Why does red eye removal make a file almost double in size?

Red eye removal often increases a file's size because the process involves altering pixel data significantly. The software typically replaces the red-eye pixels with new colors and may also apply smoothing or blending effects to achieve a natural look, resulting in more complex data. Additionally, if the image is saved in a format that uses lossless compression, the changes can lead to less efficient compression, further increasing the file size.