Pixel data is typically stored linearly in a contiguous memory area, row by row. This means that the bitmap is essentially one long sequence of bytes representing the color values for each pixel.
Linear Storage Explained
Imagine a digital image as a grid. Each cell in the grid is a pixel. Linear storage represents these pixels as one long, unbroken line. The image's width determines how many pixels are in each row, and the height determines the number of rows.
- Rows are Sequential: Each row of pixels follows the previous row in memory.
- Contiguous Memory: All pixel data is stored in a single, unbroken block of memory.
- Consistent Row Length: Each row contains the same number of bytes. This is crucial for quickly calculating the memory address of any given pixel.
Example: A Small Grayscale Image
Let's say we have a grayscale image that is 3 pixels wide and 2 pixels high. Each pixel's grayscale value is represented by a single byte (0-255). The data might be stored as follows:
Row 1: [Pixel 1 Value] [Pixel 2 Value] [Pixel 3 Value]
Row 2: [Pixel 1 Value] [Pixel 2 Value] [Pixel 3 Value]In memory, this would be one continuous sequence:
[Pixel 1 Value] [Pixel 2 Value] [Pixel 3 Value] [Pixel 1 Value] [Pixel 2 Value] [Pixel 3 Value]
Color Images (RGB)
For color images, each pixel typically requires multiple bytes to represent the red, green, and blue components. For example, in a 24-bit RGB image, each pixel requires 3 bytes (one for red, one for green, and one for blue). So the storage would become:
Row 1: [Red1][Green1][Blue1] [Red2][Green2][Blue2] [Red3][Green3][Blue3]
Row 2: [Red1][Green1][Blue1] [Red2][Green2][Blue2] [Red3][Green3][Blue3]Calculating Pixel Address
Knowing that the data is stored linearly, you can easily calculate the memory address of any specific pixel. The formula depends on the image's pixel format (bytes per pixel) and dimensions (width and height).
Address = (y * row_width_in_bytes) + (x * bytes_per_pixel)
Where:
yis the row number (starting from 0)xis the column number (starting from 0)row_width_in_bytesis the number of bytes in each row (image width * bytes per pixel)bytes_per_pixelis the number of bytes used to represent a single pixel (e.g., 3 for 24-bit RGB)
Implications of Linear Storage
- Efficiency: This linear arrangement is efficient for sequential access and processing.
- Address Calculation: It allows for quick address calculations for individual pixels.
- Format variations: Some formats may include padding at the end of each row to ensure memory alignment, impacting row_width_in_bytes calculations.
In summary, pixel data is predominantly stored linearly, allowing efficient access and manipulation of image data. The exact storage format depends on the color depth and image format.
