Panasonic AG-DVX200PJ Tech Brief - Volume 4 - Page 2

4:2:0 8-Bit Internal Recording and 4:2:2 10-Bit External Output Internally, the DVX200 records in many di erent frame sizes and recording formats (MP4, MOV, and AVCHD), but all the recordings share these properties: they're all quantized to 8-bit, and they all use 4:2:0 color subsampling. And while the DVX200 can't internally record 10-bit 4:2:2, it can output 10-bit 4:2:2 through its HDMI and SDI ports, so it's available to record externally. Why 4:2:0 8-Bit Internal? One of the primary design decisions regarding the DVX200 was to make it as a ordable as possible, not only to buy, but to use. In that context it was decided that the DVX200 should use inexpensive, non-proprietary SDXC memory cards. Additionally, long recording times are a priority; since the DVX200 may be used in a wide variety of recording environments and may be used for long-duration recordings (such as for events or speeches), it was determined that lower bandwidth recording would provide the best combination of long recording times and inexpensive recording media. Keeping the bitrate to 100 megabits per second (or lower) allows for over an hour of recording on a 64GB SDXC card, while ensuring rock-solid reliability. Understanding the need for limited bitrate, the next task was to engineer a codec that delivered good picture quality while meeting that bitrate expectation. Video compression nearly exclusively uses "lossy" technology; information is discarded to reduce the data rate, and priorities are balanced to maintain the best image quality while discarding the least-important information. 10-bit quantizing and 4:2:2 color sampling are both desirable elements to have, if all things were equal and a large bitrate were possible to suitably encode those aspects of the image. But within the context of the desire for long recording times on inexpensive media, it was determined that 8-bit 4:2:0 provides su cient image quality for many potential uses. Professional video has used 8-bit digital encoding for decades; all DVD and Blu-Ray discs are encoded as 8-bit 4:2:0; and all HDTV broadcasts are done in 8-bit 4:2:0. 8-bit 4:2:0 can look very good. 10-bit 4:2:2 provides even more information, but takes up substantially more space to record it, and for many recordings and many jobs, it's simply not necessary. ere are many jobs where 10-bit and/or 4:2:2, while nice, are not absolutely required (as evidenced by the massive body of work that's been recorded on 8-bit 4:2:0 cameras over the last twenty years). Some broadcasters and some jobs may require 10-bit or 4:2:2, but many don't, and for those that don't, the DVX200 provides inexpensive internal long-format record capability on commodity media cards. 4:2:2 10-Bit External Output 10-bit 4:2:2 recording, when given su cient bandwidth, produces images that are more detailed, and easier to color grade, and easier to chroma key, and easier to composite, than 8-bit 4:2:0 does. 10-bit 4:2:2 is superior to 8-bit 4:2:0 when it can be adequately recorded (meaning, when there is su cient bitrate available to a ord devoting the necessary bits to recording the additional information.) Recording 4K or UHD footage at 10-bit 4:2:2 in high-quality intraframe encod-