A bitmap is represented in binary by encoding each pixel's color as a binary number and organizing these binary numbers in a grid-like structure.
Here's a breakdown of how this works:
Pixel Representation
- Pixels: Bitmap images are composed of a grid of pixels. Each pixel represents a single color at a specific location in the image.
- Color Encoding: Each distinct color within the image is assigned a unique binary number. The length of this binary number determines the number of colors that can be represented in the image. For example:
- 1-bit color (monochrome): Allows 2 colors (e.g., black and white), with '0' representing one color and '1' representing the other.
- 8-bit color (grayscale or indexed color): Allows 256 colors (28), with each color indexed by a binary number from 00000000 to 11111111.
- 24-bit color (True color): Allows 16,777,216 colors (224). Typically, 8 bits are assigned for each of the red, green, and blue (RGB) color components.
- 32-bit color: Usually consists of 24-bit color (RGB) with an additional 8 bits for the alpha channel (transparency).
Bitmap Structure
The binary representation of a bitmap file generally consists of two main parts: the header and the pixel data.
- Header: The header contains metadata about the image, such as:
- File type identification (e.g., a "magic number" to identify the file as a bitmap)
- Image width and height (in pixels)
- Color depth (bits per pixel)
- Image size
- Color palette (if the image uses indexed color)
- Pixel Data: This section contains the binary data that represents the color of each pixel in the image. The pixels are usually stored row by row, from left to right and top to bottom. Each pixel's color is represented by its corresponding binary code.
Example
Consider a simple 2x2 black and white bitmap:
| Pixel | Color | Binary Representation |
|---|---|---|
| (0,0) | Black | 0 |
| (1,0) | White | 1 |
| (0,1) | White | 1 |
| (1,1) | Black | 0 |
The pixel data might be represented in binary as: 0110
Implications
- File Size: Bitmap files can be large because they store the color information for each pixel individually. The larger the image and the greater the color depth, the larger the file size will be.
- Image Quality: Bitmap images can lose quality when scaled up because the pixels are simply enlarged, resulting in a blocky appearance.
- Examples of Bitmap Formats: BMP, PNG, TIFF, and JPEG (though JPEG uses lossy compression). Note that PNG supports both bitmap and indexed color modes.
In summary, a bitmap stores images as a grid of pixels, with each pixel's color represented by a binary number. These binary numbers are organized sequentially, along with header information, to create the complete image file.
