The bits per pixel (BPP) of an image represents the number of bits used to represent each pixel, determining the color depth and the amount of information stored for each pixel. You can find the bits per pixel by dividing the total number of bits representing the image's color data by the total number of pixels in the image.
Calculating Bits Per Pixel (BPP)
Here's a breakdown of how to calculate BPP:
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Determine the Total Embedding Size (Total Bits): This refers to the total number of bits used to store the image's color information. This might require knowing the file size and subtracting any header information.
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Calculate the Number of Pixels: Multiply the image's width (in pixels) by its height (in pixels). This gives you the total number of pixels in the image.
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Calculate BPP: Divide the total embedding size (in bits) by the total number of pixels.
- Formula:
BPP = Total Bits / Total Pixels
- Formula:
Example
Let's say you have an image with the following characteristics:
- Width: 640 pixels
- Height: 480 pixels
- Total Embedding Size: 7,372,800 bits
Here's how you would calculate the BPP:
- Total Pixels: 640 pixels * 480 pixels = 307,200 pixels
- BPP: 7,372,800 bits / 307,200 pixels = 24 bits per pixel
Therefore, this image has a BPP of 24, which often indicates a true-color image (using 24 bits to represent each pixel's color).
Understanding BPP Values
Different BPP values correspond to different color depths:
| BPP | Color Depth | Description |
|---|---|---|
| 1 | 2 colors | Black and white (monochrome) |
| 4 | 16 colors | Older systems, limited color palette |
| 8 | 256 colors | Grayscale or indexed color |
| 16 | 65,536 colors | High color, often uses 5 bits for red, 6 bits for green, and 5 bits for blue. |
| 24 | 16,777,216 colors | True color, uses 8 bits for red, 8 bits for green, and 8 bits for blue (RGB). |
| 32 | 16,777,216 colors + Alpha | True color with an alpha channel for transparency (RGBA). The extra 8 bits are for the alpha channel. |
Determining Total Bits
In practice, determining the "total bits" can be tricky because image file sizes include header information and possibly compression. If you know the image is uncompressed, then you can calculate total bits from the file size (multiply the file size in bytes by 8 to get bits). For compressed images, this calculation will be an approximation. Furthermore, some image formats, like indexed color images, use a color palette. The "total bits" then reflect the palette size and the number of bits per pixel used to index into the palette.
