Multi Color Balance

This transformation lets you add or remove color casts from an image. Different color casts may be removed from different parts of the tonal range. Initially, color balance starts out with just shadow and highlight cast removal, but you can create up to nine casts to remove based on different tonal values.

This transformation is a more powerful version of the much simpler Color Balance transformation which is limited to removing the same color cast from the entire tonal range. For basic color balancing, you will probably find the basic transformation easier to use and adequate for many images.

Removing a color cast means making colors that match that color become neutral; adding a color cast is the reverse; it makes neutrals take on that color. Removing a color cast is like passing an image through a filter whose color is the complement of the color cast; adding a color cast is like passing an image through a filter whose color is the same color as the cast. Removing and adding a color cast at the same time makes colors which match the remove cast become the color of the add cast.

For example, to remove a greenish cast from an image, select a greenish color to remove. The more saturated you make the cast to remove, the more green you take out of the image. To add a warming cast to an image to simulate early morning or late afternoon light, add an orange cast. Again, the more saturated the color, the stronger the effect.

The color balance transformation works by creating and applying three curves to the input image -- one for the red channel, one for green channel, and one for the blue channel. These curves are displayed on the right side of the dialog box. You can save these color curves for later use with the Color Curves transformation via the Settings menu.

Each curve is defined by up to nine points corresponding to the current color selections. You can either set the curves by choosing color casts to add and remove, or when individual channel curves are displayed you can drag points on the curve to select the colors.

Rows of color patches are displayed down the left side of the dialog box -- these are the colors to remove and add for various brightness levels.

Initially there are only two rows (one for shadows and one for highlights) but you can add more rows to alter the color balance for up to nine total mid-tone brightness levels. To create a new row, shift-click on the input image at a location of intermediate brightness and that you would like to make neutral in the output image. This will add a new row for that brightness level and automatically remove the color in the image and add a neutral gray of the same luminance. Rows are always sorted in ascending brightness order.

In some extreme cases or when adjacent brightness levels are close, the remove and add colors may be inconsistent and curves cannot be generated from them that do not create solarization. When this happens the Status for the inconsistent colors is set to err. In addition, you can temporarily disable or enable rows by clicking their Use checkbox. Clicking on any of these patches pops up a color picker you can use to set its color manually. The status for auto black and auto white colors is set to auto -- note that editing these colors manually will turn off the auto setting and disable auto black or white.

The color curves that correspond to the current multi color balance settings are displayed on the right side of the dialog box. The tabs at the bottom let you select which channel to display (Red, Green or Blue). If you select RGB, all three channels are superimposed. You can drag the control points on the curves which adjusts the corresponding colors accordingly.

Tool Bars

Delete Tool Bar

This one-button tool bar lets you delete the currently selected row. Rows are selected by clicking the corresponding radio button in the Sel column (see above).

Auto White Balance Tool Bar

This tool bar lets you control auto white balancing. Auto white balancing can be turned off, turned on, or turned on with auto expansion to full white. When auto white balancing is selected, Picture Window scans the input image to identify the brightest colors and averages them to generate the remove color.

The add color is set to a neutral gray of the same luminance as the remove color unless auto expansion is selected in which case the add color is set to pure white. This causes the lightest colors in the input image to become pure white in the output image.

Auto Black Balance Tool Bar

This tool bar lets you control auto black balancing. Auto black balancing can the turned off, turned on, or turned on with auto expansion to full black. When auto black balancing is selected, Picture Window scans the input image to identify the darkest colors and averages them to generate the remove color.

The add color is set to a neutral gray of the same luminance as the remove color unless auto expansion is selected in which case the add color is set to pure black. This causes the darkest colors in the input image to become pure black in the output image.

Settings Menu

Save Color Curves...

This option lets you save the current set of curves as a color curves file for later use with the Color Curves transformation. For example, if you have a copy stand with its own lighting, you can create a set of color curves by photographing a step wedge. The resulting curves can then be used to color correct any other photo you take with the same setup by loading them into the Color Curves transformation.

If you have a Macbeth ColorChecker (see below), you achieve a similar result using the Match Reference transformation.

White Threshold -- The White Threshold options (Low/Medium/High) apply only when Auto White Balance is in effect. They adjust the internal threshold used when computing the input image white point. Normally a low threshold works best, but it the input image is overexposed or some of the highlights are clipped, a larger threshold may work better, although it can result in the clipped highlights being tinted.

Black Threshold -- The Black Threshold options (Low/Medium/High) apply only when Auto Black Balance is in effect. They adjust the internal threshold used when computing the input image black point. Normally a low threshold works best, but it the input image is underexposed or some of the shadows are clipped, a larger threshold may work better, although it can result in the clipped shadows being tinted.

Probe Size (1x1/3x3/5x5/7x7/9x9)

These options let you control the sample size used by the probe, should you choose to use it to select colors from the input image. Larger probe sizes are useful for obtaining an average reading of any area of the image that does not have a smooth texture; smaller probe sizes let you get precise readings of very small areas. The currently selected probe size is shown with a check mark.

Amount

The amount control lets you control how much of the color balance transformation is applied to the input image. You can apply a percentage of the transformation to the entire image, or you can specify an amount mask to restrict the effects of the transformation to only part of the input image.

Tips

Highlight casts are the most important

The human eye is more sensitive to bright colors than to dark colors. For this reason, highlight color casts are the most important setting. In most cases, you can use a highlight cast alone to do all of your color balancing.

Using a white balance card

Try photographing a step wedge -- a card with a graduated set of gray patches. This is particularly useful for work on a copy stand with tungsten lighting or other studio work. By creating a color to remove for each gray level, you can generate a set of color curves you can use to correct subsequent images taken under the same lighting conditions.

Using midtone probes

Some images, especially those scanned from color negatives or from faded film or prints have different color casts in different parts of their tonal range. To remove this type of cast, create multiple colors to remove taken from lighter and darker parts of the image. Correction curves are then generated automatically.

Correcting for fluorescent lighting

Fluorescent lights often introduce a greenish cast to photographs. Removing this cast, especially from scans of color negatives, often requires use of midtone casts as well as a highlight cast. Set your highlight cast first to get the image highlights the right color and then work on the midtones. In an image with mixed fluorescent and other lighting, you may have to create masks to isolate the areas illuminated by different light sources and balance them separately.

Adjusting dynamic range

To adjust the dynamic range of an image, first set highlight and shadow to auto and bring up color pickers for the highlight and shadow casts to add by clicking on their respective color patches. To increase the dynamic range, move the value slider of the highlight color picker up and the slider of the shadow color picker down. This makes the highlights brighter and the shadows darker. Moving the sliders in the opposite directions reduces the dynamic range of the image.