How do you calculate the file size of an image?

• A. File Size = Resolution × Number of Colors
• B. File Size = Resolution × Colour Depth
• C. File Size = Width × Height
• D. File Size = Resolution × Colour Depth

Answer: (D)

Images are stored as a grid of pixels, and each pixel uses a certain number of bits to represent its color. The total amount of data (the file size) depends on how many pixels there are and how many bits each pixel needs. If you know the total number of pixels (often called the resolution) and the colour depth (bits per pixel), you multiply them: total bits = pixel count × colour depth. Then you usually convert bits to bytes by dividing by 8.

So, for an uncompressed image, file size in bits is the resolution (pixels) times the colour depth (bits per pixel). If you plug in the numbers, you can then divide by 8 to get bytes, and further convert to kilobytes or megabytes as needed. For example, a 1920×1080 image (about 2,073,600 pixels) with 24-bit colour would be 2,073,600 × 24 = 49,766,400 bits, which is 6,220,800 bytes (about 5.93 MB).

In practice, many image formats use compression, so the actual file size can be smaller than this uncompressed estimate. The key idea the correct option captures is that the size comes from pixel count combined with how many bits each pixel uses.