設定相機的色彩描述檔(Camera Color Calibration)

一張影像拍攝的成功與否最重要的觀察點是影像的亮暗分佈及細節而非色彩,也就是由最暗最亮部分的灰階是否平滑及呈現細節,然後由安裝在相機感光裝置上的彩色濾片依光現亮暗的程度轉換成彩色影像,因此一張漂亮的照片須從正確的曝光獲得,也就是能呈現愈多的由完整的灰階。

We see a pretty photo that amaze us is because of its tonal value i.e. it’s bright and dark map but not its colors, that is the displaying of the dark to the bright zones have a smooth steps and details, and the color which we see is coming out from the color filters in front of the camera sensor according to the tonal value captured by the camera. But a pretty color photo will not only come from a more zones of bright and dark tonal value during the camera capture but also the  color consistency .

但有了一張正確並完整灰階的曝光後是否就表示自然也是一張漂亮的彩色照片呢?其實未必,漂亮的色彩是要能接近人類視覺且不會因成像(相機、掃描器等)或顯示(顯示器、網路等)工具的差異而改變,因此現代數位攝影對成像顯示等工具的校正工作是不可或缺的,主要目的是要確保色彩一致不變。

This time I would like to talk about why the perfect capture of tonal value is not the only factor for an awesome color image, a pretty color photo should be consistent and mimic the human vision, and not affected by different capture devices (such as camera or scanner), and different displaying devices (like monitor or web etc.), so in the digital photography, we have to fix or calibrate the capture and the displaying equipments for a consistent color rendering.    

現在來說明一下Adobe公司的 “數位負片檔案編輯器” (DNG Profile Editor),它是一個使用在Adobe影像修飾軟體包括PhotoshopACR(Adobe Camera Raw)及Lightroom裡的應用檔案,主要功能是修改或調整影像的原始資料(Raw Data) 檔再轉換出一數據對照表使其成為一個色彩標準,再將此色彩標準與一24色標準色板相對照後產生一修正數據檔案,並將其儲存在PhotoshopACR(Adobe Camera Raw)或Lightroom裡形成該特定相機的色彩描述檔

Before we talk about the camera color calibration, I would like to mention the Adobe DNG Profile Editor, it is an application file which used in the Photoshop ACR and Lightroom, what the DNG profile Editor doing is transforming the raw data of the camera to a look up table as a color reference, and comparing it with a  24 standard color patches to introduce a data profile and save in the Photoshop ACR or Lightroom as the camera calibration file for that special camera.

以上的說明看似蠻複雜的,現在市面上有一包裹工具(X-Rite公司的Color Checker Passport)包括硬/軟體,可非常容易的自動完成相機色彩描述檔的整個設定,在以下的實例中須要提醒的是拍攝目標色板時,需要取得曝光正確的影像,使設定軟體時能獲得較準確的色彩參考值,至於設定不同色溫的光線可大致分為日光、陰天、陰影、鎢絲光等,以下說明設定的步驟:

It sounds complicated with the above explanation, but now we can choose a tool from company X-Rite who offers the product of “Color Checker Passport” package including software, it can be very easy to establish the camera calibration profile in Photoshop and Lightroom, the main point is we should shoot a proper exposed and relative sharp color patch image and resulting a more precise camera calibration profile, as to the variety color temperature of lighting are normally choosing daylightovercastingshade and tungsten etc., now explain it step by step as following:

color checker

目標色板 / Color Checker Passport (X-Rite)

  1. 目標色板拍攝
    1. 目標色板置於光線均勻的地點。
    2. 依採用的光線(日光、陰天、陰影、鎢絲光等)設定相機,包括光圈、快門及ISO值,須使目標色板的影像曝光適當、影像清楚。
  2. 軟體設定
    1. 在Photoshop
      1. 在Bridge或其他檔案夾裡將拍攝的目標色板開啟至Photoshop的影像原始資料處理器(ACR),選取畫面左下方的 “儲存影像” 按鈕將影像轉換成數位負片(DNG)檔,在跳出的畫面裡輸入 “儲存位置“、”檔名” 後按 “確定“。slide-4
      2. slide-5
      3. 打開電腦內的Color Checker Passport 應用軟體。
      4. 在畫面上方選取 “文件” 後,點選 “添加圖案“,或直接將檔案拖曳到畫面中間的檔案區。
      5. slide-7
      6. slide-6
      7. 在軟體處理後出現的目標色板影像畫面,點選下方的”創建配置文件“按鈕,在跳出的畫面輸入檔名後按 “儲存“。slide-8
      8. slide-9
    2. 在Lightroom
      1. 打開拍攝的目標色板檔並將其轉換成數位負片(DNG)檔案。slide-12
      2. 目標色板檔案的24色色板部分裁切,使軟體較容易辨識。slide-15
      3. 在畫面上方選 “檔案“,再點選 “使用預設集轉存” 再選 “Color Checker Passport”。slide-13-1
      4. 在跳出的對話方塊輸入要建立檔案的檔名後按 “確定“。slide-14-1
      5. 在畫面出現 “檔案已建立成功” 的訊息後,按 “” 完成建檔。slide-16
      6. 此時Lightroom需關閉再重新開啟。
  3. 色彩描述檔選用
    1. 在Photoshop
      1. 打開要後製的影像原始檔進入Photoshop ACR。
      2. 在畫面右欄上方點選 “相機校正“,在下拉方塊裡點選上述建立的色彩描述檔。
      3. 回到 “基本” 欄將白平衡點選 “拍攝時設定“。slide-10
      4. slide-10-1
    2. 在Lightroom
      1. 打開要後製的影像原始檔。
      2. 在右欄點選 “相機校正“,在下拉方塊裡點選上述建立的色彩描述檔。
      3.  回到 “基本” 欄將白平衡點選 “拍攝時設定“。slide-17
      4. slide-18
  4. To shoot a color patch image:
    1. Put the color patch card in an even lighting place.
    2. Set the camera in each different lighting (such as daylight、overcasting、shade and tungsten etc.), including aperture、shutter and ISO, the image should be clear and exposing properly.
  5. Operating the software:
    1. In Photoshop:
      1. Open the raw color patch file from Bridge or other location to Photoshop in the ACR (Adobe Camera Raw), click “Save Image” at the left end corner for saving the files to DNG format, key in the “Destination” and “File Name” and click “Ok”.slide-4
      2. slide-5
      3. Open the Color Checker Passport application file to establish a camera calibration file.
      4.  Select “File” and “Add an Image” to input the color patch DNG file to the application file or just dragging the color patch DNG file to the blanking part in the screen.slide-7
      5. slide-6
      6. When the color patch displaying on the screen, click the button “Create Profile” to establish the camera calibration file, and add the file name then click “Ok”.slide-8
      7. slide-9
  6. In Lightroom:
    1. Open the raw color patch file in Lightroom and save the files to DNG format.slide-12
    2. Crop the 24 color patch part of the file for easing the process.slide-15
    3. Select “File” and “Export with Preset” and the “ColorChecker Passport“.slide-13-1
    4. Key in the name of the file in the pop-up diagnose block and click “Saveslide-14-1
    5. After the message showed profile has successfully generated, then click “Ok“.slide-16
    6. Lightroom has to be reopened to adapt the profile.
  7. Adapting the camera calibration profile:
    1. In Photoshop:
      1. Open the image files in the Photoshop ACR.
      2. Click the “Camera Calibration” at the tool bar, select the profile generated.
      3. Click the “Basic“, in the “White Balance” select “As shot“.slide-10
      4. slide-10-1
    2. In Lightroom:
      1. Open the image files.
      2. Click the “Camera Calibration” in the right panel, and select the profile generated.
      3. Click the “Basic“, in the “White Balance” select “As shotslide-17
      4. slide-18