{"slug":"color-banding-fix","title":"不要让色彩断层毁了你的照片","author":"Thomas看看世界","date":"2017-02-26","wechat":"https://mp.weixin.qq.com/s?__biz=MzI4NDA5MzE5NQ==&mid=2247485143&idx=1&sn=2ca85133b13cefa0b86f3554eac3ceda&chksm=eb81f8b3dcf671a55316405217ba07e6ba1f640b2e235caa58a26cc643bd5beda7def298d034&scene=21#wechat_redirect","blocks":[{"t":"p","x":"色彩断层在人像拍摄和风光后期中都经常发生，明明应该细腻的渐变过渡，却变成了一块一块的奇怪色带，简直让人崩溃。","b":false,"xe":"Color banding happens often in portrait shooting and landscape post-processing: what should be a silky gradient breaks into strange, blocky bands — enough to drive you mad."},{"t":"p","x":"本文将谈谈色彩断层的成因，以及如何尽量避免、甚至修复它们。","b":false,"xe":"This article discusses the causes of color banding, and how to avoid or even repair it."},{"t":"h","x":"1","xe":"1"},{"t":"h","x":"什么是色彩断层","xe":"What Is Color Banding?"},{"t":"p","x":"不知道大家有没有遇到过下图这种情况，本该很干净的蓝色天空，却断裂成了一层层的色彩带。","b":false,"xe":"You may have encountered the situation below: a sky that should be a clean blue breaks into layer upon layer of color bands."},{"t":"img","f":"img-02","w":1000,"h":606},{"t":"p","x":"这种现象我们把它称为色彩断层（色彩带，color banding），多发生在纯净的渐变物体中，比如黄昏天空，棚拍背景，光线投影等等。","b":false,"xe":"We call this phenomenon color banding. It mostly appears in pure gradient subjects — dusk skies, studio backdrops, projected light, and so on."},{"t":"p","x":"色彩断层的原因，是图像的色彩深度不足以表现微小的渐变，因此本该平滑的渐变变成了下图般一块一块的断层。","b":false,"xe":"The cause: the image's bit depth can't represent the tiny steps of the gradient, so what should be a smooth transition becomes the blocky bands below."},{"t":"img","f":"img-03","w":1000,"h":702},{"t":"p","x":"打个比方，本来平滑的渐变应该是","b":false,"xe":"To illustrate: a smooth gradient should read like"},{"t":"p","x":"0，0.25，0.5，0.75，1，1.25，1.5，1.75，2，2.25，2.5。。。","b":false,"xe":"0，0.25，0.5，0.75，1，1.25，1.5，1.75，2，2.25，2.5。。。"},{"t":"p","x":"但是由于图像色深不够，导致小数无法显示出来，所以上面一串数字就成了","b":false,"xe":"But with insufficient bit depth, the decimals can't be displayed, so the sequence above becomes"},{"t":"p","x":"0，0，0，0，1，1，1，1，2，2，2。。。","b":false,"xe":"0，0，0，0，1，1，1，1，2，2，2。。。"},{"t":"p","x":"色彩断层有时在小图中还不明显。","b":false,"xe":"Color banding is sometimes barely visible in a small image."},{"t":"img","f":"img-04","w":1000,"h":666},{"t":"p","x":"但是在大图中它就会变得特别引人注目。打印过程更会突出这种色彩断层现象，毁掉一张摄影作品。","b":false,"xe":"But in a large print it becomes glaringly obvious. Printing accentuates banding even more, ruining a photographic work."},{"t":"p","x":"为了更好的观察色彩断层现象，我们一般会建立一个solar curve观察曲线。这种曲线长得很像正弦函数，可以夸张的突出局部变化，让摄影师发现很多不容易观察到的瑕疵。","b":false,"xe":"To inspect banding more easily, we usually build a solar curve. Shaped like a sine wave, it exaggerates local changes and reveals many flaws that are otherwise hard to see."},{"t":"p","x":"比如这张图片建立正弦观察曲线后，就突显出了好几个很难察觉的脏点。","b":false,"xe":"This image, for instance, reveals several barely noticeable dirty spots once the sine inspection curve is applied."},{"t":"img","f":"img-05","w":1000,"h":995},{"t":"p","x":"正弦观察曲线下的照片天空，渐变断裂的情况非常明显。","b":false,"xe":"Under the sine inspection curve, the broken gradient in the photo's sky becomes unmistakable."},{"t":"img","f":"img-06","w":1000,"h":633},{"t":"h","x":"2","xe":"2"},{"t":"h","x":"如何尽量避免色彩断层","xe":"How to Avoid Color Banding"},{"t":"p","x":"上面提到过，色彩断层的成因主要是图像色彩深度不够。色深越低的图像，原始信息越少的图像，比如8位的JPEG，运算时越容易出现断裂的渐变带。","b":false,"xe":"As mentioned, banding mainly comes from insufficient bit depth. The lower the bit depth and the less original information — an 8-bit JPEG, say — the easier gradients break during computation."},{"t":"p","x":"因此我们前期应当尽量使用无压缩或者无损压缩的raw格式拍摄。光比很大的时候，尽量包围曝光再后期合成，而不是单张高光-100。","b":false,"xe":"So in the field, shoot raw with uncompressed or lossless compression whenever possible. In high-contrast scenes, bracket exposures and blend in post rather than dragging a single frame's highlights to -100."},{"t":"p","x":"后期处理时，能在ACR、Lightroom等Raw处理器中进行的调整，就不要推迟到Photoshop中再操作，尽量利用raw文件的强大信息量。","b":false,"xe":"In post, do every adjustment you can inside a raw processor like ACR or Lightroom rather than postponing it to Photoshop — make the most of the raw file's rich information."},{"t":"p","x":"Raw处理器进入PS时，使用16位的色彩深度。在ACR中，你只需要点击界面最下面的一栏字，然后在弹出的设置面板中，把色彩深度调整为“16位/通道”。","b":false,"xe":"When moving from a raw processor into PS, use 16-bit depth. In ACR, click the line of text at the very bottom of the interface, then set Color Depth to \"16 Bits/Channel\" in the dialog that appears."},{"t":"img","f":"img-07","w":1000,"h":866},{"t":"p","x":"这样我们在从ACR进入PS的过程中，raw文件会被转化为16位的图像，标题栏最后会显示“RGB/16”，而不是8位图像的“RGB/8”。","b":false,"xe":"That way the raw file becomes a 16-bit image when it enters PS, and the title bar will read \"RGB/16\" instead of the 8-bit \"RGB/8.\""},{"t":"img","f":"img-08","w":1000,"h":767},{"t":"p","x":"在raw文件和16位图像中操作，可以大大减缓色彩断层的发生，却也无法完全避免。有的时候后期压暗提亮、HSL调整、降噪等操作，无可避免的还是会产生断层，只有再用其他的办法修复了。","b":false,"xe":"Working in raw and 16-bit greatly slows the onset of banding but can't prevent it entirely. Darkening, brightening, HSL adjustments, and noise reduction will inevitably cause banding at times — and then we repair it by other means."},{"t":"h","x":"3","xe":"3"},{"t":"h","x":"如何修复色彩断层","xe":"How to Fix Color Banding"},{"t":"p","x":"图像领域我们可以用仿色（Dithering）的办法来掩盖色彩断层。","b":false,"xe":"In imaging, we can use dithering to mask color banding."},{"t":"p","x":"所谓仿色就是仿造颜色，主要目的是用较少的颜色，来表达较丰富的色彩过渡。仿色使渐变中的各种颜色不再是一个个生硬的色块，而是互为交融渗透，这样在人眼的整体视觉效果中就会形成平滑、自然的过渡，就像是自然条件下人看到的颜色一样（百度百科）。","b":false,"xe":"Dithering means simulating colors: its purpose is to express richer color transitions with fewer colors. Dithering makes the colors in a gradient blend into one another instead of sitting in hard blocks, so the human eye perceives a smooth, natural transition — just like colors seen in nature (Baidu Encyclopedia)."},{"t":"img","f":"img-09","w":1000,"h":432},{"t":"p","x":"比如上面的渐变，右边的图像和左边一样，都只使用了4种颜色。但左边各个颜色间边界分明，过渡断层就很明显。右边由于我们在过渡带把几种颜色混合在了一起，视觉上看起来就平滑多了。","b":false,"xe":"Take the gradient above: both the left and right images use only four colors. On the left the boundaries are hard and the banding obvious; on the right, the colors are mixed in the transition zones, so it looks far smoother."},{"t":"p","x":"那么我们如何在Photoshop中模拟仿色运算呢？","b":false,"xe":"So how do we simulate dithering in Photoshop?"},{"t":"p","x":"大家仔细观察一下，仿色过渡中的一个个小颗粒，是不是有点像摄影师们的一位老朋友？","b":false,"xe":"Look closely at the little grains in a dithered transition — don't they remind you of an old friend of photographers?"},{"t":"img","f":"img-10","w":1000,"h":896},{"t":"p","x":"没错，那就是噪点！","b":false,"xe":"That's right — noise!"},{"t":"p","x":"所以听起来有些不可思议。要解决色彩断层问题，我们只需要往照片中相应的区域，加入颗粒噪点就行了。","b":false,"xe":"Incredible as it sounds, solving color banding only requires adding grain noise to the affected area of the photo."},{"t":"p","x":"模拟仿色的加噪方式有很多。包括“滤镜 - 杂色 - 添加杂色”、“滤镜 - 滤镜库 - 喷溅”，“滤镜 - Camera Raw滤镜 - 颗粒”等等。我比较喜欢用最后一种方法。","b":false,"xe":"There are many ways to add noise to simulate dithering: Filter > Noise > Add Noise, Filter > Filter Gallery > Spatter, Filter > Camera Raw Filter > Grain, and so on. I prefer the last one."},{"t":"p","x":"首先按住Ctrl+Alt+Shift+E（苹果键盘Command+Option+Shift+E）盖印可见图层，然后打开“滤镜 - Camera Raw滤镜”。","b":false,"xe":"First, press Ctrl+Alt+Shift+E (Command+Option+Shift+E on Mac) to stamp visible layers, then open Filter > Camera Raw Filter."},{"t":"img","f":"img-11","w":660,"h":564},{"t":"p","x":"打开第七个面板 - “效果”面板，找到“颗粒”一栏，往右拖动“数量”滑块。拖动时密切注意图像，你会发现照片中颗粒越来越多，慢慢的色彩断层就几乎消失了。这张图像，我的增加颗粒数量大概在20左右。","b":false,"xe":"Open the seventh panel — Effects — find the Grain section, and drag the Amount slider right. Watch the image closely as you drag: grain gradually increases, and the banding nearly vanishes. For this image, I set Amount to about 20."},{"t":"img","f":"img-12","w":1000,"h":976},{"t":"p","x":"点击完成后放大图片，你会发现原来干净的天空中多了很多颗粒。","b":false,"xe":"Click OK and zoom in: the once-clean sky now carries a good deal of grain."},{"t":"img","f":"img-13","w":1000,"h":748},{"t":"p","x":"不过好在色彩断层几乎看不见了，即便在正弦观察曲线下，天空过渡也很平滑。","b":false,"xe":"But the good news is the banding is nearly invisible — even under the sine inspection curve, the sky's transition is smooth."},{"t":"img","f":"img-14","w":1000,"h":589},{"t":"p","x":"当然天空中的颗粒感太突兀了一点，我又打开“滤镜 - Camera Raw滤镜”，然后在第三个细节面板中，增加“减少杂色 - 明亮度”滑块的值到60，让照片中的颗粒不要太明显。（这步并不是要消除颗粒，否则我们的色彩断层又会回来了，而是让颗粒更好的融合在天空中，不要太明显。）","b":false,"xe":"The grain in the sky was still a bit abrupt, so I reopened Filter > Camera Raw Filter and, in the third Detail panel, raised Noise Reduction > Luminance to 60 to make the grain less obvious. (This step isn't about removing the grain — that would bring the banding back — but blending it into the sky more naturally.)"},{"t":"img","f":"img-15","w":812,"h":1000},{"t":"p","x":"完成之后的效果（观察曲线下）。左边是处理前的断层天空，右边是处理后，过渡看起来平滑多了。","b":false,"xe":"The result (under the inspection curve): banding sky on the left before, much smoother transition on the right after."},{"t":"img","f":"img-16","w":1000,"h":642},{"t":"p","x":"最后一步，建立蒙版，让刚刚的操作只作用在有色彩断层的天空上，而不影响地面的细节。","b":false,"xe":"Final step: add a mask so this treatment applies only to the banded sky, leaving the ground's detail unaffected."},{"t":"img","f":"img-17","w":1000,"h":677},{"t":"p","x":"下面是另外一张类似的照片。","b":false,"xe":"Below is another, similar photo."},{"t":"img","f":"img-18","w":1000,"h":881},{"t":"p","x":"添加颗粒前的天空（观察曲线下），断层惨不忍睹。","b":false,"xe":"The sky before adding grain (under the inspection curve) — the banding is dreadful."},{"t":"img","f":"img-19","w":1000,"h":782},{"t":"p","x":"添加颗粒之后（观察曲线下），过渡看起来自然多了。","b":false,"xe":"And after adding grain (under the inspection curve) — the transition looks far more natural."},{"t":"img","f":"img-20","w":1000,"h":778},{"t":"h","x":"总结","xe":"Summary"},{"t":"h","x":"1. 后期处理时，天空、背景等渐变区域很容易出现色彩断层现象。","xe":"1. In post-processing, gradient areas like skies and backdrops are prone to color banding."},{"t":"p","x":"2. 使用Raw格式拍摄，尽量在Raw处理器中修图，以及使用16位色深，可以延缓色彩断层的发生。","b":true,"xe":"2. Shooting raw, editing inside raw processors, and using 16-bit depth all delay the onset of banding."},{"t":"h","x":"3. 我们可以用Camera Raw滤镜-添加颗粒的办法，后期掩盖住色彩断层。","xe":"3. We can mask color banding in post with the Camera Raw filter's Grain."},{"t":"p","x":"欢迎关注@Thomas看看世界，每个周日，学会一个摄影技能。","b":false,"xe":"Follow @Thomas Chu Photo, and learn one photography skill every Sunday."},{"t":"img","f":"img-21","w":640,"h":313}],"titleEn":"Don't Let Color Banding Ruin Your Photos"}