What is the technical reason for the increased file size of ProRAW images compared to JPEGs, and how does this relate to their post-processing flexibility?

The increased file size of ProRAW images compared to JPEGs stems from fundamental differences in how image data is captured, processed, and stored. A JPEG file is an image that has undergone significant in-camera processing and lossy compression. Lossy compression means that permanent information is discarded to reduce file size. JPEGs typically store 8 bits of color information per color channel, meaning 256 distinct tonal values for red, green, and blue. During capture, the camera applies fixed settings for white balance, sharpening, noise reduction, and tone mapping directly to the image data, baking these adjustments into the final file. This results in a smaller file size because much of the original sensor data is discarded, and the remaining data is aggressively compressed. This process also limits post-processing flexibility because many decisions have been made irreversibly by the camera, making it difficult to recover details in blown-out highlights or deep shadows, or to make significant color shifts without introducing visual artifacts like banding. ProRAW, on the other hand, is Apple's proprietary RAW format that combines the benefits of a standard RAW image with computational photography. It stores much more of the original sensor data, which is the raw light information captured by the camera's sensor before significant processing. ProRAW typically captures 10 or 12 bits of color information per color channel, offering thousands of distinct tonal values (10-bit provides 1024 tones, 12-bit provides 4096 tones) compared to JPEG's 256. This higher bit depth significantly increases the amount of color and tonal information stored. Crucially, ProRAW also incorporates metadata and data from Apple's computational photography pipeline, such as Smart HDR, Deep Fusion, and Night Mode, but instead of applying these processes destructively, it preserves the underlying data and allows for non-destructive adjustment of their effects. While some minimal or lossless compression may be applied, it does not discard essential image information like JPEG does. The camera does not permanently bake in white balance, sharpening, noise reduction, or tone mapping into the core pixel data; instead, these adjustments are either stored as modifiable instructions or the data is preserved for user control. This preservation of extensive original sensor data, higher bit depth, and computational photography data without destructive compression directly leads to a significantly larger file size. This larger file size directly correlates to increased post-processing flexibility. With ProRAW, adjustments to exposure, white balance, shadows, highlights, contrast, sharpening, and noise reduction can be made non-destructively, meaning the original pixel data is preserved and edits are applied as instructions that can be altered or reverted at any time. The greater bit depth and preserved sensor data allow for substantial recovery of detail in underexposed shadows or overexposed highlights, providing a much wider dynamic range to work with compared to JPEG. Photographers can precisely fine-tune colors and white balance without introducing banding or other artifacts due to the abundance of tonal information. Furthermore, the integration of computational photography data allows users to modify or even undo the intensity of computational effects, such as the tone mapping of Smart HDR, giving unprecedented control over the final look that is impossible with a standard JPEG.