For professional video editors, why is using ProRES on an iPhone much better than regular video for changing colors and fixing the look?

Using ProRes on an iPhone is much better than regular video for changing colors and fixing the look because ProRes is a professional-grade video codec designed specifically for post-production, retaining significantly more visual information than the highly compressed standard video formats like HEVC or H.264 typically used by iPhones for general recording. Regular video codecs prioritize small file sizes for storage and sharing, achieving this through aggressive data compression that permanently discards much of the original image data. ProRes, by contrast, employs a much lighter, less destructive compression method, preserving critical information essential for color manipulation.

The primary technical advantages of ProRes for professional color grading and look fixing stem from three key areas: bit depth, chroma subsampling, and compression type.

First, ProRes typically records at a higher bit depth, commonly 10-bit, compared to the 8-bit depth of standard iPhone video. Bit depth refers to the number of color or tonal values available for each primary color channel (red, green, blue). In 8-bit video, each channel has 256 possible shades, totaling over 16 million colors. While this seems like a lot, it provides limited headroom for adjustment. When colors are significantly altered in 8-bit footage, the limited number of available shades can lead to an effect called 'banding' or 'posterization,' where smooth color gradients, such as a sky, break down into noticeable, distinct steps or blocks of color. In contrast, 10-bit ProRes offers 1024 shades per channel, resulting in over a billion possible colors. This vastly larger palette provides significantly more latitude, or flexibility, for colorists to make extreme adjustments without introducing banding or visual artifacts, ensuring smoother transitions and more natural-looking results.

Second, ProRes often uses a superior chroma subsampling scheme, typically 4:2:2, whereas standard iPhone video commonly uses 4:2:0. Chroma subsampling is a method of reducing the amount of color information in a video signal, as the human eye is more sensitive to changes in brightness (luminance) than to changes in color (chrominance). In a 4:2:0 scheme, for every four pixels, the full luminance information is kept, but color information is only recorded for two pixels horizontally and two pixels vertically, effectively discarding three-quarters of the color data. This significantly reduces file size but can lead to a loss of fine color detail and make aggressive color adjustments difficult. With 4:2:2 chroma subsampling, color information is recorded for every two pixels horizontally and every two lines vertically, meaning half the color data is kept. This preserves much more accurate color detail, which is crucial for precise color grading, allowing for more nuanced and accurate color shifts without muddying colors or creating unwanted color casts.

Third, ProRes utilizes an 'intra-frame' compression method, meaning each video frame is compressed and stored largely independently. This makes ProRes an 'intermediate codec' because it's designed to be a high-quality format that's easy for editing software to process without requiring massive computational power to decompress. Standard video codecs like HEVC and H.264, on the other hand, employ 'inter-frame' compression, which saves space by analyzing groups of frames and only storing the differences between them. While highly efficient for playback and storage, this inter-frame compression makes significant manipulation of individual frames much more challenging. When an editor tries to make substantial changes to color or exposure in heavily inter-frame compressed footage, the editing software often has to reconstruct frames from predicted data, which can lead to visible compression artifacts, macro-blocking, or a general breakdown of image quality. ProRes, by treating each frame more independently, allows for robust and artifact-free manipulation during the color grading process, ensuring that the original image integrity is maintained even after extensive adjustments.