DSC

/ˌdiː ɛs ˈsiː/

n. "VESA's visually lossless video compression enabling 8K@60Hz over DisplayPort HBR3 bandwidth limits."

DSC, short for Display Stream Compression, is a low-latency compression algorithm developed by VESA that achieves 3:1 ratios using DPCM prediction, YCoCg-R color transform, and entropy coding on pixel slices, enabling 4K@144Hz/8K@60Hz over existing DisplayPort 1.4 (25.92Gbps) and HDMI 2.1 links without perceptible artifacts. Processes frames in real-time (sub-microsecond latency) by dividing into independent slices (1/3-1/4 frame width), quantizing residuals after intra prediction—mandatory for USB4 UHBR20 tunnels exceeding raw pixel clocks.

Key characteristics of DSC include: Visually Lossless 3:1 compression (119Gbps 8K@60 → 40Gbps) imperceptible at normal viewing distances; Zero Latency real-time encoding/decoding (<1μs end-to-end); Slice-Based parallel processing of 1/3 frame widths with independent headers; YCoCg-R Color optimal for luma/chroma separation unlike RGB quantization; Rate Control maintains constant bitrate via qp adjustment without buffering.

Conceptual example of DSC usage:

/* DSC 1.2a encoder slice processing */
typedef struct {
    uint32_t slice_width;    // 1/3 frame width (e.g. 1280 for 3840x2160)
    uint32_t slice_height;   // 8-108 lines
    int qp;                  // Quantization parameter [8-17]
    bool intra_mode;         // Force all-intra slice
} dsc_slice_config;

void dsc_encode_slice(uint16_t *rgb_pixels, uint8_t *compressed) {
    // 1. YCoCg-R color transform
    int16_t y, co, cg, r;
    y  = (rgb >> 2) + (rgb >> 1) + (rgb >> 2); [youtube](https://www.youtube.com)
    co = (rgb >> 1) - (rgb >> 1);
    cg = (rgb >> 1) - (rgb >> 2); [youtube](https://www.youtube.com)
    
    // 2. DPCM prediction (left/above neighbors)
    int16_t pred_y = prev_y + left_y >> 1;
    int16_t res_y  = y - pred_y;
    
    // 3. Quantize + Huffman code
    uint8_t quant_y = res_y >> qp;
    huffman_encode(quant_y, compressed++);
    
    // 4. Repeat for Co/Cg, rate control
}

Conceptually, DSC shrinks raw pixel streams by predicting/chroma-subsampling within DisplayPort main stream attributes (MSA), enabling 4K@240Hz over DVI-era cables—slice headers negotiate compression ratio during link training alongside CTLE equalization. Decoder mirrors process instantly; gaming monitors auto-enable for VRR compatibility, stress-tested via PRBS patterns ensuring LFSR-generated video maintains 1e-12 BER through compressed pipeline.