外國有用家發起要求 Sony 改善 A7 系有損式壓縮 raw file的問題

本帖最後由 singlag 於 2015-5-12 19:47 編輯

Enable uncompressed or lossless compression RAW files on the A7 cameras and future (F)E mount cameras.

https://www.change.org/p/kazuo-h ... e-f-e-mount-cameras

Due to the fact that lossy compression (which basically means that data is thrown away from the RAW file in order to keep the file size down) is applied to the RAW files in all of the A7 cameras (and possibly other Sony cameras too), artifacts start to show up. These artifacts are visible in certain parts of the image when lifting the exposure/shadows by a couple of stops, but sometimes even show up when hardly any image processing was done.

1) A quote from an article on the RawDigger website:

"All that is necessary for the artifacts to threaten the quality of the final image is a combination of high local contrast and a flat featureless background."

2) A quote from a forum post by Fred Miranda on the Fred Miranda forums:

"I was able to replicate a situation where the compression is visible. When shooting a high contrast subject where the shadows are very close to pure black. When trying to recover the shadows, artifacts become very apparent."

One might ask if this issue is caused by the lossy compression that is applied to the Sony RAW files. Let's compare an ISO100 Sony A7 II RAW file to an ISO100 Nikon D750 RAW file (which both use a very similar Sony EXMOR 24.3MP fullframe sensor). This can easily be done by downloading the RAW files from the "New studio scene comparison tool" on the DPReview website.

You can find a quick comparison I've made, right here:

Sony A7 II RAW vs Nikon D750 RAW

As you can see, the artifacts are not there in the Nikon D750 RAW file which is merely 6,5 MB bigger in file size (24 MB for the Sony A7 II RAW file vs 30,5 MB for the Nikon D750 RAW file). Because of this, it's (very) sad to see that Sony is crippling the performance of their sensors in the A7 cameras by applying lossy compression to the RAW files.

支持!

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回覆 2# harryytm


應該改成  D600 禁有 4 個 options
NEF (RAW): 12 or 14 bit, lossless compressed or compressed

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其實有冇諗過Nikon既14bit/12bit/cRAW/RAW甚至Canon既大RAW/細RAW可能係唔同廠既唔同特色...
咁不如搞過聯署,要求Sony/Canon加入埋對焦點連動測光,Canon要行FHD 60/50P...

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回復 4 #ahshing

你個建議都唔錯
講真, 係用家立場當然功能越多越齊就越好, 更加唔會把缺點當特式

良性競爭應該係列出缺點, 改善為比對手更好, 禁用家先會 buy, 有口碑

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好似發起咗幾個月. 都唔夠1,500人 簽名支持. 看來大部份sony用戶都無乜要求.

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本帖最後由 harryytm 於 2015-5-13 01:45 編輯

唔知道師兄對於"對焦點連動測光"的定義係咩,以我理解Canon的"權衡式測光"係同一樣野。

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S記搞下個 jpg engine 同 高ISO (software) 先啦
以上應該係所有日本廠最差果間,好心就炒晒班友

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對焦點連動重點測光... 好老實... 好似係件好事,事實上呢?
遇上個連測光要點測同點樣去用曝光補償都唔多識唔多熟
o既用家去用, 多數都會係出事多過無事~~~~~

對應返 Canon, 呢個功能都係最高級機先有, 原因就係買得
呢 D 機o既用家 "應該" 有足夠能力去擅用呢個功能o既好處,
同埋有足夠經驗係實拍過程中缺即時修正 ,亦即係擅用曝光
補償, 而一般用家就未必有呢個經驗同能力, 亦因此係其他機
型上都無呢個功能而簡化成中央一點重點測光...

而多區域測光方式同對焦點連動個方式係方便用家係用多點
AF 時部機可以更準確咁測光, 而且經過咁多年演進, 呢個方式
對一般情況下已經夠用, 當然你硬係要大背光影人像又要部機
真係測光測得準係好難... 呢個時候點都要自己動手加曝光補償
就係了... 唔係多數都係唔多掂矣~~~~
(多區測光由 Nikon FA 至 OM o既 ESP 後來 EOS 個權衡式測
光都係講緊 1983 至 1987 年年代o既事, 都差唔多三十年o黎...
無任何改進似乎唔太可能o卦?)

大慨係咁...

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本帖最後由 singlag 於 2015-5-13 02:44 編輯

回覆 7# harryytm

佢意思應該係 "點測光 + 對焦點連動"
即係當你用點測光時, 唔會只用中間果點做測光, 而係自動根據你的對焦點位置去做點測光, 禁就唔洗先點測光 + AEL 再構圖禁煩 (例如想對面部做點測光時, 直接對焦就 ok)

呢點係 Canon 機上係沒的, 但 Canon 個測光系統會自動視對焦點的光暗去做補償, 即係構圖不變時, 更改對焦點, 個自動曝光值會有所不同, 睇你對焦位係光定暗了 (Eos-M 係禁);  而 Sony / Fuji 個測光系統係沒呢個補償, 因此 2 個系統係操作上會有少少分別

禁用 Canon 可能係就禁"權衡式測光", 再由機身自己視對焦點去補償自動曝光值 (如沒人手更改 EC 的話, 一樣顯示為 +-0EV), 基本上都足夠使用了, 因為機身都自動做左曝光補償。 真係有需要先再用點測光, 不過就要先中間點測光再 AEL, 後構圖對焦
而用 Sony / Fuji 可能就係自己睇情況決定用咩測光模式, 但個"點測光"會方便用家, 機身識自動同對焦點連動, 可以直接構圖對焦, 唔洗 AEL

另外 Sony 有個功能可以 set AEL 時自動用點測光, 即係平時 set 左用全畫面測光, 但當你按 AEL 時, 佢會即時轉用點測光再 AEL, 之後回復番做全畫面測光

間間廠都有不同好用的功能, 但又欠缺左人地的功能。作為消費者 + 用家, 係知道左自己所用的系統欠缺左咩功能之後, 應該反映出來比間廠知, 禁至少下代機先會有實際進步, 正如 Nex 系的操作不便而出現的 Tri-navi,A7 的光暈事件而修正的 A7-Mk2

呢點做得最好係 FujiFilm, 不停出新 firmware 去修正同加強舊有機身, 例如自定安全快門值, 呢個係 A7 系所欠缺而又應該有的; M mode 下用 Auto ISO, 本身 C/F/S 當中只係 Sony 支援手動曝光補償, 但現在 Fujifilm 的 X-T1 都會係  Ver4.0 當中加入呢個功能

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