What is a Megapixel?
A megapixel equals one million pixels and expresses the total raster resolution of an image or camera sensor. Pixel count indicates sampling capacity, but does not alone determine perceived image quality.
How Megapixels work
Megapixels summarize raster sample count by multiplying pixel width and height and expressing the result in millions. The same count can describe different aspect ratios, so it does not specify either dimension or suitability for a particular crop. Captured detail also depends on optics, focus, sensor sampling, noise, and image processing. In a workflow, pixel dimensions drive decode memory, resizing effort, rendition limits, and achievable print or display size.
Key facts
- A 4000×3000 raster contains 12 million pixels and is therefore described as 12 megapixels. Cropping it changes the count even when no resampling occurs.
- Many camera sensors record one filtered color measurement per photosite and reconstruct full-color pixels through demosaicing, so sensor count is not a direct measure of color detail.
- Compressed file size does not scale solely with megapixels. Codec, quality settings, bit depth, noise, and scene complexity can make equal-resolution images occupy very different space.
When Megapixels matter
Use megapixel counts to estimate memory, processing time, output dimensions, and transformation limits. Higher counts preserve more spatial detail but increase storage and compute requirements.