Introduction:
In a digital signal processor (DSP), the brightness of a pixel is determined by the luminance value. Luminance represents the intensity or brightness of a color and is an essential component in representing images and videos.

Explanation:
Luminance is a measure of the perceived brightness of a color and is primarily determined by the intensity of the light emitted or reflected by an object. In digital image processing, luminance refers to the representation of brightness levels in an image or video.

Key Points:

1. Luminance:
- Luminance represents the brightness of an image or video pixel.
- It is a measure of the intensity of light emitted or reflected by an object.
- Luminance values range from 0 (black) to 1 (white) in digital systems.
- It is often represented as a grayscale image, where each pixel's value corresponds to its brightness level.

2. Digital Signal Processor (DSP):
- A digital signal processor is a specialized microprocessor designed for processing digital signals, such as audio, video, or image data.
- DSPs are commonly used in various applications, including image and video processing, communications, and audio processing.
- In the context of image and video processing, DSPs are responsible for performing various operations, including color space conversion, filtering, and enhancement.

3. Brightness Representation:
- The brightness of a pixel in a digital signal processor is typically represented using the luminance component.
- Luminance is often calculated based on the RGB (Red, Green, Blue) color model by applying appropriate weightings to the color channels.
- The luminance value is then used to determine the brightness level of the pixel.

4. Other Options:
- The other options mentioned in the question, such as transparent, chrominance, and opaque, do not directly represent the brightness of a pixel in a digital signal processor.
- Transparency refers to the degree to which an object allows light to pass through, while opacity refers to the opposite.
- Chrominance represents the color information in an image or video, which is separate from the luminance component.

Conclusion:
In a digital signal processor, the brightness of a pixel is determined by the luminance value. Luminance represents the intensity or brightness of a color and is an important component in representing images and videos. Other options mentioned in the question, such as transparent, chrominance, and opaque, do not directly represent the brightness of a pixel in a DSP.