Colors Tools ¶

Encoding Depth ¶

Here you can change the encoding depth per color channel of the edited image. 8 bit encoding is the common JPEG format, 16 bit encoding is better suited for high quality images, but this format needs more storage space, calculation time and is currently available with PNG, PGF, TIFF, and JPEG-2000 formats only.

备注

When you re-encoding an image from 8-bit to 16-bit, uniformly distributed noise is introduced to prevent histogram holes due to colors range expansion.

重要

HEIF, AVIF, JPX formats can encode as 8 bits or 12 bit. WEBP is limited to 8 bits. These limitations can change in the future.

Color Management ¶

This tool allows to convert image from one color space to another one. Its use is the change and assignment of color profiles to an image. For detailed instructions on the use of color profiles, please refer to Color Management Rules and Color Management Settings sections.

The Image Editor to Change Image Color Space¶

Auto-Correction ¶

This tool set provides five automatic correction levels that will improve an image in most cases. Use this tool before going into the more involved manual adjustments.

The Auto Levels, Normalize, Equalize, Stretch Contrast, and Auto Exposure available from Color ‣ Auto-Correction… menu entry menu will attempt to work out the best color levels automatically. You will need to experiment with the effects of these functions to see what works best with your photograph.

Auto Levels: This option maximizes the tonal range in the Red, Green, and Blue channels. It searches the image shadow and highlight limit values and adjusts the Red, Green, and Blue channels to a full histogram range.

Normalize: this method scales brightness values across the selected image so that the darkest point becomes black, and the brightest point becomes as bright as possible without altering its hue. This is often a “magic fix” for images that are dim or washed out.

Equalize: this method adjusts the brightness of colors across the selected image so that the histogram for the Value channel is as flat as possible, that is, so that each possible brightness value appears at about the same number of pixels as each other value. Sometimes Equalize works wonderfully at enhancing the contrasts of an image. Other times it gives garbage. It is a very powerful operation, which can either work miracles on an image or destroy it.

Stretch Contrast: this method enhances the contrast and brightness of the RGB values of an image by stretching the lowest and highest values to their fullest range, adjusting everything in between. This is noticeable only with washed-out images and can be a good fix-it tool for bad photographs.

Auto Exposure: This option enhances the contrast and brightness of the RGB values of an image to calculate optimal exposition and black level using image histogram properties.

The results of any adjustments you make will not be remembered until you save your photograph.

The Image Editor to Process Auto Color Corrections¶

Black and White Conversions ¶

Black and White photography has always been fascinating in its abstraction capability. With the advent of digital photography, Black and White has almost become a desktop activity, as color images can be easily converted on the computer into black and white, even providing a set of vintage film roll profiles. This filter is also able to simulates traditional infrared film material.

Legacy Films Emulation ¶

digiKam comes with a couple of black & white filters that you can use on your photographs. Under the Color ‣ Black & White… menu you will find classic black & white chemical toning used in analog photography. The controls come on four drop-down items: Film, Lens Filters, Tone and Luminosity as shown on the screenshot below. Film, filters and color toning can be applied independently of each other (on top of each other). The filters actually influence the RGB channel mixing, whereas the toning purely adds a uniform monochromatic tint to the black & white photograph. In the lightness tab you will find a tonal adjustment tool (like curve adjust), a contrast tool and an over-exposure indicator to improve the Black and White rendering.

The Image Editor to Emulate Black and White Films¶

With Film setting, a specific settings allows to emulate a number of famous Black and White photographic films as:

Generic.

Agfa: 200X, Pan 25, Pan 100, Pan 400.

Ilford: Delta 100, Delta 400, Delta 400 Pro 3200, FP4 Plus, HP5 Plus, PanF Plus, XP2 Super.

Kodak: Tmax 100, Tmax 400, TriX.

With Lens Filters setting, a color filter can be simulated as placed on front of lens:

No Lens Filter: simulate black & white neutral film exposure.

Green Filter: simulates black & white film exposure with green lens filter. This comes good with all scenic images, especially suited for portraits taken against the sky (similar to 004 Cokin(tm) Green filter).

Orange Filter: simulates black & white film exposure with an orange lens filter. This will enhance landscapes, marine scenes and aerial photography (similar to 002 Cokin(tm) Orange filter).

Red Filter: simulates black & white film exposure with red lens filter. Creates dramatic sky effects and can simulate moonlight scenes in daytime (similar to 003 Cokin(tm) Red filter).

Yellow Filter: simulates black & white film exposure with yellow lens filter. Most natural tonal correction, improves contrast. Ideal for landscapes (similar to 001 Cokin(tm) Yellow filter).

With Tone setting, a color tint can be applied to the image:

Sepia Filter: gives a warm highlight and mid-tone while adding a bit of coolness to the shadows - very similar to the process of bleaching a print and re-developing in a sepia toner (typical for your grandmothers photographs). Similar to 005 Cokin(tm) Sepia filter.

Brown Filter: similar to Sepia Tone filter, but less pronounced.

Cold Filter: start subtle and replicate printing on a cold tone black & white paper such as a bromide enlarging paper.

Selenium Filter: effect that replicates traditional selenium chemical toning done in the darkroom.

Platinum Filter: effect that replicates traditional platinum chemical toning done in the darkroom.

Simulate Infrared Film ¶

Simulating classical infrared film material (the effect is rendered in black and white) is an interesting alienation effect that is even stronger and more dramatic than pure black and white conversion. Contrast and an abstract touch are improved, which can underpin the expression of the photographer as an artist. It is like taking an image in black and white with a red filter on the camera lense. Areas which reflect little red light, e.g. the sky, will show as low density, dark areas. Areas which are excellent reflectors of red light, e.g. most green foliage, will be high density areas. And snow landscapes are really dramatic.

The Image Editor to Emulate Infrared Films¶

The filter tries to reproduce the famous Ilford(tm) SFX and Kodak Tmax infrared film series. These films has a sensitivity range of 200-800 ISO:

Ilford: SPX 200, SPX 400, SPX 800.

Kodak: HIE.

备注

Because the filter mixes color channels to reproduce infrared film (with emphasis on green channel), one can not simulate infrared effect from Black and White original photograph, since the color information is missing.

Inverting Colors ¶

In case of digitalize analog film with a scanner, color can appear inverted compared to the reality. This tool allows to reverse the colors into their respective complementary colors.

Invert color to a complementary color (or opposite color of color on the color wheel), consist to have cyan as the opposite color of red, yellow as opposite color for blue, and magenta as the opposite color of green. With Color ‣ Invert option, we can invert all the pixel colors and brightness values in the image, as if the image was converted into a negative. Dark areas become bright and bright areas become dark. Hues are replaced by their complementary colors.

Simulate Negative Film ¶

While digiKam is first and foremost an application for processing and organizing digital photos, it also features tools for working with film negatives.

Before you can process negatives in digiKam, you need to digitize them. If you don’t have access to a film scanner or a lab that offers film scanning services, you can digitize film using a DSLR camera (there are plenty of tutorials on how to do that on the Web, as this one). The rest of the process assumes that you are using the latter way to digitize film negatives.

Open a RAW file containing a film negative in the editor. Crop the original file and apply lens correction if necessary. Choose then Color ‣ Invert to transform the negative into a positive image. In case you work with the color negative, the converted image most likely requires some additional tweaking. First of all, the converted image is likely to have a strong blue tint. The easiest way to remove it is to use digiKam’s Auto-Correction tool. Choose Color ‣ Auto-Correction and select one of the presets. In many cases, the Auto Levels or Equalize presets do a decent job of correcting the colors. If the colors still look slightly off, you can adjust them further using the Colors ‣ Color Balance tool.

The Image Editor Tool to Simulate Negative Film¶

The Invert feature in combination with an Auto-Correction preset provides a quick-and-dirty way of converting negatives, but digiKam has another tool designed specifically for processing color negatives. To access it, choose the Color ‣ Color Negative menu entry. The Color Negative Film interface contains several handy features that can help you to convert the negative and tweak the resulting image. While the Invert tool uses a generic profile for converting negatives, the Color Negative Film interface offers profiles for many popular film types. So the first step is to select the appropriate profile. For better results, try to enable the Color Balance option, too. If the used film is not in the list, you can use the Neutral profile as a fall back.

Although choosing the matching film profile may yield a better result, the converted image may still require some work. In most cases, you may need to adjust the white point to remove the remaining blue tint. You can do this either manually or automatically using the appropriate tools. Usually, the automatic white point adjustment does the job, but the resulting image needs to be brightened up by adjusting the Exposure and the Gamma sliders.

Colors Balance ¶

Digital cameras often have problems with lighting conditions and it is not unusual to want to correct the color contrast and brightness of a photograph. You can experiment with altering the levels of different aspects of your photographs using the tools under the Color menu. You can see any adjustments you make reflected in the preview. When you are happy with the results, press Ok and they will take effect.

If your image is washed out (which can easily happen when you take images in bright light) try the Hue/Saturation/Lightness tool, which gives you four sliders to manipulate, for Hue, Saturation, Vibrance, and Lightness. Raising the saturation will probably make the image look better. In some cases, it is useful to adjust the lightness at the same time. Lightness here is similar to Brightness in the Brightness/Contrast/Gamma tool, except that they are formed from different combinations of the red, green, and blue channels.

When you take images in low light conditions, you could get the opposite problem: too much saturation. In this case the Hue/Saturation/Lightness tool is again a good one to use, only by reducing the saturation instead of increasing it. You can see any adjustments you make reflected in the preview image. When you are happy with the results, press Ok and they will take effect.

Adjust Curves ¶

The digiKam Adjust Curves is a tool to non-linearly adjust luminosity graduation and color channels.

The Adjust Curves tool is the most sophisticated tool available to adjust the images’ tonality. Start it from the Color ‣ Curves Adjust… Image Editor menu. It allows you to click and drag control points on a curve to create a free function mapping input brightness levels to output brightness levels. The Adjust Curves tool can replicate any effect you can achieve with Brightness/Contrast/Gamma or the Adjust Levels tool, though it is more powerful than either one of them. But this tool can do more for you, it helps you to improve the tonal quality of your photographs to very finely stepped gray scales. And do not forget that the better the photographs are (good exposure, lossless format, 24 or 32 bit deep) the more you can improve them. Navigate to the “Achieving ultimate tonal quality” section of this instructive page: Tonal quality and dynamic range in digital cameras by Norman Koren. Use Adjust Curves tool to do just the same.

This tool provides visual curves to modify the intensity values of the active layer displayed as a histogram non-linearily. In Curve smooth mode, you change the curves shape by adding new points to the curve or by moving end point positions. Another way, is to draw all the curve manually in Curve free mode. In both cases the effect is immediately displayed in the image preview area to the left, where the preview can be configured by clicking on the top left icons.

To the left, half of the original and the target preview image is shown. The target preview is updated dynamically according to the widget settings. On the right side the following options are available:

Modify Channel: with this combo box you can select the specific channel to be modified by the tool:

Luminosity: changes the intensity of all pixels.

Red: changes the Red saturation of all pixels.

Green: changes the Green saturation of all pixels .

Blue: changes the Blue saturation of all pixels.

Alpha: changes the transparency of all pixels.

Next to this box are two icons to select Linear or Logarithmic Histogram display. For images taken with a digital camera the linear mode is usually the most useful. However, for images containing substantial areas of constant color, a linear histogram will often be dominated by a single bar. In this case a logarithmic histogram will be more appropriate.

Main Curves Editing Area: the horizontal bar (x-axis) represents input values (they are value levels from 0 to 255). The vertical bar (y-axis) is only a scale for output colors of the selected channel. The control curve is drawn on a grid and crosses the histogram diagonally. The pointer x/y position is permanently displayed above the grid. If you click on the curve, a control point is created. You can move it to bend the curve. If you click outside the curve, a control point is also created, and the curve includes it automatically. So each point of the curve represents an ‘x’ translated into a ‘y’ output level.

Curve Type for channel: below the editing area are several icons that determine whether the curve can be edited using Curve smooth mode or Curve free mode. Smooth mode constrains the curve type to a smooth line with tension and provides a realistic rendering. Free mode lets you draw your curve free-hand with the mouse. With curve segments scattered all over the grid, result will be surprising but hardly repeatable. A Reset to defaults button is also available. If, for example, you move a curve segment to the right, i.e. to highlights, you can see that these highlights are corresponding to darker output tones and that image pixels corresponding to this curve segment will go darker. With color channels, moving right will decrease saturation up to reaching complementary color. To delete all control points (apart from both end points), click on the Reset button. To delete only one point, move it onto another point. Just ply with the curves and watch the results. You even can solarize the image on part of its tonal range. This happens when the curve is inverted in some part. The original photo preview has a red marker on it. If you place this marker to a zone you want to modify, a corresponding line will be drawn on the curve grid indicating the original value. Create a point on that line and move it up or down to adjust it to your pleasing.

Save As and Load: these buttons are used to do just that. Any curves that you have set can be saved to the filesystem and loaded later. The used file format is The Gimp Curves format.

Reset: this button resets all curve values for all channels.

The curves tool has several features that facilitate the positioning of points on the control curves. Clicking the mouse button in the original image preview area produces a vertical doted bar in the graph area of the curves tool. The bar position corresponds to the pixel value the mouse cursor is over in the image window. Clicking and dragging the mouse button interactively updates the position of the vertical bar. In this way, it is possible to see where different pixel values in the image are located on the control curve and helps to discover the locations of shadow, midtone, and highlight pixels.

Using this way and the three Tone Color Picker buttons will automatically create control points on the curve in all channels for shadow, middle, and highlight tones. Enable the color picker button that you want to use, and click on the original image preview area to produce control points on each of the Red, Green, Blue, and Luminosity control curves.

Adjust Levels ¶

The digiKam Adjust Levels is a tool to manually adjust the histogram channels of an image.

Situated between the more sophisticated Adjust Curves tool and the simpler Brightness/Contrast/Gamma Image Editor tool is this Adjust Levels tool for improving exposure. Although the dialog for this tool looks very complicated, for the basic usage we have in mind here, the only part you need to deal with is the Input Levels area, concretely the three sliders that appear below the histogram.

This widget contains a visual graph of the intensity values of the active layer or selection (histogram). Below the graph are five sliders that can be clicked into and dragged to constrain and change the intensity level for the image. The left sliders position represents the dark areas and similarly, the right position represents the light areas.

Actually the easiest way to learn how to use it is to experiment by moving the three sliders around, and watching how the image is affected.

On the right, both an original and a target preview image is available. The target preview is updated dynamically according to the slider positions. On the left, the following options are available:

Modify levels for Channel: this combo box allows the selection of the specific channel that will be modified by the tool:

Luminosity: this option makes intensity changes against all pixels in the image.

Red: this option makes Red saturation changes against all pixels in the image.

Green: this option makes Green saturation changes against all pixels in the image.

Blue: this option makes Blue saturation changes against all pixels in the image.

Alpha: this option makes transparency changes against all pixels in the image.

Set Scale for channel: this combo controls whether the histogram will be displayed using a linear or logarithmic amplitude. For images taken with a digital camera, the linear mode is usually the most useful. However, for images that contain substantial areas of constant color a linear histogram will often be dominated by a single bar. In this case a logarithmic histogram will often be more useful.

Input Levels: the input levels allow manual adjustments to be selected for each of the ranges. The main area is a graphic representation of image dark, mid and light tones content. They are on abscissa from level 0 (black) to level 255 (white). Pixel number for a level is on ordinate axis. The curve surface represents all the pixels of the image for the selected channel (histogram). A well balanced image is an image with levels (tones) distributed all over the whole range. An image with a predominant blue color, for example, will produce a histogram shifted to the left in Green and Red channels, manifested by green and red color lacking on highlights. The level ranges can be modified in three ways:

Three sliders: the first on the top for Dark Tones*, the second one for **Light Tones*, and the last one on the bottom for **Midtones (often called Gamma value).

Three input boxes to enter values directly.

Three Color Picker buttons using the original photo preview to automatically adjust inputs levels settings for shadow, midtone and highlights. There is also a fully automated adjustment button available next to the reset button.

Output Levels: the output levels allow manual selection of a narrowed-down output level range. There are also two sliders located here that can be used to interactively change the output levels like Input Levels. This output level compression may, for example, be used to create a bleached image as a background for some other subject to put into the foreground.

Auto: this button performs an automatic setting of the levels based on the pixel intensities of the image.

Save As and Load: these buttons are used to do just that. Any Levels that you have set can be saved to the filesystem and loaded later. The used file format is compatible with The Gimp Levels format.

Reset All: this button reset all Input Levels and Output Levels values for all channels.

The Adjust Levels tool has several features to facilitate the positioning input levels sliders. Clicking the mouse button in the original image preview area produces a vertical doted bar in the graph area of the histogram. The bar position corresponds to the pixel value under the mouse cursor in the image window. Clicking and dragging the mouse button interactively updates the position of the vertical bar. In this way it is possible to see where different pixel values in the image are located on the input levels sliders and helps to discover the locations of shadow, midtone, and highlight pixels.

Using in this mode and the three Color Picker buttons will automatically adjust input levels settings in all channels for shadow, middle, and highlight tones. Enable the color picker button that you want use, and click on the original image preview area to set input levels on each of the Red, Green, Blue, and Luminosity histogram channels.

Over Exposure Indicator option checks all color channel to see if more than one channel in a pixel is over-exposed, and you will see the combined color resulting of channel level settings. This feature is available as an indicator in the target preview area and has no effect on final rendering.

Correcting Exposure ¶

The simplest tool to use is the Brightness/Contrast/Gamma tool. It is also the least powerful, but in many cases it does everything you need. This tool is often useful for images that are overexposed or underexposed; it is not useful for correcting color casts. The tool gives you three sliders to adjust, for Brightness, Contrast and Gamma. You can see any adjustments you make reflected in the preview image. When you are happy with the results, press Ok and they will take effect.

备注

Another important tool called Levels Adjust provides also an integrated way of seeing the results of adjusting multiple levels and also enables you to save level settings for application to multiple photographs. This can be useful if your camera or scanner often makes the same mistakes and you want to apply the same corrections. See the dedicated Adjust Levels manual for more information. See also a way of correcting exposure problems using the Adjust Curves tool.

Correcting Colors ¶

This tool is used to adjust hue, saturation, and lightness levels on a range of color weights for the current image. You can access the tool by the menu entry Color ‣ Hue/Saturation/Lightness

The tool settings are listed below:

A Hue / Saturation color map to select visually the respective primary color to adjust. Just move and click with the mouse to set Hue and Saturation values in sliders below the map.

Hue: The slider allow you to select a hue in the color circle (-180, 180).

Saturation: The slider allow you to select a saturation (-100, 100).

Vibrance: The slider allow you to adjust the vibrance of the image. Vibrance performs selective saturation on less saturated colors and avoiding skin tones.

Lightness: The slider allows you to select a luminosity value (-100, 100). Lightness changes here concern a color range, while they concern a color tone with Curves Adjust and Levels Adjust tools, which work on color channels. If you change the Red lightness with this tool, all red pixels will be changed. With Curves Adjust and Levels Adjust tools, only dark, bright, or medium pixels luminosity will be changed.

You can see any adjustments you make reflected in the preview image. When you are happy with the results, press Ok and they will take effect.

The Image Editor Tool Correcting Colors¶

Channel Mixer ¶

The digiKam image Channel Mixer is a tool to remix the color channels to improve or modify the photograph color shades.

The Channel Mixer is an another sophisticated tool to refine the images’ tonality. Start it from the Color ‣ Channel Mixer Image Editor menu.

With the channel combo box you select and display the histogram per color. It gives a first hint of how to correct the channels by their relative distribution and amplitude. The left half of the dialog window always shows a preview of what you are doing. The original for comparison can be seen when selecting its own window tab.

The target photo preview has a red marker available. If you place this marker somewhere in the image, a corresponding vertical bar will be drawn in the histogram indicating the color level value in the current channel selected.

Now the controls are to the lower right: Red, Green and Blue slider controls enable you to mix the channels. If you check Preserve Luminosity the image will retain its overall luminosity despite you changing its color components. This feature is particularly useful when you also ticked the Monochrome box. Because the channel mixer is the tool to make great Black and White conversions of your photographs. Try to reduce the green channel for Black and White portraits.

备注

Sometimes, especially when doing Monochrome mixing, reducing one color channel may increase visible noise, which actually originates in the chroma noise. Chroma noise means that the little noise specs do not appear at the same location in all the color channels, but the noise patterns looks different in every channel. If that is the case you can improve the monochrome conversion by reducing the chroma noise first.

Save As and Load buttons are used to do just that. Any mixer settings that you have set can be saved to the filesystem and loaded later. The used file format is The Gimp channel mixer format.

Over Exposure Indicator option adds up the colors if more than one channel in a pixel is over-exposed, and you will see the combined color resulting of channel gain settings. This rule is applying to target preview area and haven’t effect to final rendering.

Reset All button resets all channel mixer settings to default values.

White Balance ¶

The digiKam White Balance is a semi-automatic tool to adjust the white-balance of a photograph.

White Balance setting is a common hurdle for digital still cameras. In the ‘good old time’ of film rolls, the white balance was done by the photolab. Nowadays the poor little camera has to guess what is white and what is black. Most of the time, what the camera chooses as the white point, is not of the correct shade or hue. Using this tool it is easy to correct this problem. It provides a variety of parameters that can be trimmed to obtain a better result.

备注

Even if the White Balance correction is not limited to 8 bit per channel, if you depart too much from the original, over exposure zones may appear. If you can adjust the White Balance in RAW conversion mode, the margin for correction will be greater as it processes correction while demosaicing.

The preview window can be resized. To the left, both an original and a target preview tab is shown. The target preview is updated dynamically according to the tool’s settings. If you want to see the original White Balance, just click on that tab.

The target photo preview has a red marker available. The luminosity value of the pixel under the marker is shown as a vertical line in the histogram .

To the top right, the widget displays a histogram that is dynamically updated when changing the parameters. This histogram is very instructive as it shows that even in well exposed photos, most of the pixels have very small luminosity. With a button you can select to show either one of the 3 colors (or the sum of it which is called luminosity).

With Exposure you can digitally change the original photo exposure. Increasing the exposure is has the risk of making the pixel noise more visible and to blow out the highlights. Check the Over exposure indicator at the lower right to see if you run into saturation problems. The Black Point adjustment can be used to cut the histogram from the left. If your photograph looks foggy (histogram has empty space on the left, black side), you probably need to use this option. The Exposure and Black Point adjustments can be automatically estimated by pressing the Auto Exposure Adjustments button. This sets the black point quite accurately.

The contrast of your output depends on Shadows, Saturation, and Gamma parameters. The Shadows adjustment lets you enhance or diminish the shadow details in your photo.

Increasing the contrast of your photograph can have the side effect of reducing the apparent Saturation of the photo. Use a value larger than 1 to increase the saturation and a value of less than 1 to desaturate the photo. A value of 0 will give you a black and white photo. Don’t be shy to bump up the saturation of your photos a little. The general rule is that for higher Contrast (lower Gamma) you need to apply more Saturation.

The next set of options is the mainstay of White Balance settings, which controls the ratio between the three color channels. Here you can set the color Temperature, making your image warmer or colder. Higher temperature will result in a warmer tint. Setting the ratio between the three color channels requires two adjustments. Since the temperature adjustment mostly controls the ratio between the red and the blue channels, it is natural that the second adjustment will control the intensity of the Green channel.

Instead of fiddling around with the above controls, you can simply use the Temperature Tone Color Picker button. Press on this button and click anywhere on the original preview image to get the output color of that area to calculate the white color balance temperature settings. This way, Temperature and Green values are automatically computed.

In addition you can set the White Balance using the preset list. These are the white color balance temperature presets available:

Color Temperature	Description	Kelvin
40W	40 Watt incandescent lamp.	2680
200W	200 Watt incandescent lamp, studio lights, photo floods.	3000
Sunrise	Sunrise or sunset light.	3200
Tungsten	Tungsten lamp or light at 1 hour from dusk or dawn.	3400
Neutral	Neutral color temperature.	4750
Xenon	Xenon lamp or light arc.	5000
Sun	Sunny daylight around noon.	5500
Flash	Electronic photo flash.	5600
Sky	Overcast sky light.	6500

Color Temperature is a simplified way to characterize the spectral properties of a light source. While in reality the color of light is determined by how much each point on the spectral curve contributes to its output, the result can still be summarized on a linear scale. This value is useful e.g. for determining the correct white balance in digital photography, and for specifying the right light source types in architectural lighting design. Note, however, that light sources of the same color (metamers) can vary widely in the quality of light emitted.

Low Color Temperature implies more yellow-red light while high color temperature implies more blue light. Daylight has a rather low color temperature near dawn, and a higher one during the day. Therefore it can be useful to install an electrical lighting system that can supply cooler light to supplement daylight when needed, and fill in with warmer light at night. This also correlates with human feelings towards the warm colors of light coming from candles or an open fireplace at night. Standard unit for color temperature is Kelvin (K).

Over Exposure Indicator option adds up the colors if more than one channel in a pixel is over-exposed, and you will see the combined color resulting of White Color Balance controls settings. This rule is applied to target preview area as an indication only and has no effect on the final rendering.

Save As and Load buttons are used to do just that. Any White Color Balance settings that you have set can be saved to the filesystem in a text file and loaded later.

Reset All button resets all filter settings to default values corresponding to Neutral White Balance color. Attention, even the neutral setting might be different from your original photograph. If you save it, the white balance will be changed.