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An
example of auto-correction (Auto - Lights) |
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What
is White Balance and Color Cast? |
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Photos
look brownish when taken with a regular daylight film in artificial
light or in candlelight. Often you have mixed daylight and incandescent
light and just want to adjust the tone. Or maybe the outdoors light
is extreme and needs correction - for example you might have a heavy
blue-tone in a scene with a bright blue sky.
The worst scenario is when you have to photograph in a mixture of
fluorescent light and tungsten without any daylight. The example
to the right is one such instance and shows the characteristic strong
green cast. It was filtered with the Auto - Lights method.
Photographers place a blue filter before the lens when taking photos
with a daylight film in artificial light. Typically KB12 (Wratten
80B), but sometimes it needs to be more blue, like if you take pictures
at candlelight, where you will need KB20 (Wratten 78AA). The White-Balance
plugin can correct any discoloration from colored or toned light.
It has presets for standard filters KB20 - KR 20 (Wratten 78AA -
85B+). In addition you can adjust the color of these preset filters
and create even stronger filters if need be.
Auto modes calibrates any filter color for white balance correction.
This is ideal for the notoriously difficult combinations of fluorescent
lights with other light sources. There are three auto modes designed
to handle various colorcast situations. Auto - lights is the most
useful one.
It is also customary to photograph a chart of reference color patches
along with your picture. Power Retouche White Balance Corrector
incorporates the most important such charts (Kodak, Gretag Macbeth,
WhiBal).
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Methods |
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The
White Balance Corrector offers ten methods for white balance correction.
You choose between them from the menu.
Three auto modes designed to suit three typical colorcast problems.
One method for applying digital equivalents of standard Wratten
filters. Also for creating any filter color you may fancy.
One method for picking the color of some brightly lit colored object
in the picture and setting a correction filter from that. Useful
if your brightest objects have a strong color.
Five methods for picking grays from different color rendition charts
that photographers typically photograph into their images.
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Common Controls: Exposure &
Retouch Levels |
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Exposure
Auto Exposure
Offset
Black Point
Alerts
Retouch Levels
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All
methods have these two control groups in common.
Exposure Stops is calibrated from a Fuji chart
of standards and uses the same algorithm as exposure correction
in our BW Studio plugin. Please consult the page about this filter
to see the Fuji chart and comparisons with the filters results.
You will find they are identical.
Auto Exposure will make the plug-in do automatic
exposure correction. You can still use the other sliders to adjust
the image.
Offset and Black Point. Offset
simply makes the entire image brighter or darker. Black Point pulls
the darks towards black. They are a nice couple as you can use offset
to set the images white point and then stretch the darks to set
the black point. Alternatively you can use offset to reach black
and then use the exposure control to reach near white.
Use the Alerts as an aid to set exposure/offset
and black point, or as a help to avoid overexposing the image. Areas
in the image that reach or clip pure white will be colored in the
preview. Likewise, areas that reach or clip pure black will be colored.
You can change the colors of the masks by clicking in the colored
rectangles.
Lights, mid tones, darks. This determines the
strength of the filter in the three different brightness levels.
This means you can apply a filter, for example, full strength to
the mid tones, less strength to the lights and still less in the
darks.
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Adjust Filtercolor |
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Orange - Cyan
Yellow - Violet
Green - Magenta
Filter color
Color picker |
All
methods, except the ones for picking grays on color rendition charts,
allow you to adjust or change the filter color. Instead of the common
RGB controls (red, green, blue) we decided to implement three more
useful sliders: Orange - Cyan, Yellow - Violet and Green - Magenta.
In addition there is a slider to control the intensity of the auto
filter, calculated by the plug-in.
The Orange - Cyan slider is calibrated to match
standard filters for correction of incandescent light or daylight.
The Yellow - Violet slider is calibrated so that
the violet range matches filters for common mixtures of halogen
or tungsten and fluorescent light.
The Green - Magenta slider is calibrated so that
the magenta range matches filters for common fluorescent lights
(this is actually very difficult, because fluorescent light comes
in numerous varieties).
The long colored rectangle shows the current filter color.
Click the long colored rectangle to get a standard color picker
you can select a filter color from or to get more options to adjust
the filter color. Not all colors that can be picked will fall within
the range of possible filters, so the plugin may in some cases change
the picked color to the closest possible filter color.
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Adjust Filtercolor - Correction
Filters (Wratten) |
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If
you select the method Correction Filters - Wratten,
then you will be presented with an extra slider to pick digital
equivalents of common Wratten correction filters for daylight and
incandescent light.
The slider uses the European B&W nomenclature so that -3 is
equal to filter KB3, +12 equal to KR12, etc. Below the slider is
stated the equivalent Wratten filters. The displayed filter color
(in the rectangle) may appear paler than the physical glass or gelatin
filter does to the eye.
The equivalent Wratten range
is as follows...
Remember you can use the Orange - Cyan, Yellow-Violet and
Green-Magenta sliders to create any filter color. If you use
these sliders, the mentioned Wratten filter will still be
the same and will be added to the adjustments. The Orange
- Cyan slider is calibrated to match correction filters
for incandescent light and daylight correction. This means
you can substitute the Wratten filters with it, or make your
wratten filters much stronger than the presets. |
KB |
KB
1.5 = 82A
3 = 82C
6 = 80D
9 = 80C
12 = 80B
15=80A
20 = 78AA
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KR
1.5 = 81A
3 = 81C
6 = 81EF
9 = 85C
12 = 85B
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The following list will give you a hint about what filters to use:
Clear blue sky = 11000K. KR9.
Average Summer Shade = 8000K. KR6.
Clouded sky = 7000. KR3.
Sun 50 dgrs. = 6000K. KR 1.5.
Sun 30 dgrs. (daylight film) = 5500K. No filter required.
Hazy = 4700K. KB3.
Moon light = 4250K. KB6.
200 watt incadescent = 2980K. KB15.
100 watt incadescent = 2900K. KB18.
75 watt incadescent = 2820K. KB20. |
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Brightness range in Correction
Filters Method |
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With
the Correction Filters - Wratten method you get
the option to target the filtering to a specific brightness range.
You can already do this somewhat with theRetouch Levels, but now
you get added control.
Anything darker than the From slider, will not
be changed. Anything brighter than the Up To slider
will likewise remain unchanged. As an aid to setting the sliders,
you can activate the Mask Unchanged mask; this
will apply a color to the unchanged areas (in the preview only).
If the slider Softness is set to 0, then hues within
the chosen range will be changed equally, and as the Softness slider
rises, the effect will fade out from the target value towards the
extremes, thus softly integrating the effect in the whole.
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Color Picker Method |
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Strong colors in the lights
The picked color
Change to color
Workflow
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With
this method the slider Auto-filter % is disabled. The long rectangle
at the top still displays the filter color.
If the brightest lit object in your photo is not white, but, say,
a vivid yellow, then you will want to be able to pick that vivid
yellow and tell the plugin what color it ought to be. The long Change
to rectangle at the bottom displays the color, you want
the pick to be.
When you pick a color, the pick will be displayed in the small rectangle
to the right. Click the button Copy to set the
long rectangle to the same color. When you do this, and if you have
the "Adjust filter color" sliders to 0, then you will
notice the displayed filter color will be white. The plugin automatically
calculates the exact filter that will change the pick to the desired
color and displays the filter color in the top long rectangle.
To set the color of either of the long rectangles, click in it and
you will be presented with a standard color picker where you have
numerous options for adjusting the color.
Bear in mind that what the plugin does is calculate a correction-filter
color, not an exposure correction, so you can't change the filtering
by changing a darker hue of the same color. But selecting a stronger
(more saturated) "Change to" color will have a stronger
effect. A color is usually less saturated if you make it darker,
so the plugin will typically understand a darker selection as a
less strong filter.
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Original photo with strong green
cast. |
Color picker method
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1. Pick a color, The plugin will first automatically try to correct
it to a neutral color.
2. If you are not satisfied with this, click the long rectangle
to open the color picker. Then select what the color should be.
The filter then calculates the difference and sets this as the correction
filter.
3. If you are not happy with this, either use the above three adjust
filtercolor sliders, or click in the long rectangle to get a colorpicker.
Either click in the upper or lower long rectangle.
4. If you want to copy the picked color to the long "change
to" rectangle, then click the copy button. After this click
the "change to" rectangle and it will have the picked
color as default. This can be an aid in choosing the "change
to" color. |
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Gray chart Methods |
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Large Picks
Exposure
Reset
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All
the gray-chart methods have the options for Large Picks
and for adjusting Exposure of the specific
brightness range represented by the gray patch picked.
Large Picks changes the picker from picking the
value of a single pixel to a large group of pixels. Using large
picks helps picking the hue of the object, rather than some random
noise or a film grain.
Exposure will change the exposure of areas in the
photo that have the specific brightness range of the relevant patch.
For example you can change the exposure of the middle gray areas
from 50% to anywhere within 30 to 70%.
Reset will reset all exposure sliders to 0.
You do not have to pick all for the plugin to work. It calibrates
the correction on the basis of your selections.
In order to find out if you need a pick or not, and select the best
picks, you can turn the used picks on and off by removing the tick.
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What are the correct values of
the graychart patches? |
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Photographed patches are usually
brighter |
Manufacturers of color rendition
charts often state the L-value (brightness) of their patches, but
such measurements are made under ideal situations with no scattered
light interfering. In any real photo-situation, the scattered light
in the studio, or out-doors, will cause the patches, especially
the black, to appear brighter than it's formal L-value. The deviation
between the L-value and the actual observed value does not vary
much with various lighting conditions suitable for photographing.
Therefore we could make the plugin take the deviation into account
and calibrate the filter to the photographed patch, rather than
the technically measured L-value of the patch. For example Gretag
Macbeth insist their black patch is true black and should be set
to RGB = (0,0,0) in your photos, but you will find that this is
never true - in fact only true if you place the patch a shadow part
of the picture, which would be quite useless. If you find the filter
does not set the brightness of the patch correctly, you can change
it with the Exposure sliders.
The various brands vary in the kind of black their black-patch has,
and they have adopted various strategies for various reasons. Of
the patches we have implemented, WhiBal offers the darkest black
patch and it is almost a true black when photographed; this is because
it has a silky semi gloss surface which absorbs much light. Gretag
Macbeth offers a mat black, but the very matness causes it to reflect
scattered light off its surface, making it appear off-black when
photographed. Our plugin takes the factors of the various black
patches into account.
If you need a true black patch (rarely, but it can be useful when
photographing paintings of off-black material), then it must be
inside a black box or tube to remove light and reflections (the
opening of which of course points towards the camera) and also semi-glossy
and made of a transparent material because the higher refractive
index will make the patch absorb light, that would otherwise be
reflected off the surface. Glass painted with lamp black oil paint
on the rear side placed at the bottom of a black tube will do well.
The tube should be twice as long as it is wide and about 5 cm wide.
Point it towards the camera and you'll have a true black reference
point. |
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Using Graycards or Whitecards |
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Gray cards
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The Gray Pick methods are made so
that you do not have to pick all available patches. You can pick
just a gray or a white patch. You could also just pick a black,
but that will not produce a good filtering of the light.
We offer two graychart settings. 50% white and 60% white. The standard
Kodak graychart is 50%. Strong light and surface
reflection may cause it to appear brighter when photographed, in
which case 60% may be more appropriate. Also you might often want
a slight brightening of mid tones in which case you can use a 50%
graychart but select the 60% option.
The Gretag Macbeth graychart has it's middle gray
set to 60%.
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WhiBal: 3 or 4 Greys |
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WhiBal
correction cards |
WhiBal
G6 card. This is a single sturdy card with a label
attached. The label is a white and a black patch. If you use
the WhiBal G6 card use the regular white and black pickers
in the plug-in, but of the two grays, use the light grey.
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WhiBal
originally was a set of four thick plastic cards for white
balance correction. It came with a white, a black and two
grays. If you use this set of cards, use all four pickers
in the plug-in.
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Visit the WhiBal homepage here.
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Gretag Macbeth Color Rendition
Chart (24 patch): 6 Grays |
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Gretag Macbeth correction
chart |
Gretag
Macbeth Color Rendition Chart is a standard color reference chart
used by photographers. PowerRetouche has expanded the charts use
for digital photography by implementing white balance correction
from the six gray patches. You do not have to pick all six.
Visit the Gretag Macbeth homepage here.
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Auto - lights |
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Auto
- Lights |
In Auto Lights the plugin
scans the photo to determine the color of the light in the photo.
It then calibrates a filter color to correct white balance and remove
color cast.
Here's an example of pure Auto Lights filtering. The left photo
is the original:
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Auto - midtones |
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If your picture is mainly
in the midtone range, or the colorcast is most pronounced in the
midtones -- like in the example just below -- the Auto - Midtones
method will suit you.

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The above photo will not be suited
for the auto-lights method for another reason, which is important
to note: The brightest areas of the photo (the green grass
to the right) does not show any color cast so it will trick
the plug-in to adopt a wrong filter. In this photo the face
has the color cast we want to remove in the midtones.
We would probably want to correct the exposure also, so this
we did in the example to the right (We raised exposure and
offset, then deepened the blacks. All within the White Balance
plug-in in one go): |

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Auto - mid tones is particularly suited for correcting portraits
where you want some of the color of the light preserved or especially
want to preserve the cool reflected lights so typical for skin photographed
out-doors. The face being of course in the mid tone range and the
filter thus correcting mainly the face more than the reflected lights
and strong shadows.
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Original - With a heavy blue
cast from a clear blue sky.
You can see this because mainly the lights are blue, but we
want to preserve the cold/warm contrast of the light/shade,
so we won't use auto - light correction. |
Auto - mid tones
Filter adjusted slightly red:
Yellow 10
Magenta 10
The remaining blue in the lights accentuates that this is
an out-doors photo. |
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Auto - Colorcast |
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Original - This could have
been a nice warm picture, but a blue colorcast ruins it. |
Auto - Colorcast
Exposure + 0.99
Black Point 30 |
Filter color adjusted
Yellow 10
Magenta 10 |
As you can see from the middle image, Auto - Colorcast
correctly removes the colorcast from both the light, mid tones and
darks. But the picture still does not have the warm tone appropriate
for the occasion, so in the last example we adjusted the filter
color. |
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Brightness range Example |
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Target
color cast removal |

Original with a heavy blue color cast
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Target the filter progressively
to lights and mid tones

Note the reflections in the lake are toned perfectly |
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