[Foundation] Image Format Conversion in MATLAB: Conversion from RGB to Grayscale Image

# 2.1 RGB Image Model

### 2.1.1 RGB Color Space

The RGB (Red, Green, Blue) color space is an additive model that creates various colors by combining lights of different intensities in red, green, and blue. In the RGB color space, each pixel is represented by three channels corresponding to the intensity of red, green, and blue light.

### 2.1.2 Storage Format of RGB Images

RGB images are typically stored in the following formats:

- **BMP (Bitmap):** An uncompressed format where each pixel occupies 3 bytes (24 bits).
- **JPEG (Joint Photographic Experts Group):** A lossy compression format commonly used for storing photographs.
- **PNG (Portable Network Graphics):** A lossless compression format often used for storing images with transparency.
- **TIFF (Tagged Image File Format):** A flexible format that supports various compression algorithms and metadata.

# 2. The Theory of Image Format Conversion

Image format conversion is an important fundamental operation in image processing, involving transforming an image from one format into another. The theoretical basis of image format conversion mainly includes the RGB image model and the grayscale image model.

### 2.1 RGB Image Model

#### 2.1.1 RGB Color Space

The RGB color space is a three-primary color model composed of red (R), green (G), and blue (B) colors. In the RGB color space, any color can be represented by different combinations of these three primary colors.

#### 2.1.2 Storage Format of RGB Images

The storage format of RGB images is typically 24-bit, with each color component (R, G, B) occupying 8 bits. Therefore, each pixel point requires 24 bits for storage. The storage format of RGB images can be represented as:

[R1, G1, B1, R2, G2, B2, ..., Rn, Gn, Bn]

Where [R1, G1, B1] represents the color components of the first pixel point, [R2, G2, B2] represents the color components of the second pixel point, and so on.

### 2.2 Grayscale Image Model

#### 2.2.1 Grayscale Color Space

The grayscale color space is a single-channel color model that only contains luminance information. Each pixel point in a grayscale image is represented by a value ranging from 0 to 255, where 0 represents black, and 255 represents white.

#### 2.2.2 Storage Format of Grayscale Images

The storage format of grayscale images is typically 8-bit, meaning each pixel point requires 8 bits for storage. The storage format of grayscale images can be represented as:

[G1, G2, ..., Gn]

Where [G1] represents the luminance value of the first pixel point, [G2] represents the luminance value of the second pixel point, and so on.

# 3. Practical Conversion from RGB to Grayscale Images

### 3.1 Image Reading and Display in MATLAB

#### 3.1.1 imread() Function

The `imread()` function is used to read images from files. Its syntax is as follows:

I = imread(filename)

Where:

- `I`: The output image data, which is a three-dimensional matrix where the first two dimensions represent the rows and columns of the image, and the third dimension represents the number of image channels.
- `filen