LAB彩色空間修圖法 (Lab Color Mode Adjustment)

最近在整理一些我過去幾年旅遊的影像包括北美和挪威北極等地區,主要整理一些風景的影像,將這些影像以一種更細緻的風貌呈現,過去在Lightroom的後製修飾其實已有很多功能可運用,使影像呈現更多元更藝術化的內容,來彌補拍攝時相機記錄的不足(包括曝光、色彩、白平衡等),Adobe Lightroom 是 Adobe公司發展的軟體提供職業攝影師以簡潔、快速的程式來達到處理大量影像的目的,最新版本更提供不同的筆刷局部修飾功能,使攝影師發揮創意修飾出更吸引人的影像,Adobe Lightroom是對整張影像的修飾有其速成的效果,但影像內個別”畫素”(Pixel)的顏色深淺和光線強弱、對比等等只能做一種總和式的調整,其中如色彩的調整無可避免的會影響亮暗對比,相同的如光線亮暗的調整也會影響色彩的飽和等,因此在整理過去影像的過程中,發現有些影像畫面應能更進一步展現其拍攝當時視覺上的實際色彩和明暗狀況,此時就須思考對影像中每個畫素(Pixel)的修飾,因此本篇的內容將說明以Adobe Photoshop 的Lab色彩模式即”色彩及明暗分離“的方法來修飾,展現出更精緻美麗的影像內容,其中的技巧包括Lab色域、色彩混和合器、圖層混合器及亮度/色彩圖層混和器等。

Recently I worked on some images that I took  some years ago during my travels, they are mainly the landscape images, to give those photos more delicate appearance, although the post processing in Lightroom make them already turning out to be in a good form which compensates the deficit from the camera capture (such as exposure、colors and white balance etc.),  Lightroom is an image fixing software of Adobe which can be easily managing a great amount of images in a short time, including category and development of the images adapted by many professional photographers, the current edition Lightroom CC providing some advanced function like radial graduating and local adjusting brushes, that photographer can be more creative in the post processing work flow. For already proper exposure images it will be quick and easy to adjust and fix, becoming more effectively in handling great amount of images, but for the tonal value and color contrast between pixels, the adjustment in the Lightroom can run into an interfere between tonal value and color contrast, for example when adjusting tonal value might increase or decrease the color contrast, on the contrary, when adjusting color contrast will also interfere the tonal value become darker or lighter, for a better enhancing those images which can be more reflecting the true tonal value and color contrast on the scene, we need to improve them by pixels in Photoshop, now I would like to explain in this blog about how to use Photoshop “Lab” trick to separate the tonal value and color contrast when enhancing, it includes” Lab color mode”、”channel mixer”、”layer blending modes” and” layer style blending option”etc..

以下簡單的敘述一下什麼是Lab色彩模式,它是Adobe公司的影像修飾軟體Photoshop特有的色彩模式中的一種,可以在Photoshop的選項中點選”影像”再點”模式”然後在下拉的目錄中找到”Lab Color”,那麼Lab代表的內涵是什麼,其中”L”代表亮暗對比,”a”代表色彩的洋紅和綠,”b”代表黃和藍,Lab運用在影像修飾的色偏校正或加強影像的色彩和明暗有很好的效果,因為它可在修飾時將影像的”色彩”及”明暗”分離操作,使影像不會產生過度的色彩及明暗對比,Lab色彩模式是類似人類視覺的色彩模式並有很廣的色彩區域,運用專業的軟體如Photoshop或Lightroom可將一些人類視覺看不到的顏色模擬到人類眼睛可看的色彩。

Now describing a little bit on” Lab color” mode, it is a unique color mode in the Adobe Photoshop, you can go to “Image” and “Mode” and choose “Lab color” in the collapsed panel, then what is L、a、b ? The “L” representing the “luminosity” of the image, the “a” representing  the color of “green” and “magenta”, the “b” representing the color of “blue” and “yellow”, Lab color mode offers a good effect in dealing with color casting or enhancing in the “tonal value” and “color contrast”, by separating “L” of luminosity  from “a” and “b” colors, the image will obtain its real tonal value and color and become more nature which closing to the human visual, furthermore, it can also mimic some colors which beyond human visual to be visible.

以下以實例來說明Lab色彩模式在影像修飾的操作方法:

以下兩張影像第一張是修飾前在Lightroom(也可在Photoshop的 ACR)裡做一些基本的修飾包括:白平衡、相機校正、曝光調整、鏡頭校正等,至於色彩飽和、明暗增強、影像銳利、極局部修飾等深入調整則在後續的Photoshop裡進行。

slide-2x

第二張影像是經過Lab色彩模式修飾後,呈現的色彩鮮豔及明暗鮮明影像是接近人眼視覺的自然影像。

slide-1x

Now, I pick 2 images to explain the “before” and “after” in adapting the Lab color mode:

In the following 2 images, the “before”one has done only some basic fixing or enhancing in the Lightroom( or in Photoshop ACR) including “white balance”、”camera calibration”、”lens calibration”、”exposure” etc., and then the images opened in the Photoshop for the “tonal value” and “color contrast” enhancement、”export sharpening” and some “local adjustment” etc.. the second one is after the “Lab” enhancement in Photoshop, which turned out to be an image of more dynamic tonal value and more saturated colors that is more closing to the human visual i.e. more nature.

slide-2xe

slide-1xe

步驟如下:

  1. 在Lightroom或Photoshop ACR(Adobe Camera Raw)裡載入影像後進行以下的”簡單”修飾:
    1. 設定白平衡:
      step1-1
    2. 相機校正(載入相機的色彩描述檔*)):step1-2
    3. 曝光調整:step1-4
    4. 鏡頭校正(鏡頭色差修正):step1-3
  2. 開啟檔案至Photoshop:
    1. 在”Photoshop“將檔案打開方法是點選ACR畫面下方的”開啟檔案”。
    2. 在”Lightroom”是點選 “相片” 在下拉方塊裡選 “在Photoshop開啟為smart 物件”**)step2-1
  3. 建議在Photoshop裡建立一個工作畫面以利後續的操作
  4. 這個工作畫面應包括3個控制板分別為 “資訊(INFO)” ,”調整(ADJUSTMENT)” 及 “圖層(LAYER)”
    step4-1
  5. 白平衡調整(建議執行):
    1. 在已打開檔案的”圖層”上增加一 “Threshold” 調整圖層,將下方的調整拉桿向右到底後陸續返回,以 “色彩取樣工具” 點擊最先出現的白點來設定影像的”亮”點,再以同法將調整拉桿向左到底後返回,設定影像的”暗”點(最先出現的黑點),完成後將 “Threshold” 調整圖層移除。
      step5-1
      step5-1_2step5-1-1-1
    2. 調整色彩:在調整控制板內點選 ”曲線控制”,在坐標圖方塊內點擊”RGB”下拉方塊,分別調整 “R”、”G”、”B” 坐標圖,並同時檢視 “資訊控制板” 內 “亮” 點和 “暗” 點的RGB值,直到 “亮” 點達 “245” 及 “暗” 點達 “15”。step5-2step5-2_1step5-2_2
    3. 將圖層扁平化成一新背景圖層。step5-3
  6. 色板混和器(Channel Mixer):
    1. 點選 “色板控制” (Channel),分別檢視 “R”、”G”、”B” 色板的明暗對比來決定要選用的色板。step6-1
    2. 在 “調整控制板” 內點選 “色板混和器控制”,在內建的下拉方塊內選擇一個或多個需要的 “色板混合器圖層”,雙擊圖層空白處在跳出的對話方塊內的”Knockout”下拉方塊裡選”深入”(Deep),使圖層與背景圖層連結。step6-2step6-2_1step6-2_2step6-6-2-1
    3. 在選取的 “色板混合器” 圖層裡將 “圖層混和模式” 改為 “光度” (Luminosity)模式,畫面還原為色彩。step6-4
    4. 如有需要利用 “遮蔽圖板” 在上述色板混合器作局部調整或增減圖層的 “透明度”。step6-4_1
    5. 點選畫面上方的 “影像” 選擇 “複製”,將上述一個或多個色板混合器圖層複製成一新檔案,並在跳出的對話方塊勾選 “圖層組合”。step6-5step6-5_1
    6. 新檔案 “影像” 內的 “模式” 改為 “Lab Color”。step6-6
  7. Lab色彩模式修飾:
    1. 在新建立的Lab檔案進行影像色彩增艷,在 “調整控制板” 內點選 ”曲線控制” 增加一曲線圖層,將 “圖層混和模式” 改為 “覆蓋”(Overlay),以滑鼠在此圖層的空白處雙擊,在跳出的對話方塊內的 “進階混和模式” 裡取消勾選 “L” 明暗色板,後按 “確定”。step7step7-1_2step7-1_4step7-1_3
    2. 在曲線圖層的下拉方塊中點選 “b” 色板(因此影像內有較多的”藍/黃”色彩),移動座標圖下方拉桿增加明暗對比至最大值(但不可超越原圖的曲線)。step7-2_1step7-2_2
  8. RGB色彩模式與Lab色彩模式融合:
    1. 將上述經 “曲線”調整過的Lab檔加入原來的RGB檔案,做法如下: 首先在原RGB檔案的圖層內加入一新圖層,點選畫面上方的 “影像” 然後選 “加入影像”,在跳出的對話方塊裡的 “來源” 下拉方塊選擇Lab檔、在 “圖層” 下拉方塊選 “融合”、 在 “色板” 下拉方塊選 “b” 後按 “確定”。step8-1step8-1_1step8-1_2step8-1_3step8-1_4
    2. 在RGB檔案,在加入的Lab檔案 ” b” 圖層的 “混合模式” 下拉方塊裡點選 “覆蓋”(Overly),然後雙擊此圖層的空白處,在跳出的對話方塊裡調整 “Bland If” 裡的 “上方圖層” 裡的 “亮部”拉桿向中間移至中間值 “128” ,來防止因 “覆蓋 “模式造成影像的亮部過強。step8-2_2step8-2_4step8-2_3
    3. 回到Lab檔雙擊 “曲線圖層”, 在跳出的對話方塊裡點選 “Bland If ” 下拉方塊裡的 “藍色” 色板,將 “上方圖層” 的 “藍色” 拉桿向中間移至中間值 “128”,以去除影像中過藍的色彩。step8-3_1step8-3_2
    4. 此時如造成影像中 “黃色” 部分過艷時,可先點選 “曲線圖層” 的 “白色遮蔽圖板”,在工具欄選取筆刷並將前景方塊設定 為 “” (遮蔽功能),在”黃色”過豔處塗抹,如須要將已塗抹處再部分回復,可選畫面上方 “影像” 再選擇 “調整” 再選 “Level”,在跳出對話方塊裡的 “Output Level”裡調整適當的輸出。
      step8-4_1step8-4_3step8-4_4step8-4_5
  9. Lab檔,按 “Comm.+A” 或windows的”Ctrl.+A”選取檔案,再按 “Comm.+C” 或windows的 “Ctrl.+C” 考備Lab檔。
  10. 選取RGB檔,按 “Comm.+V” 或windows的 “Ctrl.+V” 或 以另法點選 “編輯”, 再選 “貼圖” 將Lab檔加入RGB檔內,並在圖層的混合模式下拉方塊點選 “色彩”。step8-7_1step8-7_2
  11. 輸出銳利化:
    1. 選取RGB檔,按 “Shift+Comm.+E”或windows的 “Shift+Ctrl.+E” 增加一個濃縮圖層。step9-1_1
    2. 在畫面上方點選 “濾鏡”,再選 “銳利化”,再選 “非銳利化遮蔽”,在跳出的對話方塊理分別設定 “銳利值”、”範圍”、”門檻值” 然後按 “確定”。step9-2_1step9-2_2
    3. 在畫面上方點選 “編輯” 再選 “淡化非銳利化遮蔽” 在跳出對話方塊的 “模式” 下拉方塊選 “亮度” 後按確定,主要作用為減少因銳利化而造成色彩過度飽。step9-2_3step9-2_4step9-2_5
    4. 將上述銳利化圖層制作一考備圖層,分別將其命名為 “變暗”(Darken) 和 “變亮”(Lighten)兩個圖層,先勾消上方”變亮”(Lighten)圖層的”眼型圖”,後在下方 “變暗”(Darken)圖層的 “混合模式” 下拉方塊點選 “變暗”,後恢復勾選上方 “變亮”(Lighten)圖層的”眼型圖”,將其圖層的 “混合模式”下拉方塊點選 “變亮”, 如需要也可調整個別圖層的透明度來增減效果,以上作用為減少因銳利化形成不自然的亮/暗現像。
      step9-3_1
      step9-3_2
      step9-3_3
      step9-3_4
      step9-4_1
    5. 將圖層扁平化完成修飾工作,並按 “Comm.+S” 或windows的”Ctrl.+S”來儲存檔案。step8-5_1

*): 是以x-rite公司的Color Checker Passport色卡(24色)為基準在Lightroom或Photoshop軟體內建立一相機的色彩描述檔使色彩還原增豔

**): 採用此選項是避免在檔案轉到Photoshop後會在Lightroom自動建立一副檔案

The step by step are as the following: (Sorry for the language in images are Chinese)

        1. Open file in Lightroom or from Photoshop Bridge and proceeding some simple adjusting of:
          1. White balancestep1-1
          2.  Basic exposurestep1-4
          3. Camera calibration*) ( by X-rte color checker passport)step1-2
          4.  Lens chromatic abstraction            step1-3
        2. Open the file to Photoshop:
          1. In Photoshop ACR, click “open image” at the right lower end.
          2.   In Lightroom, click “image” and in the collapsed panel  choose “Open as a smart object file in Photoshop”**).step2-1
        3. For a time-saving processing, to set a layout of the screen with  the panel needed is important.
        4.  The working screen mentioned above should include the panel of “INFO”、”ADJUSTMENTS” and “LAYERS”.step4-1
        5. Adjusting the white balance (recommended):
          1. Select the “Threshold” adjustment in the adjustment panel, move the slide under all the way to the right and back until the first white appeared, get the “color sample tool” and click on it as the “white point“, and do the same way by moving to the left for setting the “ black point“, then remove the “Threshold” layer.
            step5-1step5-1_2step5-1-1-1
          2. Color balance: Choose “Curve” in the adjustment panel, in the Curve adjustment layer click ” RGB”, and adjust each of the “R”、”G”、”B” curve and examine the “INFO.” until each of RGB value of the “white point” reaches “245” and the “black point” reaches “15”.step5-2step5-2_1step5-2_2
          3. Flatten the layers.step5-3
        6. Channel Mixer:
          1. Click “Channels” in Layer panel to examine each channel of “R”、”G”、”B” to find out the best one of  the image tonal value.step6-1
          2. Then select the channels wanted from the “Channel Mixer” adjustment panel, double click the blank part of the channel layer, choose “Knockout” from the pop-up ” Layer Style” manual and select “Deep” for connecting to the background layer .step6-2step6-2_1step6-2_2step6-6-2-1
          3. Change the blending mode of the selected channels from “Normal” to “Luminosity” to get the color.step6-4
          4. Use layer mask if needed for local adjustment or adjusting opacity of the selected channels.step6-4_1
          5. Go to “Image” and select “Duplicate” to copy the selected channel layers and check the “duplicate the merged layers only” and click “Ok”.step6-5step6-5_1
          6. In the new file, go to “Image” then “Mode” selecting “Lab color”.step6-6
        7. Lab color mode adjustment:
          1. To enhance the color contrast in the Lab color mode file, in the adjustment panel choose “Curve” to get a curve layer and changing the blending mode to “Overlay” for more contrast, double click the blank part of the “Curve” layer, from the pop up panel of “Layer Style” , unchecking the “L” channel for separating the luminosity in the coming adjustment, then click “Ok”.step7step7-1_2step7-1_4step7-1_3
          2. In the “Curve” layer choose “b” channel (because there are more blue/yellow in this image), and increasing the color of “blue” and “yellow” by moving the slide from both ends inward until to the edge of the curve (do not go in the curve).step7-2_1step7-2_2
        8. The combination of the Lab and RGB color:
          1. In RGB color file, click “Create a New Layer” icon under the layer panel, then go to “Image” and choose “Apply Image”, in “Source” of the pop up panel selects the Lab color file, in “Layer” selects “Merged”, in “Channel” selects “b”, and then click “Ok”.step8-1step8-1_1step8-1_2step8-1_3step8-1_4
          2. Back to the Lab color file, in the “curve” layer, double click the blank part to get the layer style, in the “Blend If” section, choose “b” and move the blue end inward to neutral value of “128” for getting rid of the blue casting.step8-3_1step8-3_2
          3. If there is too strong yellow color after last step, then select the white mask in the “curve” layer and picking the brush tool and setting the foreground patch to black (masking), to brush the strong yellow color parts, if the brushed parts needed to be restored, then go to “Image” choose “Adjustment” and “Level”, move the “output” slider from the dark side inward until it shows properly.step8-4_1step8-4_3step8-4_4step8-4_5
          4. Flatten layers.step8-5_1
          5.  Now insert the flattening  Lab color file to RGB color file  , in Lab color file hold down “Comm.+A” of Mac or “Ctrl.+A” of windows to select file and “Comm.+C” of Mac or” Ctrl.+C” of windows to copy the file.
          6. In RGB color file, hold down “Comm.+V” of Mac or “Ctrl.+V” of windows to paste the Lab color file, or go to “Edit” and choose “Paste” to get the Lab color file on top of the existing layers, change the blending mode of the new layer to “Color“.step8-7_1step8-7_2
        9. Output sharpening:
          1. In RGB color file, hold down “Shift+Comm.+E” of Mac or “Shift+Ctrl.+E” of windows to get a condensed layer on top.step9-1_1
          2. Go to “Filter” choosing “Sharpen” and then “Unsharp Mask”, adjusting  the proper value of “amount”、”Radius” and ” Threshold”, and then click “Ok”.
            step9-2_1
            step9-2_2
          3. Go to “Edit” and click “Fade Unsharp Mask”, selecting “Luminosity” from the “Mode” of the pop-up panel and click “Ok”, for against the over  saturation of the color after sharpening.
            step9-2_3step9-2_4step9-2_5
          4. Under the layer panel, click  “Create a new layer” icon to get a copy of sharpened layer, named the one down as “Darken”, and the one up as “Lighten”, to adjust the “Darken” layer by unchecking the eye thumb nail of the “Lighten” layer, change the blending mode of the “Darken” layer to “Darken”, checking  again the eye thumb nail of the upper “Lighten” layer  and changing the blending mode of the “Lighten” layer to “Lighten”, for getting a proper sharpening in the bright and dark of the image.step9-3_1step9-3_2step9-3_3step9-3_4
          5. If needed, moving the opacity slider at the upper right hand corner of the layer panel to balance the effect.step9-4_1
          6.  Flatten  layers and hold down the “Comm.+S” of Mac or或的”Ctrl.+S” of windows to save the file.step10-1

*): Take an image of the color patch of the Color Checker Passport of x-rite co., and the plug in of the Color Checker Passport will create a camera calibration file.

***): Choose this function is free of a automatic copy file in Lightroom after exporting the file to Photoshop.