디스플레이 장치를 위한 고정 비율 압축 하드웨어 설계

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2016. 2. 이혁재.디스플레이 장치에서의 압축 방식은 일반적인 비디오 압축 표준과는 다른 몇 가지 특징이 있다. 첫째, 특수한 어플리케이션을 목표로 한다. 둘째, 압축 이득, 소비 전력, 실시간 처리 등을 위해 하드웨어 크기가 작고, 목표로 하는 압축률이 낮다. 셋째, 래스터 주사 순서에 적합해야 한다. 넷째, 프레임 메모리 크기를 제한시키거나 임의 접근을 하기 위하여 압축 단위당 목표 압축률을 실시간으로 정확히 맞출 수 있어야 한다. 본 논문에서는 이와 같은 특징을 만족시키는 세 가지 압축 알고리즘과 하드웨어 구조를 제안하도록 한다. LCD 오버드라이브를 위한 압축 방식으로는 BTC(block truncation coding) 기반의 압축 방식을 제안하도록 한다. 본 논문은 압축 이득을 증가시키기 위하여 목표 압축률 12에 대한 압축 방식을 제안하는데, 압축 효율을 향상시키기 위하여 크게 두 가지 방법을 이용한다. 첫 번째는 이웃하는 블록과의 공간적 연관성을 이용하여 비트를 절약하는 방법이다. 그리고 두 번째는 단순한 영역은 2×16 코딩 블록, 복잡한 영역은 2×8 코딩 블록을 이용하는 방법이다. 2×8 코딩 블록을 이용하는 경우 목표 압축률을 맞추기 위하여 첫 번째 방법으로 절약된 비트를 이용한다. 저비용 근접-무손실 프레임 메모리 압축을 위한 방식으로는 1D SPIHT(set partitioning in hierarchical trees) 기반의 압축 방식을 제안하도록 한다. SPIHT은 고정 목표 압축률을 맞추는데 매우 효과적인 압축 방식이다. 그러나 1D 형태인 1D SPIHT은 래스터 주사 순서에 적합함에도 관련 연구가 많이 진행되지 않았다. 본 논문은 1D SPIHT의 가장 큰 문제점인 속도 문제를 해결할 수 있는 하드웨어 구조를 제안한다. 이를 위해 1D SPIHT 알고리즘은 병렬성을 이용할 수 있는 형태로 수정된다. 인코더의 경우 병렬 처리를 방해하는 의존 관계가 해결되고, 파이프라인 스케쥴링이 가능하게 된다. 디코더의 경우 병렬로 동작하는 각 패스가 디코딩할 비트스트림의 길이를 미리 예측할 수 있도록 알고리즘이 수정된다. 고충실도(high-fidelity) RGBW 컬러 이미지 압축을 위한 방식으로는 예측 기반의 압축 방식을 제안하도록 한다. 제안 예측 방식은 두 단계의 차분 과정으로 구성된다. 첫 번째는 공간적 연관성을 이용하는 단계이고, 두 번째는 인터-컬러 연관성을 이용하는 단계이다. 코딩의 경우 압축 효율이 높은 VLC(variable length coding) 방식을 이용하도록 한다. 그러나 기존의 VLC 방식은 목표 압축률을 정확히 맞추는데 어려움이 있었으므로 본 논문에서는 Golomb-Rice 코딩을 기반으로 한 고정 길이 압축 방식을 제안하도록 한다. 제안 인코더는 프리-코더와 포스터-코더로 구성되어 있다. 프리-코더는 특정 상황에 대하여 실제 인코딩을 수행하고, 다른 모든 상황에 대한 예측 인코딩 정보를 계산하여 포스터-코더에 전달한다. 그리고 포스트-코더는 전달받은 정보를 이용하여 실제 비트스트림을 생성한다.제 1 장 서론 1 1.1 연구 배경 1 1.2 연구 내용 4 1.3 논문 구성 8 제 2 장 이전 연구 9 2.1 BTC 9 2.1.1 기본 BTC 알고리즘 9 2.1.2 컬러 이미지 압축을 위한 BTC 알고리즘 10 2.2 SPIHT 13 2.2.1 1D SPIHT 알고리즘 13 2.2.2 SPIHT 하드웨어 17 2.3 예측 기반 코딩 19 2.3.1 예측 방법 19 2.3.2 VLC 20 2.3.3 예측 기반 코딩 하드웨어 22 제 3 장 LCD 오버드라이브를 위한 BTC 24 3.1 제안 알고리즘 24 3.1.1 비트-절약 방법 25 3.1.2 블록 크기 선택 방법 29 3.1.3 알고리즘 요약 31 3.2 하드웨어 구조 33 3.2.1 프레임 메모리 인터페이스 34 3.2.2 인코더와 디코더의 구조 37 3.3 실험 결과 44 3.3.1 알고리즘 성능 44 3.3.2 하드웨어 구현 결과 49 제 4 장 저비용 근접-무손실 프레임 메모리 압축을 위한 고속 1D SPIHT 54 4.1 인코더 하드웨어 구조 54 4.1.1 의존 관계 분석 및 제안하는 파이프라인 스케쥴 54 4.1.2 분류 비트 재배치 57 4.2 디코더 하드웨어 구조 59 4.2.1 비트스트림의 시작 주소 계산 59 4.2.2 절반-패스 처리 방법 63 4.3 하드웨어 구현 65 4.4 실험 결과 73 제 5 장 고충실도 RGBW 컬러 이미지 압축을 위한 고정 압축비 VLC 81 5.1 제안 알고리즘 81 5.1.1 RGBW 인터-컬러 연관성을 이용한 예측 방식 82 5.1.2 고정 압축비를 위한 Golomb-Rice 코딩 85 5.1.3 알고리즘 요약 89 5.2 하드웨어 구조 90 5.2.1 인코더 구조 91 5.2.2 디코더 구조 95 5.3 실험 결과 101 5.3.1 알고리즘 실험 결과 101 5.3.2 하드웨어 구현 결과 107 제 6 장 압축 성능 및 하드웨어 크기 비교 분석 113 6.1 압축 성능 비교 113 6.2 하드웨어 크기 비교 120 제 7 장 결론 125 참고문헌 128 ABSTRACT 135Docto

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