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Camera Focus mechanism: Phase VS Contrast. 指導教授:梁肇文 教授 組 別:第 C 組 組員名單: 982006017 余謙 982006019 邱繼群 982006020 李京樺. Outline. Introduction The history of the autofocus system Contrast autofocus system Phase autofocus system Phase VS Contrast Prospect Reference. Introduction

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camera focus mechanism phase vs contrast

Camera Focus mechanism:Phase VS Contrast

指導教授:梁肇文 教授

組 別:第C組

組員名單:982006017余謙

982006019 邱繼群

982006020 李京樺

outline
Outline

Introduction

The history of the autofocus system

Contrast autofocus system

Phase autofocus system

Phase VS Contrast

Prospect

Reference

slide3
Introduction

The history of the autofocus system

Contrast autofocus system

Phase autofocus system

Phase VS Contrast

Prospect

Reference

introduction
Introduction

什麼是 “AF”系統

基本原理

主動式對焦原理

被動式對焦原理

slide5

什麼是 “AF”系統

  • 自動對焦又稱AF (Automatic Focus) 
  • 指相機以特定區域(一般指中央,但現在的系統已經可以指定在觀景窗內看到的任何一點角落),進行測距、進而調整鏡頭中鏡片形成焦點,使照相機內的影像看起來清晰之設計
slide6
基本原理
  • 基本原理
  • 用相機上的光電傳感器將物體發射或反射的光接受,根據相機內部晶片的計算與處理,最後由電動對焦裝置對焦
slide7

主動式對焦原理

  • 主動式:發射紅外線、超聲波,然後接受反射回來的訊號,測量來回的信號時間差,從而得到正確的距離參數。
  • 種類:聲波式、光學式
  • 優點:可以用於細線條物體和動體,也可以在低反差,弱光下對焦。
slide10

光學式

紅外線旋轉照射法

slide11

被動式對焦原理

  • 被動式: 接受景物自身的發光或反光。

包含:對比檢測及相位檢測對焦

  • 優點:不需要發射系統,耗能小,易小型化。可以在逆光下或透過玻璃對焦。
slide12
Introduction

The history of the autofocus system

Contrast autofocus system

Phase autofocus system

Phase VS Contrast

Prospect

Reference

slide14
Introduction

The history of the autofocus system

Contrast autofocus system

Phase autofocus system

Phase VS Contrast

Prospect

Reference

slide15

Contrast focus mechanism

  • Contrast focus mechanism(對比檢測 AF) 是什麼?

對比檢測自動對焦系統的原理是根據焦點處畫面的對比度變化,尋找對比度最大時的鏡頭位置,也就是準確對焦的位置。

slide16

如果對焦點是圖中的紅框,在影像上的分析,放大來看,在未完成對焦前(out of focus),框框內的像素與對比的關係就會變得差異很小(反差小);

  • 圖中的下圖是當對到焦時(in focus),框框內的像素(pixel)對比高。
slide17
隨著對焦鏡片開始移動,

畫面逐漸清晰,對比度開

始上升;當畫面最清晰,

對比度最高時,其實已處

於合焦狀態。

http://graphics.stanford.edu/courses/cs178/applets/autofocusCD.html

如同登山曲線

對比度

slide18
優點vs缺點

優點:

1.成本低,被廣泛運用

2.被攝對象反差較大時,相機仍可以準確地完成對焦工作。

缺點:

1.在微光環境下的對焦性能受到了很大的限制。

2.被攝對象反差較低時難以完成對焦。

slide19
Introduction
  • The history of the autofocus system
  • Contrast autofocus system
  • Phase autofocus system
  • Phase VS Contrast
  • Prospect
  • Reference
phase autofocus system
Phase autofocus system
  • Abstract
  • What is “phase” mean here?
  • Principle
  • Simple animation
  • Real structure
  • Autofocus process
  • Which System Camera Has?
  • Buying Tip
slide23

Δψ=k*Δx

Ι

Δψ

E

slide25

焦後

焦上

焦前

References:Camera technology : the dark side of the lens / Norman Goldberg(1992)

slide27

References:http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.htmlReferences:http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.html

slide29

Nikon F4

References:http://graphics.stanford.edu/courses/cs178/applets/slr-light-paths.jpg)

slide30

Nikon F4

References:http://graphics.stanford.edu/courses/cs178/applets/slr-light-paths.jpg)

slide31

Nikon F4

References:Camera technology : the dark side of the lens / Norman Goldberg(1992)

slide32

212B

212C

212A

85B

83B

85

85C

83

81

73

83C

73C

85A

73B

81C

75B

83A

75C

81A

81B

73A

75A

75

77A

77C

78C

77B

78A

References: United States Patent, Iwamoto. Patent Number:6,115,553. Sep.5,2000.

slide33

Canon EOS-1D

References: Canon 相機型錄.

slide35

References: United States Patent, Nakahara. Patent Number:7,058,294 B1. Jun.6,2006.

slide36

References: United States Patent, Nakahara. Patent Number:7,058,294 B1. Jun.6,2006.

slide37

References: United States Patent, Nakahara. Patent Number:7,058,294 B1. Jun.6,2006.

slide38

References: United States Patent, Nakahara. Patent Number:7,058,294 B1. Jun.6,2006.

slide39

References: United States Patent, Nakahara. Patent Number:7,058,294 B1. Jun.6,2006.

slide42
Introduction

The history of the autofocus system

Contrast autofocus system

Phase autofocus system

Phase VS Contrast

Prospect

Reference

slide44
比較主動和被動系統

『主動式』的優點

1.完全不受環境光線影響,也不會因為主體本身的反差條件而影響對焦操作,甚至能在黑暗的情況下工作。

『主動式』的缺點

1.不能透過玻璃工作

2.對具有吸收紅外線能力的主體也會得出不正確

的測距結果。

slide45
『被動式』的優點

1.活躍的自動對焦系統的準確度往往比被動系統

少得多。

『被動式』的缺點

1.當光線過暗或主體反差太低時是無法工作

2.對細線條的主體,對焦也較困難且精度不高

contrast vs phase
Contrast VS Phase比較
  • http://www.youtube.com/watch?v=UD9s5_nWTV4
slide47
Introduction

The history of the autofocus system

Contrast autofocus mechanism

Phase autofocus mechanism

Phase VS Contrast

Prospect

Reference

reference
http://graphics.stanford.edu/courses/cs178/applets/autofocusCD.htmlhttp://graphics.stanford.edu/courses/cs178/applets/autofocusCD.html

http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/5700/AUTO-FOCUS/Auto-Focus.html

http://www.sawfnews.com/Tech/67100.aspx

http://www.wretch.cc/blog/gaujei/7249826

http://graphics.stanford.edu/courses/cs178-10/applets/autofocusPD.html

影片:http://www.youtube.com/watch?v=UD9s5_nWTV4

http://www.sawfnews.com/Tech/67100.asp

Reference