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What is white balance in image processing

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White balance (WB) is a key concept in image processing and photography. It ensures that photos or videos shot under different lighting sources accurately reproduce white, ensuring natural-looking colors.

Different lighting conditions produce different color temperatures. For example, daylight, fluorescent lighting, and incandescent lighting can all impart a bluish, greenish, or yellowish tint to photos.

Adjusting white balance corrects these color shifts, ensuring that the colors of objects appear as close to their true colors under neutral daylight as possible under various lighting conditions.

Most modern digital cameras offer an automatic white balance (AWB) feature, which automatically adjusts to produce accurate colors based on the scene. Users can also manually set white balance, selecting preset values (such as Sunlight, Cloudy, Shade, Tungsten, and Fluorescent) or customizing a custom color temperature.

Image editing software also typically provides tools for adjusting white balance in post-processing, allowing users to perform more precise color corrections on photos after capture.

Using white balance correctly is crucial for producing professional-quality images, especially in situations where accurate color reproduction is crucial, such as product photography and portraiture.

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White balance is a key technique in image processing used to correct image color deviations. Its core purpose is to eliminate color casts caused by differences in light source color temperature (e.g., a bluish cast under cool light and a yellowish cast under warm light). By adjusting the intensity ratios of the three RGB channels (red, green, and blue) of white objects in an image, it restores the image to a neutral white, thereby ensuring that other colors accurately represent the scene.

This technique is based on the human eye's constant perception of white and mimics the brain's ability to automatically correct color. Common algorithms include the grayscale world assumption (assuming the image is neutral gray on average), the perfect reflection method (using the brightest point in the image as a reference for white), and the dynamic threshold method.

White balance is typically performed during image preprocessing and is a core function of digital cameras, mobile phones, and video surveillance devices, directly impacting image quality and visual comfort.

If uncorrected, cool light sources (such as cloudy days) can cause images to have a bluish cast, while hot light sources (such as incandescent lamps) can cause them to have a reddish-orange cast. White balance effectively addresses these issues through color balancing algorithms, enhancing image authenticity and visual appeal.

by (106k points)
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In image processing, white balance (WB) is a key technique for correcting color shifts in images. Its core goal is to ensure that white objects in an image appear true white under varying light sources, while also ensuring that other colors appear natural and accurate. The following is a detailed explanation:

1. Why is white balance necessary?

Differences in light source color temperature: Different light sources (such as sunlight, incandescent light, fluorescent light, and LED light) have varying color temperatures, which can cause image color shifts. For example:

Warm light (low color temperature, such as candlelight) produces an overall yellowish/orange tint in the image.

Cold light (high color temperature, such as a cloudy day) produces an overall bluish tint in the image.

Differences between the human eye and a camera: The human eye automatically adapts to changes in light source, but camera sensors faithfully record the color of light, resulting in color distortion in uncorrected images.

2. How white balance works

White balance compensates for color temperature shifts in the light source by adjusting the gain of the red (R), green (G), and blue (B) channels in the image, restoring the neutrality of white objects in the image (R=G=B). The specific steps include:

Estimating the light source color temperature: Identifying the current light source type (e.g., daylight, shade, tungsten light, etc.) through algorithms or manual settings.

Adjusting color channels: Increasing or decreasing the brightness of corresponding channels based on the direction of color temperature shift. For example:

Under warm light (yellowish), increase the blue channel gain and decrease the red channel gain.

Under cool light (bluish), increase the red channel gain and decrease the blue channel gain.

3. Common White Balance Methods

Auto White Balance (AWB):

The camera or software automatically calculates adjustment parameters by analyzing grayscale areas in the image (e.g., a hypothetical white object).

Advantages: Convenient and suitable for most scenes.

Disadvantages: May fail in complex lighting conditions or when a neutral color reference is lacking.

Preset White Balance Modes:

Preset parameters based on common light sources (e.g., daylight, cloudy, tungsten light, fluorescent light, etc.).

Users can manually select a mode based on the scene.

Manual White Balance (Custom White Balance):

Use a gray card or white object as a reference and let the camera record its color and generate correction parameters during the shot. Suitable for professional photography or extreme lighting conditions.

Post-production Adjustment:

Manually adjust the temperature and tint sliders using image processing software (such as Photoshop or Lightroom).

4. Applications of White Balance

Photography and Videography: Ensure the faithfulness of colors in human skin tones, natural landscapes, and other areas.

Computer Vision: Prevent color shift from affecting algorithm performance in tasks such as object detection and image classification.

Medical Imaging: Correct the color of images from endoscopes, microscopes, and other equipment to improve diagnostic accuracy.

5. Example Results

Uncorrected Image: Shot indoors under tungsten lighting, the image has a yellowish cast, with the white wall appearing orange.

Corrected Image: White balance adjustment restores the wall to a white color, resulting in a natural overall color.

Summary

White balance is a core technique in image processing that eliminates the effects of light source color temperature and restores true colors. Whether achieved through in-camera functionality or post-production software, proper use of white balance can significantly improve image quality, avoiding visual discomfort or misinterpretation caused by color casts.

by (37.5k points)

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