The size of the file depends on many factors. These factors include, image resolution, file format, and file compression. The higher the image resolution the larger the file, all things being equal. Digital cameras use many different file formats. Many cameras can save images in more than one format depending on their purpose.
Some cameras use their own proprietary format to store images.
Using a proprietary format will usually require an extra step to convert the image into one of the common formats like JPEG or TIFF before the image can be used. TIFF and JPEG formats are very commonly used in digital cameras. They are both compressed formats. TIFF files are around one-third the size of the uncompressed image. JPEG files can be compressed at varying rates.