E-3 CMOS 確實的動態範圍? (第2頁)

clp
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11樓

2008-04-12 22:38

pankang wrote:
我到dpreview瞄了一下，確實看不到E3動態範圍的數據，有哪位大大知道嗎？

據我所知是 8.8 EV, 和D300一樣, 在此範圍內, 不過 D300比E-3涵蓋多一些高光範圍, E-3比 D300涵蓋多低光範圍, IMO, 高光區爆掉是很難救回來的, 也就說說D300若是用"數位化相機要向右邊曝光 1/3 or 2/3 這樣的準則化", 比較佔優勢, 當然E-3對於低光部分至佔些便宜的.

另外寬容度, 應該是指所謂光線和 sensor 訊號反應成線性的範圍, 若有錯請指教.

johnchak

johnchak
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12樓

2008-04-13 0:04

這些數據全部在Dpreview上複製出來的，給各位大大參考。

nebulaforest

nebulaforest
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13樓

2008-04-13 1:23

幫放一下比較圖，來源一樣是Dpreview

看來E-3在高光部分，比其他廠同等級相機，還是比較容易過曝

不過暗部細節倒是能多紀錄1/2~1EV左右

pankang

pankang
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42分

14樓

2008-04-13 2:15

johnchak wrote:
這些數據全部在Dpr...(恕刪)

謝謝。

不過，我在google上找了有關動態範圍dB值，和曝光的EV值的定義，找到成都大學一篇有關CCD傳感器的作用原理。

http://72.14.235.104/search?q=cache:-3-sR8zf680J:202.115.138.28/2005/sensor/study/study-8.asp+%E5%8B%95%E6%85%8B%E7%AF%84%E5%9C%8D%EF%BC%8CCCD%EF%BC%8Cev%E5%80%BC%EF%BC%8CdB%E5%80%BC&hl=zh-TW&ct=clnk&cd=14

另外看到一篇文章寫道

「動態範圍是電子學理論中的一個客觀指標，單位是dB，也可以換算為bit，換算方法是1bit=6dB」。

另外，有一篇「數碼相機全應用」如此解釋EV曝光值和動態範圍：

「曝光指膠捲或感測器吸收的進光量，它由鏡頭開啟的直徑大小（光圈）和膠捲或感測器的感光時間（快門速度）共同決定，而曝光的效率是由膠捲或感測器的感光度決定的。根據上述原理，我們可以推出曝光值（EV）由光圈、快門速度和感光度共同決定。我們把0EV定義為光圈為f/1，快門速度為1s，感光度（ISO）為100時的曝光量。每當感測器吸收的光量減半（例如光圈調小一級或快門調快一倍），曝光值EV就會增加1。例如，6EV中感測器吸收的進光量為5EV的一半。高EV值被用於明亮的環境，在這些環境中，膠捲或感測器只需吸收很少的光，否則照片就會過曝。」

「色調範圍(Tonal Range)：數碼相機的色調範圍指描述動態範圍的色調數目。動態範圍寬不一定色調範圍寬，動態範圍窄，色調範圍也不一定窄。

感測器的動態範圍和色調範圍：
感測器的動態範圍和色調範圍是息息相關的。如果一個感測器的動態範圍是1000:1，其AD轉換器最少有10位元，那麼它必定會有一個寬闊的色調範圍。一個擁有10位元AD轉換器的感測器能輸出大約1,000個不同的色調，當然感測器的動態範圍要不小於1000:1，因為感測器符合線性特徵。」

所以動態範圍似乎和感光的EV值範圍也有關？請問有大大知道兩者的差異嗎，EV值和dB值可以換算嗎？小弟不是學理工的，所以要請專家解惑。

pankang

pankang
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15樓

2008-04-13 2:32

看了一下英文的wiki大百科，作者直接把動態範圍Dynamic Range在照相領域中等同於曝光值Exposure Range.

然後他又提到：「 For example a good quality LCD display has a dynamic range of around 1000, or 30 dB (commercially the dynamic range is often called the "contrast ratio" meaning the full on/full off contrast ratio).」大意是好的LCD對比是1000:1，相當於30dB。

所以，有大大能算出E3在ISO100的曝光寬容值相當於多少dB嗎？（假如wiki的作者沒有寫錯的話）。

pankang

pankang
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16樓

2008-04-13 3:07

又找了一些外國有關感光元件的資料，來自clarkvision.com，裡面也提到動態範圍（Dynamic Range）。

http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary/#dynamic_range

這個網站似乎有很多相關資訊，但小弟累了，明天有精神再慢慢看吧。

subsub

subsub
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樓主

2008-04-13 4:59

pankang wrote:
看了一下英文的wik...(恕刪)

哈哈,pankang兄越來越靠近了,知道我要問甚麼了~

Linear Dynamic Range

The E-300 sensor's Linear Dynamic Range (LDR or DR) differs just slightly from the E-1. Will this make a difference in image quality? Strictly taking the numbers and using a special formula to determine the dynamic range, you might be surprised.
Dynamic Range is expressed in Decibels, i.e., dB. We get the dB number by the following forumula:

Dynamic Range = 20 x Log(Nsat/Nnoise)
Now, you're probably wondering just what the hek is this. It's simple, really:

1) Nsat is maximum amount of electrons that the pixel can hold (i.e., it's "well limit").

2) Nnoise is the maximum number of electrons which exhibit noise in each pixel.

What we get is this:

Step 1: Dynamic Range = 20 x Log(25,500/16)

Step 2: Dynamic Range = 20 x Log(1593.75)

Step 3: Dynamic Range = 20 x 3.2024

Step 4: Dynamic Range = 64.048

Step 5: Dynamic Range = 64.05dB

The E-1's Dynamic Range can be figured by just plugging in it's respective numbers. I think Kodak misplaced one of their numbers as we don't get 64.4, we get 64.05. However, if we do the E-1 figures, we get the same dB as they do (actually, 67.43dB).

Once again, the E-300 sensor is no slouch on the numbers and is just as good--at least on paper--as the E-1's sensor.

摘錄from http://www.digitaldingus.com/articles/oct/kaf8300ce.php

anoter site

Dynamic Range
The dynamic range of a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) image sensor is typically specified as the maximum achievable signal divided by the camera noise, where the signal strength is determined by the full-well capacity, and noise is the sum of dark and read noises. As the dynamic range of a device is increased, the ability to quantitatively measure the dimmest intensities in an image (intrascene performance) is improved. The interscene dynamic range represents the spectrum of intensities that can be accommodated when detector gain, integration time, lens aperture, and other variables are adjusted for differing fields of view.

Photodiode size determines, in part, the size of the depletion wells--larger diodes having greater full-well capacity compared to camera noise. Typical diode sizes in modern CCDs utilized in photomicrography range from 4.5 to 24 microns with corresponding well capacities of 20,000 to 600,000 electrons. Read noise is a combination of all noise generated during readout of the device. This includes noise from input clocking and fixed pattern, along with reset transistor noise and amplifier output noise. Read noise is usually specified in the performance data sheets that accompany a CCD sensor, with typical values ranging from 10-20 electrons/pixel in high quality chips operated at room temperature, and dropping to 2-5 electrons/pixel in Peltier-cooled CCDs for scientific imaging applications. The dynamic range is expressed in decibel units according to the following equation:

Dynamic Range = 20 x Log(Nsat/Nnoise)
where N(sat) is the linear full well capacity stated as the number of electrons and N(noise) is the total value of the read and dark noise, also expressed as the number of electrons. In a high-performance cooled CCD camera, the well capacity is proportional to the size of the individual photodiode, such that the maximum number of electrons stored is about 1000 times the cross sectional area of each photodiode. Thus, a CCD with 6.7 x 6.7 micron photodiodes should have a maximum charge storage capacity (a full-well capacity) of about 44,900 electrons (or holes). At a typical readout rate of 1 MHz, the read noise for this CCD is about 10 electrons/pixel, which yields a dynamic range of 44,900/10 or 4,490. In order to utilize the full range of grayscale levels available with this dynamic range, the camera should have a 12-bit analog-to-digital (A/D) converter capable of resolving 4096 gray levels. Controlling the size of the read and dark noise is a critical factor in maintaining a high dynamic range in these devices.

Higher performance cooled CCD sensors designed with low noise output amplifiers and suitable for use in slow-scan imaging of photomicrographs often have lower read noise and an extended dynamic range. As an example, the Marconi Applied Technologies CCD39-01 sensor is a back-illuminated, frame-transfer CCD having a square pixel size of 24 microns with a split output register allowing the utilization of quad output amplifiers. The full well capacity of this device can reach a level 300,000 electrons. Coupled with a readout noise root-mean-square (rms) level of three electrons at 20 kilohertz (when cooled), the CCD39-01 is capable of yielding a dynamic range of approximately 100,000:1. To fully utilize the potential of this CCD, a 17-bit A/D converter having 131,072 grayscale levels should be employed (although a 16-bit A/D converter having 65,536 grayscale levels would also suffice).

摘錄from http://www.olympusmicro.com/primer/digitalimaging/concepts/dynamicrange.html

我不是想知道E-3 在鏡頭下加減EV 的寬容度,
因為這個寬容度是透過olympus 鏡頭的表現,
而且廠商可以將整體偏移高光區或低光區,
這裡有圖表,
http://www.dpreview.com/reviews/olympuse3/page21.asp
廠商利用有限的動態去造就他們產品的特性,例如高光有細節(低光區就差),或低光還有細節(高光區就差),
因為可以用的動態就那些,它不會多出來,
再加上一些廣告圖,
有些user 就會誤以為"例"這台相機暗部表現的太好了,細節比別家(台)相機豐富多了..可是其它部份呢?
加上現今電動對焦鏡頭不能互換(卡口不同,接點不同),
這樣就會造就很多迷區及"迷"家(迷=O or C or N or P or S or F),讓大家爭得面紅耳赤~

我只是想知道E-3 那顆CMOS 到底有多強?是否有進步?這樣接手動鏡就較有利,

公式數值都有,我就是算不出來E-3 的(數學太差了)..

pankang

pankang
個人積分：42分
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42分

18樓

2008-04-13 12:52

subsub兄，今天凌晨又花了點時間，看了一些clarkvision.com的文章，逐漸拼湊出動態範圍、CCD（CMOS）的初步概念。這些網站引經據典，還附加其他網站的佐證，就學術觀點來說，它們的可信度是頗高的。

我先從CCD成相的文章看起（唉，我不是念理工的，K起來有點累）。簡單說，CCD（CMOS）的傳感器就像一個朝上的桶子，當它接收到一定的光線(photon，光子？)之後，就由數位類比轉換器開始處理訊號。因此傳感器開口越大，越能接收足夠的光線訊號，否則就會導致溢出（開口越小，一下子就滿了，再也裝不下訊號）。
(http://www.clarkvision.com/imagedetail/does.pixel.size.matter/index.html)

When pixels become very small, they hold so few electrons that dynamic range suffers, and this causes the turn down in AIQ at pixel sizes below 2 microns pixel pitch.
(畫素所佔的微米越小，它能容納的electron是如此之少，以致於減損了動態範圍，當畫素所佔的微米小於2的時候，會導致AIQ-Apparent Image Quality--大幅滑落)。

但傳感器的多寡，又牽涉到解析度。所以，在感光元件面積不變的情況下，如果能塞進越多傳感器，又維持合理的開口率，則達到雙贏的程度。否則，有一方勢必要被犧牲。我在photosharp看到過一個數據，好像每個pixel在6.8µmX6.8µm左右是最佳狀態。

由於牽扯的東西很多，所以慢慢看再消化，希望能釐清一點頭緒。不過，看到現在，似乎感光元件越大越有利。

issac2432

issac2432
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19樓

2008-04-15 13:16

我好像看到了學者，不過這種精神是好的，小弟我才疏學淺不知道怎麼才能窺門而入，不過樓上那篇動態範圍的文章我先前有看過，Leica M8也是67db.(資料來源好像來自對岸一個leica fan的網站中的某一篇)

Tommy Li

Tommy Li
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26分

20樓

2008-04-15 16:40

subsub wrote:
例如高光有細節(低光區就差),或低光還有細節(高光區就差),...(恕刪)

那麼，就人眼可分辨的動態範圍是很大的，LCD螢幕呢，CRT螢幕呢，有很多材質和設計的螢幕也大不相同。
照片最後還是要給人看的，顯示器的等級高低也有差別吧，加上如果有用到軟體的功能，也會影響輸出的結果。
我用LightRoom，Phtoshop，和Olympus Studio開啟同一張RAW檔就會得到三種不同明暗程度的照片。
要有標準的實驗室才能有公信力的測試出來吧~

http://www.flickr.com/photos/tommyli/