[ This article was first published in the June, 2007, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe. ]
ProRes is the new QuickTime codec Apple released with Final Cut Studio 2. The reason it needed to be invented was that none of the HD codecs currently shipping with QuickTime supported both small file size and 10-bit quality. You could get one or the other, but not both.
The reason 10-bit quality is important is illustrated in this simulated picture.
All shades of gray, and shades of a color, are represented by a numeric value. In 8-bit video, these values range from 0 – 255. In 10-bit video, these values range from 0 – 1023. In both cases, 0 represents the absence of something, either white or a color, while either 255 or 1023 represents the maximum amount of white, or a color.
Research has shown that an 8-bit gray scale is essentially sufficient to smoothly represent all the shades of gray our eye can perceive. However, 8-bit color shows banding, that is, clear divisions between different shades of color. I’ve simulated this in the lower portion of the illustration above.
To prevent banding, color needs to be stored in 10-bit files. This provides smaller differences between color values, which prevents banding, but at the expense of much larger files.
DV, DVCPRO-50, DVCPROHD, HDV, XDCAM — the formats that many of us use every day — are all 8-bit formats. This means that they will have a tendency to exhibit banding in saturated colors.
This problem is made worse as we start using Color for color correction. This is because Color needs to render your color corrections into video files as part of its final output process. If you output 8-bit video, you could easily inject banding into your final masters.
To solve these problems, ProRes allows you to store both SD and HD video using 10-bit values, but at file sizes up to 33% smaller than uncompressed SD files and 90% smaller than uncompressed HD files. This allows us to take advantage of the improved image quality 10-bit video offers, without totally overloading our hard drives with massive files.
Here are some general rules you can use:
Note: Frame rate and image size will impact file size, these estimates assume worst case. Apple indicates under “normal conditions” we should expect file sizes about 30% smaller than my numbers.
As video editors we are constantly balancing image quality with file size. With ProRes, we have another tool we can use to help us in this process. While no one codec meets all possible needs, ProRes deserves to be seriously considered.
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