{"slug":"exposure-bracketing-blending","title":"再大光比也不用怕 - 包围曝光与曝光合成技术详解","author":"Thomas看看世界","date":"2017-05-07","wechat":"https://mp.weixin.qq.com/s?__biz=MzI4NDA5MzE5NQ==&mid=2247485486&idx=1&sn=0f7ecdededd9b92e54f0bf2399fe5256&chksm=eb81f64adcf67f5cd511787e3640f231e30be4ec6c2b867d00521dd313eb797a19284ea61ad0&scene=21#wechat_redirect","blocks":[{"t":"p","x":"在遇到逆光等大光比情况时，画面中最亮和最暗的地方相差太大，导致相机无法记录，要么过曝，要么欠曝。","b":false,"xe":"In backlit and other high-contrast situations, the brightest and darkest parts of a scene differ so much that the camera can't record both — you get either blown highlights or crushed shadows."},{"t":"p","x":"而前期的包围曝光技术，以及后期的曝光合成技术，则可以完美的解决大光比下曝光的难题。","b":false,"xe":"Exposure bracketing on location, and exposure blending in post, perfectly solve the high-dynamic-range problem."},{"t":"h","x":"1","xe":"1"},{"t":"h","x":"前期包围曝光技术","xe":"On-Location Exposure Bracketing"},{"t":"p","x":"包围曝光，指的是拍摄多张等差曝光量的相片，如欠曝一档、正常、过曝一档。这个功能以前主要用于光线复杂，相机不易正确测光的场合。先连续拍摄多个曝光量的照片，总有一张是刚好曝光正常的，这样保留正常的这张，删掉其他曝光不对的，我们就完成了准确曝光。","b":false,"xe":"Exposure bracketing means shooting multiple frames at evenly spaced exposure values — e.g. one stop under, normal, one stop over. It was originally used in tricky lighting where the camera's metering might fail: shoot several exposures and keep the correct one."},{"t":"p","x":"而在后期技术突飞猛进的今天，包围曝光技术，已经主要用来克服相机宽容度的局限。（如果对宽容度、光比等名词不熟悉，可以阅读我以前的文章《数码时代如何正确曝光》）。","b":false,"xe":"Today, with post-processing advancing rapidly, bracketing mainly serves to overcome the camera's dynamic-range limit. (If terms like dynamic range and contrast ratio are unfamiliar, read my earlier article 'How to Expose Correctly in the Digital Age'.)"},{"t":"p","x":"比如环境中的光比如果有20档，而我们的相机宽容度只有12档。无论我们怎样调整曝光参数，单张照片都必然会过曝或者欠曝。而包围曝光技术可以解决这样的大光比问题。","b":false,"xe":"For example, if the scene spans 20 stops but your camera covers only 12, no exposure setting can avoid clipping somewhere in a single frame. Bracketing solves exactly this problem."},{"t":"p","x":"我们可以设置相机到AEB自动包围曝光模式，曝光张数为5，曝光补偿量为2EV（2档）。这样连拍5张照片，我们就可以分别记录下0-12，2-14，4-16，6-18，8-20的全部环境亮度信息。","b":false,"xe":"Set the camera to AEB (auto exposure bracketing) with 5 frames at 2 EV steps. Five consecutive frames then record the full scene brightness in windows of 0-12, 2-14, 4-16, 6-18 and 8-20 stops."},{"t":"p","x":"后期再用HDR或者亮度蒙版等曝光合成方式，把这5张照片合成到一起，我们就获得了一张超大光比的照片。比如下面这个例子。","b":false,"xe":"In post, blend the five frames with HDR or luminosity masks, and you get one super-high-contrast image. Like the example below."},{"t":"p","x":"包围曝光照片1：ISO200，f16，曝光3秒，整体欠曝但保留高光细节","b":false,"xe":"Bracket frame 1: ISO 200, f/16, 3 seconds — overall underexposed but preserving highlight detail"},{"t":"img","f":"img-02","w":1000,"h":664},{"t":"p","x":"包围曝光照片2：ISO200，f16，曝光13秒 （增加2档曝光），整体过曝但记录下暗部细节","b":false,"xe":"Bracket frame 2: ISO 200, f/16, 13 seconds (+2 EV) — overall overexposed but recording shadow detail"},{"t":"img","f":"img-03","w":1000,"h":664},{"t":"p","x":"后期用Adobe Camera Raw（ACR）合成并处理后的结果：","b":false,"xe":"The result after blending and processing in Adobe Camera Raw (ACR):"},{"t":"img","f":"img-04","w":1000,"h":704},{"t":"p","x":"前期包围曝光的时候，我们可以手动调整每张照片的曝光补偿，也可以使用相机自带的AEB自动包围曝光模式。","b":false,"xe":"When bracketing on location, you can adjust exposure compensation manually for each frame, or use the camera's built-in AEB mode."},{"t":"p","x":"在AEB自动包围曝光模式下，我们可以设置拍摄张数，曝光补偿量，和曝光方向，在我们按下快门的时候，相机就会自动调整曝光参数，完成包围曝光。（如果驱动模式设为单拍，则必须按多次快门按钮。当相机设为高速连续拍摄或低速连续拍摄时，持续完全按下快门按钮，相机会连续拍摄多张包围曝光的照片。）","b":false,"xe":"In AEB mode you set the number of frames, the EV step, and the direction; when you press the shutter, the camera changes the exposure settings automatically. (With single-shot drive, you must press the shutter multiple times. In high- or low-speed continuous drive, holding the shutter down fires the whole bracketed sequence.)"},{"t":"p","x":"AEB自动包围曝光模式的设置方法，各个相机型号有所不同。有的需要在拍摄菜单中设置，有的相机则有专门的BKT（bracketing，包围连拍）按键。","b":false,"xe":"How to configure AEB varies by camera model: some require the shooting menu, others have a dedicated BKT (bracketing) button."},{"t":"p","x":"BKT按键可以配合主指令转盘和副指令转盘，调整包围曝光的张数和曝光补偿量。具体调整方式，请仔细阅读你的相机说明书，关于AEB/BKT/包围曝光的相关章节。","b":false,"xe":"The BKT button works with the main and sub command dials to set the frame count and EV step. Consult your camera manual's AEB/BKT/bracketing chapter for specifics."},{"t":"p","x":"包围曝光一般有3个参数可以选择。","b":false,"xe":"Bracketing generally offers three parameters."},{"t":"p","x":"第一个参数是曝光补偿量，也就是每张照片的曝光量差别。一般有0.3，0.7，1，2，3等选项。如果你选择1，则表示每张照片曝光相差1档（1EV）。在光圈优先模式下，就表示两张照片之间，快门时间是2倍的关系。","b":false,"xe":"The first is the EV step — the exposure difference between frames, commonly 0.3, 0.7, 1, 2 or 3. Choosing 1 means each frame differs by one stop (1 EV); in aperture-priority mode, that means the shutter speed doubles between frames."},{"t":"p","x":"曝光补偿量，我最常用的设置是2EV（2档）。因为小于1的曝光差别，后期ACR里拉一下曝光度就可以轻松找回，没有必要。而且曝光补偿量设置过小，会使得拍摄张数变多。不仅增加后期难度，而且拍摄过程稍有晃动（或者有云等运动物体），还会造成合成后锐度下降、出现重影的现象。","b":false,"xe":"My most-used setting is 2 EV. Differences under 1 EV are unnecessary — ACR can recover that with one exposure slider — and too small a step means more frames to shoot, which complicates post and, with any camera shake (or moving objects like clouds), reduces sharpness and creates ghosting after blending."},{"t":"p","x":"而3档、4档的曝光差别太大，后期合成后有可能出现细节丢失、噪点增多的情况。只有2档（2EV）的设置，不多不少刚刚好。","b":false,"xe":"Steps of 3-4 EV are too wide, risking detail loss and extra noise after blending. Two stops (2 EV) is just right."},{"t":"p","x":"第二个参数是包围曝光张数，常见的有2张、3张、5张、7张等等。张数的设定，我一般使用先试验，后调整的策略。保证连拍的照片里，最暗的那张，直方图右侧不被切断（也就是记录下了环境中最亮的区域）。","b":false,"xe":"The second parameter is the frame count — commonly 2, 3, 5 or 7. My strategy is test first, then adjust: make sure that in the darkest frame, the histogram's right edge isn't clipped (meaning the scene's brightest area is recorded)."},{"t":"img","f":"img-05","w":640,"h":418},{"t":"h","x":"最亮的那张，直方图左侧不被切断（也就是记录下了环境中最暗的区域）。","xe":"And in the brightest frame, the histogram's left edge isn't clipped (meaning the scene's darkest area is recorded)."},{"t":"img","f":"img-06","w":640,"h":418},{"t":"p","x":"比如我先设置曝光补偿2EV，包围3张。然后检查最暗和最亮的两张照片的直方图，如果有边缘切断的现象，就需要增加包围的张数，比如增加到5张或者7张。","b":false,"xe":"For instance, I start with 2 EV × 3 frames, then check the histograms of the darkest and brightest frames. If either edge is clipped, I increase the count to 5 or 7."},{"t":"p","x":"还有第三个参数，就是包围曝光的方向。同样2EV，包围三张，如果设置成双向（-+），相机会拍摄-2EV（欠曝2档），0（正常曝光），+2EV（过曝两档）三张照片。如果设置成+单方向，相机就会拍摄0，+2EV，+4EV三张照片。如果设置成-方向，相机则会连拍0，-2EV，-4EV三张照片。","b":false,"xe":"The third parameter is direction. With the same 2 EV × 3 frames: bidirectional (−+) captures −2 EV, 0, +2 EV; positive-only captures 0, +2 EV, +4 EV; negative-only captures 0, −2 EV, −4 EV."},{"t":"p","x":"下面这张截图里相机肩屏的设置，3F表示包围张数为3张，2.0代表曝光补偿量为2EV。下面的方向显示中，从+到-都有，表示包围曝光时会双向包围。也就是相机会拍摄+2EV过曝2档，0EV正常曝光，-2EV欠曝2档，3张照片。","b":false,"xe":"In the screenshot of the camera's top LCD below, '3F' means 3 frames and '2.0' means a 2 EV step. The direction indicator spans + to −, meaning bidirectional bracketing: the camera shoots +2 EV over, 0 EV normal and −2 EV under — three frames."},{"t":"img","f":"img-07","w":1000,"h":760},{"t":"h","x":"2","xe":"2"},{"t":"h","x":"后期曝光合成技术","xe":"Exposure Blending in Post"},{"t":"p","x":"前期我们用包围曝光的方式，用多张照片记录下了环境中的全部亮度信息。后期的时候，我们则需要用曝光合成的相关技术，把多张照片合成到一起。","b":false,"xe":"On location we recorded the scene's full brightness range across multiple frames. In post, exposure-blending techniques merge them into one image."},{"t":"p","x":"后期曝光合成，主要分为手动合成和自动合成。手动合成技术，以画笔、蒙版组、亮度蒙版等为代表，托马斯会在以后的教程中进行介绍。而自动合成技术，则以ACR、Photoshop、Photomatix、Nik HDR等软件中的自动HDR合成技术为代表。","b":false,"xe":"Blending divides into manual and automatic methods. Manual methods — brushes, mask groups, luminosity masks — will be covered in future tutorials. Automatic methods are represented by the auto-HDR features in ACR, Photoshop, Photomatix, Nik HDR and similar software."},{"t":"p","x":"这里托马斯将介绍ACR（以及类似的Lightroom）中的HDR合成方法。ACR中的HDR合成非常简单，而且生成的是DNG数字底片格式文件（类似raw文件），蕴含了大量信息，给后期的进一步调整提供了无限的可能。","b":false,"xe":"Here Thomas introduces HDR merging in ACR (and the similar Lightroom). It's very simple, and it outputs a DNG digital negative (like a raw file) packed with information — offering endless room for further adjustment."},{"t":"p","x":"下面的例子，我会用这3张曝光差别为2EV的包围连拍照片，进行ACR的HDR合成。","b":false,"xe":"In the example below, I'll merge three bracketed frames spaced 2 EV apart using ACR's HDR."},{"t":"p","x":"包围照片1，0EV，窗户外完全过曝，取得画面暗部细节：","b":false,"xe":"Bracket frame 1, 0 EV: the window view is completely blown, but the interior shadow detail is captured"},{"t":"img","f":"img-08","w":664,"h":1000},{"t":"p","x":"包围照片2，-2EV，拍摄画面较亮部分细节。","b":false,"xe":"Bracket frame 2, −2 EV: captures detail in the brighter areas."},{"t":"img","f":"img-09","w":664,"h":1000},{"t":"p","x":"包围照片3，-4EV，记录环境最亮部分细节。","b":false,"xe":"Bracket frame 3, −4 EV: records detail in the scene's brightest parts."},{"t":"img","f":"img-10","w":664,"h":1000},{"t":"p","x":"首先要在ACR中一起打开这3张照片，如果在文件夹中，可以选择这3张照片，然后鼠标右键，选择“打开方式-Adobe Photoshop”。","b":false,"xe":"First, open all three photos together in ACR. From a folder, select the three, right-click, and choose 'Open with — Adobe Photoshop'."},{"t":"img","f":"img-11","w":1000,"h":861},{"t":"p","x":"如果是使用Bridge浏览照片，也是选上3张照片，右键选择“在Camera Raw中打开”。","b":false,"xe":"If you browse with Bridge, likewise select the three photos, right-click and choose 'Open in Camera Raw'."},{"t":"img","f":"img-12","w":1000,"h":672},{"t":"p","x":"在ACR中打开照片之后，在软件左侧可以看到3张略缩图，鼠标右键点击任一一张略缩图，在菜单中选择“全选”。","b":false,"xe":"Once open in ACR, you'll see three thumbnails on the left. Right-click any thumbnail and choose 'Select All'."},{"t":"img","f":"img-13","w":647,"h":1000},{"t":"p","x":"全选之后，再点击鼠标右键，此时打开的菜单中，出现了“合并到HDR”的选项，选择此选项。","b":false,"xe":"With all selected, right-click again — the menu now shows 'Merge to HDR'. Choose it."},{"t":"img","f":"img-14","w":630,"h":1000},{"t":"p","x":"一会儿之后，我们就进入了HDR合成面板。面板上主要有3个设置项。","b":false,"xe":"A moment later you enter the HDR merge panel, which has three main settings."},{"t":"p","x":"第一个是“对齐图像”，一般我们都勾上“对齐图像”，因为即便用三脚架拍摄，按动快门时仍然会有微小位移。如果不对齐多张照片的话，合成后锐度会大大下降。","b":false,"xe":"The first is 'Align Images' — usually keep it checked, because even on a tripod, pressing the shutter causes tiny shifts. Without alignment, the merged result loses a lot of sharpness."},{"t":"p","x":"第二个是“自动色调”，这个选项我们也一般都勾上。勾上“自动色调”之后，ACR会自动调整照片的曝光度、高光、阴影、白色、黑色这几个滑块，让照片得到一个推荐的细节和对比程度。这些调整是非破坏性的，我们之后可以在基本面板中重新设置。","b":false,"xe":"The second is 'Auto Tone', also usually checked. With it on, ACR automatically sets the Exposure, Highlights, Shadows, Whites and Blacks sliders for a recommended level of detail and contrast. These adjustments are non-destructive and can be reset later in the Basic panel."},{"t":"img","f":"img-15","w":1000,"h":776},{"t":"p","x":"最下面有一个“消除重影”的下拉菜单，有“关、低、中、高”这4个选项。一般我都选择“关”，只有画面中有移动物体，而且合成之后出现重影时，才根据重影的程度，选择“低、中、高”的选项。（如下图中，两张包围曝光照片拍摄时，轮船有移动，合成后出现半透明的重影）","b":false,"xe":"At the bottom is the 'Deghost' dropdown with Off / Low / Medium / High. I usually choose Off; only when the scene contains moving objects that produce ghosts after merging do I pick Low, Medium or High according to severity. (In the example below, the boat moved between frames, leaving a translucent ghost after merging.)"},{"t":"img","f":"img-16","w":1000,"h":614},{"t":"p","x":"设置完毕后，ACR已经自动为我们完成了HDR曝光合成，点击“合并”，把3张合成完毕的新文件储存在硬盘上。","b":false,"xe":"With settings done, ACR has automatically performed the HDR blend. Click 'Merge' to save the new combined file to disk."},{"t":"img","f":"img-17","w":1000,"h":895},{"t":"p","x":"之后我们会再次进入ACR软件中，并且看到一张新的合成后的底片（DNG格式）。这张新的底片，包含了原来3张raw文件的全部信息，给后期调整提供了很大的空间。（比如单张raw文件的曝光滑块，我们最多只能加减5档，而HDR合成文件，ACR允许后期加减10档的曝光。）","b":false,"xe":"You then re-enter ACR and see the new merged negative (DNG). It contains all the information from the three original raw files, leaving huge room for adjustment. (A single raw file allows only ±5 stops on the exposure slider; an HDR-merged file allows ±10 stops in ACR.)"},{"t":"img","f":"img-18","w":1000,"h":584},{"t":"p","x":"由于在合并时，我们勾上了“自动色调”，ACR就自动帮我们调整了曝光、高光、黑色等参数。这些都是非破坏性调整，如果我们觉得不满意，可以重新调整这些滑块和参数。","b":false,"xe":"Because we checked 'Auto Tone' during the merge, ACR has already adjusted exposure, highlights, blacks and so on. These are non-destructive — if you're not satisfied, simply re-adjust the sliders."},{"t":"img","f":"img-19","w":1000,"h":818},{"t":"p","x":"比如这张照片，我重新提高了对比度，并进一步降低黑色，提高画面的反差。","b":false,"xe":"On this photo, for example, I raised the contrast again and lowered the blacks further to increase the punch."},{"t":"img","f":"img-20","w":1000,"h":610},{"t":"p","x":"之后的调整就和普通raw文件一样了，镜头校正、变换、调色、局部处理等等，这里就不一一细讲了。","b":false,"xe":"From here on, adjustments are the same as for any raw file — lens corrections, transforms, grading, local work — so I won't go through them one by one."},{"t":"p","x":"（由于HDR合成时，算法会丢弃我们的一些调整，所以推荐大家先进行HDR合成，再进行曝光、调色以及局部的调整。）","b":false,"xe":"(Since the HDR algorithm discards some of your adjustments during the merge, it's recommended to merge HDR first, then do exposure, grading and local adjustments.)"},{"t":"img","f":"img-21","w":1000,"h":605},{"t":"p","x":"最后处理完的成片，窗户内外的细节，都一清二楚。大光比复杂环境，在包围曝光和曝光合成技术下，也变成了小菜一碟。","b":false,"xe":"In the final image, details inside and outside the window are crystal clear. Thanks to bracketing and exposure blending, a complex high-contrast scene becomes a piece of cake."},{"t":"img","f":"img-22","w":757,"h":1000},{"t":"p","x":"欢迎关注@Thomas看看世界，","b":false,"xe":"Follow @Thomas Chu Photo,"},{"t":"p","x":"每周学会一个摄影技能。","b":false,"xe":"and learn one photography skill every week."}],"titleEn":"No More Fear of High Contrast: Exposure Bracketing & Blending Explained"}