out of the camera. However, if you are saving images as JPEGs, using color converting or light balancing filters on the lens and setting the camera white balance to “Daylight” will give the most accurate color.

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Not every scene needs a neutral color balance. This image contains daylight, fluorescent and incandescent sources, so I just set the camera on Daylight and shot to see what it would look like, and I liked the result.

The reason is simple enough. The red, green and blue micro-filters used on digital sensors (see Appendix) only correct for a very narrow range of red, green and blue. Think of all the colors that you call “red” and you’ll see the problem. So engineers select filters for each of the three colors that work well with daylight and electronic flash since the majority of photos are taken with those light sources.

Correcting for cloudy and shade conditions isn’t too tricky and works well since the correction is fairly minor and involves using less of the blue channel, which always needs the most amplification. Correcting for incandescent and fluorescent lighting however involves large changes. Incandescent lighting in particular is tricky as it requires a major increase in the blue channel (think of an 80A filter that corrects 3200 degree Kelvin light to daylight balance). Correcting fluorescent light is also tricky for the engineers since there are a number of different types of tubes and they all change color at different rates as they age.

Digital cameras allow photographers to color balance for different types of light sources while you shoot. In most cases this works well. These color charts were all shot under controlled conditions in my studio and saved as JPEGs in my Nikon D1X. I then moved them into my computer and, using Photoshop Curves eyedroppers, set the white, black and gray balance of the white black and mid-tone gray to the same values, letting the colors fall as they would. With luck the differences in color will hold up in printing.

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The chart labeled Daylight/Flash (above) was taken with the camera set on Daylight balance with studio flash equipment that very closely matches the color temperature (5200 degrees Kelvin) of the D1X Daylight setting. This is the most accurate color rendition of the color chart.

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The Flash/Flash chart (above) is slightly warmer because of the difference in color temperature of the Flash setting in the D1X. This was taken with the same studio flash unit at the D1X Flash setting.

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The D1X does a good job with the cool white fluorescent lights in my studio on the Fluorescent setting as you can see in the chart labeled Fluorescent/Fluorescent (above).

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Colors suffer in the Incandescent/3200 chart (above) because the D1X uses 3000 Kelvin for this setting rather than the 3200 Kelvin of my studio lights.

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The colors are much closer to the Daylight/Flash reference chart in the chart labeled Daylight/3200/80A (above) where I used the D1X Daylight setting and an 80A color converting gelatin filter with the 3200 Kelvin lights.

 

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When I didn’t use an 80A filter with the D1X set to Daylight and 3200 Kelvin lights, then tried to correct the JPEG, the results are shown in the color chart labeled Daylight/3200/No Filter (above). Only the white, black and mid-tone gray patches are the same as those on the other charts and this is thanks to Photoshop.

Fortunately, with a combination of camera and software filters, you can correct images made with nearly any light source to a neutral color balance. And if neutral isn’t what you’re looking for, you can use hardware and software filters to achieve that look also.

Color Converting Filters

Whenever you shoot with a digital camera, I recommend not using the “Auto” color balance setting, particularly if the lighting conditions are tricky. I also recommend using the “RAW” capture mode, even though this means less captures on the camera’s media card and additional time later on the computer to process the images.

Shooting in “Auto” color mode can give a slightly different color balance with each capture, even when the lighting conditions don’t change. Digital sensors are much more sensitive to color balance changes than we are. Shooting in one of the preset modes (Sunlight, Shade, Cloudy, etc.) locks in a color balance. If you need to covert or correct the images later, you can do it in a batch once you determine the correction needed.

Shooting in “RAW” has a similar advantage. You can use the manufacturer’s RAW conversion software to change from one preset to another with the same result that you would have obtained if you had set the camera to that preset.

For example, if you are making RAW captures with the Sunlight preset in the sun, then move indoors without changing the preset, the photos will have a yellow cast from the incandescent light indoors when you view the RAW image on the computer screen. By selecting “Incandescent” as a color balance in the RAW conversion software for these images, the yellow cast will be minimized, exactly as it would have been if you had reset your camera to Incandescent before you took the pictures.

But what if you are shooting JPEGs and do this? Now you have a problem, since the manufacturer’s software will likely be of little help. Making the conversion in an image processing program like Photoshop is tricky, time-consuming and will often leave big gaps in the histogram.

Fortunately, there are two solutions for JPEG shooters. One is to use a conversion filter over the lens. But if you could remember to do this, you could remember to change the preset on the camera. The other solution is to use a software filter. An advantage of the software filter, besides not having to purchase and carry a hardware filter, is that it requires no increase in exposure when shooting. In either case, to use them correctly, you will need to know a little about the way these color conversion filters are numbered.

Filter designations

If you capture JPEG images in daylight with the Incandescent setting, they will look blue, and one of the 85 series of amber conversion software filters is needed. If they were taken with incandescent lights with one of the outdoor settings, they will look yellow, and you will need one of the 80 series of blue filters to correct the photo. Later in the chapter we will address fluorescent light filters and correcting for shade and overcast on a Sunlight setting.

The three filters of the amber 85 series (85, 85B, 85C) only need to remove some of the blue present to convert daylight to the proper balance to correct for the Incandescent setting. The 85C filter gives the least warming followed by the 85, then the 85B that gives the most. The 85B is the one to choose most often, though more correction may be needed.

The four filters of the 80 series (80A, 80B, 80C, 80D) balance the color temperature of incandescent light sources if one of the daylight settings was used by mistake. The 80A, which converts incandescent theatrical stage lights to daylight balance, is a good place to start, as it is the strongest of the four. But even it may not be enough if the light sources are household bulbs. The 80B gives less correction than the 80A, the 80C less than the 80B and the 80D the least of all.

Both the 80- and 85-series filters can be used in combination, on the lens or in software.

If you are using Photoshop CS or CS2 or Photoshop Elements 3.0, Adobe has built in an 80 filter and an 85 filter. They are found in the Filter/New Adjustment Layer/Photo Filter flyout. However, my favorite software plug-in program for color conversion filters is the Color Conversion tool in the 55mm collection from Digital Film Tools.

To convert the image using the Color Conversion tool you must have it open in your favorite image-editing program. When you select the 55mm collection from your Filters or Effects menu, the full list of 55mm filters is displayed. When you choose Color Conversion, a preview image opens in the 55mm window, with a drop-down menu of pre-built filters with a row of sliders beneath. The sliders allow you to adjust the opacity of the filter, the overall exposure and the amount of color in the highlights. You simply choose the filter, adjust the sliders until it looks good in the preview and apply the filter with the “OK” button. There is even a drop-down menu that allows you to toggle between the original image and the filtered version.

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The 55mm collection from Digital Film Tools includes many filters in its drop-down menu. Choose Color Conversion to make the large change in color temperature that is needed for this wedding photo taken in mixed lighting with a Daylight setting on the digital camera.

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I didn’t want to correct this image to neutral. I like the warmth, but there is too much red in the groom’s face. The 55mm filter interface has a drop-down listing of the color conversion filters. The 80D works well with this image, leaving some of the warmth while reducing the excessive red in the groom’s face. Later, a Curves correction could improve contrast and make any other slight correction in color.

The Photo Filters in Photoshop create an adjustment layer automatically, but many plug-ins, including the 55mm filters do not. When using these strong software filters, or any software filters for that matter, be sure to first duplicate the image you are working on to a new layer, then apply the filter. That way you will always have the unfiltered image to return to if you don’t like what you have done at some point in the future.

While color-conversion filters were created for specific technical purposes, their use as creative tools is what draws many photographers to them. The strong effect that color-conversion filters have on light makes them appropriate as mood enhancers in photography.

Heavily overcast and foggy days keep most photographers at home. But these types of days are perfect for shooting with a blue 80A filter over the lens or later on the computer to create a moody, monochromatic otherworldly effect.

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02_04b

The D1X delivered the rendition (top) of heavily overcast early morning on a lake in Canada. To me it felt colder than this so I added an 80A filter, above. The canoeist was a bonus.

Indoor scenes with incandescent light don't need to be corrected back to neutral. In many cases, the warmth of the scene can be an important element of the photo. Using an 85 series filter in software will enhance that warm mood that an Incandescent preset will minimize.

Warming filters are also useful for enhancing sunset photos. While other filters specifically designed for this purpose will be discussed in Chapter 4, any of the 85 series of color conversion filters will add significant warmth to the sky as well as the foreground. This effect is strongest in the midtones and shadows and the overall, nearly monochromatic effect serves to tie the sky and foreground together in a feeling of "sunset" rather than simply a photo of a sunset.

Light Balancing Filters

Like color conversion filters, light-balancing filters are designed to adjust the color temperature of the light. The adjustment they offer, however, is much smaller. These are the filters to use for moving back and forth between Sunlight, Shade and Overcast presets.

There are two series of light-balancing filters, the bluish 82 series and the straw-colored 81 series. The cooling 82 series has four members, 82, 82A, 82B and 82C. This time the numbering is logical, with the 82 giving the least correction and the 82C the most.

There are six members of the 81 series of warming filters: 81, 81A, 81B, 81C, 81D and 81EF. These too progress logically in correction from the 81 with the least to the 81EF with the most correction.

Additional shifts in color temperature can be accomplished by combining filters within each light-balancing series or in combination with color conversion filters. The most common use of light-balancing filters in many applications is for noticeable "warming" and "cooling." Since their effect on color temperature is so much less than color correction filters, the warming and cooling is far subtler.

Filters in the bluish 82 series are effective in reducing some of the excess red in late afternoon sunlight, minimizing the ruddy red "sunburned" look from front-lit portraits taken during this time of day.

Some digital portrait and fashion photographers find the warming effect of the straw-colored 81 series so appealing that they use one, usually an 81 or 81A, on their lens at all times to warm up flesh tones. Both of these filters add a pleasant warmth to portraits taken indoors or out. The 81B, 81C and 81D filters are also useful for this, but their effect is more visible if there are obvious neutral colors in the photo.

Where the important elements of a composition are entirely in open shade or lit by an overcast sky, the 81EF filter eliminates the cool blue cast and yields a warm, natural-looking skin tone. This is the hardware filter that the camera manufacturer tries to duplicate with the Shade preset.

In software, Photoshop CS, CS2 and Elements 3.0 or greater include an 81 and 82 filter, but for the full set, 55mm from Digital Film Tools is the best choice again. The 81 and 82 series filters are found in the Light Balancing set. Remember to duplicate the original to a new layer before applying the filter.

02_05a 02_05b

The left photo, taken in open shade on the Daylight setting with a Kodak DCS Pro SLR/c, is too blue. Using the 81EF filter setting in the 55mm Light Balancing plug-in set, I quickly enhanced it to the version to the right.

Another plug-in, PowerRetouche, has combined many, but not all, of the color conversion and light balancing filters with other tools in its White Balance set. Choosing the “Wratten Filter” option from the drop-down menu box at the top of the screen activates this option. A slider lets you select the available filters. There are also sliders to allow you to fine tune the color of the filter. With the Wratten filter set to “zero,” these sliders allow you to change the overall color in every imaginable way.

PowerRetouche White Balance even provides a slider that gives you control over the range of gray values that are changed by the color adjustment, effectively creating a luminosity mask. You can correct a range of highlights with one application, a different range of highlights with another application, on down through the full range of gray values. This is a very powerful tool with many possible options and it can be overwhelming until you experiment with it for a time. Fortunately the preview window is very helpful in showing you the results of your experiments.

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The White Balance set in the PowerRetouche plug-in provides a Wratten filter setting with some, but not all of the Wratten light balancing filters. You are also able to target the correction to light, midtone or dark values and even to a limited number of colors of the spectrum. Once you become familiar with the interface, the amount of control you have is tremendous.

Professional photographers not only use filters on their lenses, they also use them over their lights to warm or cool the light. With this method, the light on a model can be warmed and the light on the background can be cooled. No filter is used over the lens, eliminating the chance of flare reducing the image quality. The most popular filters for this purpose are Rosco Color Temperature (CT) gels. Blue (B) is used to cool the light and Orange (O) to warm the light. They come in varying strengths.

PixelGenius, in their PhotoKit Color series includes CT-B and CT-O software filters in strengths of 1/8, 1/4, 1/2, 3/4 and full. The PixelGenius filters are put in the File/Automate menu. When you apply them, they create a new layer for the filter, like a Photoshop adjustment layer, so the original image remains. You can then create a layer mask for the filter and apply it anywhere you choose.

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The PhotoKit Color series of plug-ins from PixelGenius operate from the File/Automate menu in Photoshop. Included are the equivalent of Rosco Color Temperature (CT) filters that studio photographers put over their lights to increase or decrease their color temperature.

All of the filter sets from PixelGenius function from the Automate menu in Photoshop and this is a truly elegant way to allow photographers a high level of control over the application of the filter.

Another trick that professionals use is a reflector board opposite the main light while making portraits. This board could be white for a diffuse fill with the same color temperature as the main light, gold for a warm look on the shadow side of the face, or silver, for a brighter, harder reflection. Software tools with these names are available in the Digital Film Tools 55mm and Nik Software Color Efex Pro Traditional software filter sets.

The Gold Reflector in the 55mm set opens a preview image and sliders to adjust the effect. While it does add warmth to the shadows as a gold reflector board would, the filter adds more warmth to the highlights than I like to see.

I personally prefer the Gold, Soft Gold and Silver Reflectors from Nik, but only when they are applied through the Nik Color Efex 2.0 Pro Selective tools. These tools, like the PixelGenius filters, are found in the Automate menu in Photoshop. If you are using another image-editing program, you will need to apply them globally, like the 55mm filters, from the Filter menu.

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The Nik Color Efex 2.0 Pro Selective tool lets you brush on effects simulating the use of silver, gold or soft gold reflectors in Photoshop. This screen capture shows the image after the Soft Gold Reflector has been applied to the shadow side of the model’s face and to the gold badge.

Using the Selective tools in Photoshop, any Nik filter can be painted into the image. The Nik software automatically creates a new layer with the filter applied and a layer mask filled with black. As you paint in the filter effect, the layer mask is removed. Painting with 100% opacity paints the layer mask with white. Painting with a lower opacity paints the layer mask with a corresponding value of gray. Again, very elegant and with a level of ease and control that is welcome for Photoshop owners.

Used creatively, light-balancing filters, like color correction filters, impart an overall "mood" to a photo, but to a lesser extent. Both types can be used to tie the foreground and background together. In doing so, they tend to reduce overall contrast by giving the photo more of a monochromatic look.

Color Compensating Filters

Both color-correction and light-balancing filters adjust the proportion of yellow/red to blue/cyan in the light, either absorbing blue/cyan or yellow/red. Their effect is fairly broad across the visible spectrum.

Sometimes it is useful target more specific areas of the spectrum, because imbalances can occur in the proportion of all components of incident light. These imbalances are corrected by color-compensating (CC) filters, which can also give a photographer precise control over the creative color rendering of the subject.

Color-compensating filters are available in seven strengths, in both the additive (red, green, blue) and subtractive (yellow, magenta, cyan) primary colors. If you are shooting JPEGs or even RAW images with cool white fluorescent lighting, using a CC30 Magenta filter will give you a more color-balanced original than using the Fluorescent preset in most digital cameras.

Used creatively, the stronger color-compensating filters can be used much like the color-correction or light-balancing filters to create "mood," or an almost monochromatic effect by tying foreground and background together with color. The range of colors is far greater however with color-compensating filters.

The stronger filters are also effectively used to increase the color saturation in a monochromatic photo. Taking a close-up photo of a white rose with a CC50Y filter will add color to the flower and minimize any small color defects it might have.

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You can use strongly colored color compensating filters to change the color of subjects if there are no other subjects in the shot. Here a white rose, above, is changed into a pale yellow rose, below, with the use of a CC50Y filter over the camera lens. This could easily be done in software also.

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Applied in post-production, there are two options. The rose can be selected first and the filter applied to the selection, or the filter can be applied overall and an image mask used to remove the filter from outside the rose.

Similarly, the weaker color-compensating filters can be used to subtly intensify a color by using a filter the same color as the subject, or subdue color by using a complementary filter, while having little effect on highlights and shadows. A color of a pale yellow rose will seem more intense when photographed with a CC20Y filter, or even paler with a CC10B, but the fence will still look white to the eye.

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Less intense color compensating filters are appropriate if you want to subtly increase the saturation of a particular color. This is done by using a CC filter close to the color of the subject. The yellow rose, above, was enhanced with a CC20Y filter to produce the result below.

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Color compensating filters are available as software filters also, and again the 55mm Filters from Digital Film are the best. All of the colors from the weakest density, 05, to the strongest, 50, are included. To my eye, they function just like their hardware equivalents. Just remember to duplicate your image first, because these filters are applied directly to the image, not to an adjustment layer.
In the computer, the filter could be applied to the entire image or just the yellow rose by either of the methods described above.

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Cholla cactus are grayish-green in real life, but a CC30G filter adds some color and life to them.

For use on the camera lens, color-compensating filters are usually purchased as gelatin or polyester because many photographers carry a large number of them. They are also available in resin or glass from some manufacturers.

Color-conversion, light-balancing and color compensating filters are readily available in all forms: gelatin, polyester (mounted and unmounted), resin and glass (uncoated, coated and multi-coated).
For post-production work, I highly recommend the color-conversion, light-balancing and color compensating filters found in the 55mm filter set from Digital Film Tools.


One Other Option: ExpoDisc

There is another device on the market that I have found very useful when I need to create an accurate white (or warm white) balance while shooting. It is the ExpoDisc and is available as a screw-in filter for lenses with standard filter diameters from 49mm to 82mm and a slide-in for the Lee filter holder.

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When you need a neutral color balance, even in mixed lighting, I have found no better tool than the ExpoDisc. By placing it over the camera lens and using the camera’s custom white balance tool, you quickly and easily balance the digital sensor to whatever lighting conditions exist.

With the ExpoDisc, you can leave your meters, gray cards and color charts at home. This patented device allows you to accurately determine exposure and white balance in a few simple steps and, once these settings are stored in your digital camera, to capture images without worrying about these settings until the lighting conditions change.

The simplicity of the ExpoDisc is striking. It consists of a neutral, prism-textured plastic disc on one side and a neutral plastic diffusion disc on the other. Sandwiched between the two are color correction filters. There are two versions of the ExpoDisc: the Digital White Balance Filter that gives a neutral color balance and the Digital Warm Balance Filter that gives the warmth of an 81EF filter.

For neutral white balancing, each unit is individually calibrated to ensure that incident white light (light whose red, green and blue components are present in equal amounts) is transmitted through the filter with equal red, green and blue (RGB) values emerging on the other side. With the ExpoDisc mounted over the lens under shooting conditions, the white balance software in the camera reads the RGB values of the light transmitted by the ExpoDisc and, if they are not equal, makes a corresponding adjustment to equalize them.

The Warm Balancing Filter works the same way, but its slightly blue bias fools the camera’s white balance so that it warms the images captured.

The exact procedure for this white balance process varies from camera to camera. The instruction sheet packaged with the product gives general procedures and the ExpoDisc web site, www.expodisc.com, gives specific steps for different camera bodies. All that needs to be done is to perform a custom white balance with the ExpoDisc over the lens, save the result as a preset and capture images.

If you’re shooting JPEGs, the ExpoDisc will give you extremely accurate color correction, either neutral or warm balance. And for those photographers shooting RAW files, the ExpoDiscs are equally valuable. Simply make a capture or exposure through the ExpoDisc and use this frame to white balance in postproduction or for the photo lab to use to gray balance the proofs. ExpoDiscs are truly useful, versatile and highly recommended.

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This page contains a single entry from the blog posted on March 1, 2007 12:29 PM.

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