lab色彩空间一书各章节总结 4
In all these cases thus far we let one thing to be the same: all ourcurves were always going through the same original center point (0A0B).Now it's time to see what happens if we unlock this magic point of thismysterious space./e9} z(R4da@z,v(Z/G#` t
As you figured out, Chapter 4 dead centers on "center point".
[b]First of all, executive version: [/b]
[b]1) you need to move A or B curves off center if your image has a "cast".[/b]
[b]2) you need to add a "center point lock" if you need to modify"halves" independently, for instance adjust red (i.e. magenta) butleave green intact (or apply independent green tweak).[/b]
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Following the brave pioneers of this discussion (Rutt and DavidTO) I'mgoing to provide my own image and try to follow the brilliance of theauthor.
My first obstacle was to find a casted image that would carry enoughfamiliar patterns to recognize the problem and would be joy to fix. Iwas trying to remember when was the last time I forgot to switch whitebalance from incandescent to auto:-), but nothing came to mind. FinallyI decided to cheat and use of of the RAW files (in which I could spoilthe white balance - hey, it's for the better good!).
Here's an example we'll be working with:
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[attach]50315[/attach]
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This picture was taken during my May trip to Yosemite, when I met withSid and Michiel in SF. This is actually how 828's RAW data wererecorded, so I didn't even have to spoil it on purpose. As it's easy tosee, this picture features certain yellow cast.
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I started with exploring the picture. As it was said before me, LAB isall about to make the picture closer to what you THINK you saw. Also,one of Dan's mantras says: "don't give them colors they wouldn'tbelieve". So I put my markers on the 4 most visually important coloredareas:5^/Kxy)E C
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Here's how info looked on our markers:
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[attach]50317[/attach]
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It's easy to see that both clouds (#1) and water (#4) have positive Bvalues (yellow), while they, generally speaking, should have hadnegative (blue) ones - it was a clear morning after a rainy night, airshould not have added any yellow cast to the clouds.h'W!N N9X$Y
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Following Dan's advice, I decided not to concentrate on potentiallyneutral points. Landscape photographers know only too well that thereis no such thing as 100% reliable neutral color in nature. Clouds couldtake whatever color sun decides to throw at them, skies can be anythingfrom deep blue (up in the mountains) to pale green (way up North),water, even if not colored by some minerals, reflects both skies andclouds..b0TfS,{I'^
So I dropped the idea of "betting" my image on anything and simply tookoff with what I thought was right (supported by some channel info:-).$Y$V!_\-H*Xvo K"^
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First I made sure that I need to offset only one curve, namely B, sinceB controls Blue-Yellow and the image is yellowish. Simple tweaking thecenter of A both ways proved me right: any move away from center pointmade the cast worse.
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After playing a little with B I reached "believable" blueness of thewater (#4) while keeping sky (#2) and clouds (#1) also quite natural.?N5wuC&n
My last stop was marker #3 - the Golden Gate Bridge itself. There wasno scientific info on its color, but I *thought* it was less orange andmore magenta. However, I already knew that if I make any change to thecenter point I'll introduce a new cast. Therefore I used the Trick No 2and locked the A-curve in the middle, which allowed me to experimentfreely with the red hue.
After I added a bit more contrast to L channel by making a pretty much standard S-curve, my curves ended up looking like that:8|OH L#e`
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And my new marker info looked like follows (new data below, I kept the original info on top for an easy comparison):kP'qx3~Z'o"i\
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As it's easy to see, B values #1 and #4 were changed in a most drasticmanner - they "crossed the border" and moved from Yellow Country toBlue Country.
Here is the final image:
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[attach]50320[/attach]
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And, for another easy comparison, half-blended version:h q Z2sj u:c
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The difference is quite obvious, and, I'd say, the final version is much closer to what I saw that lovely morning.+dq(R2?;HXR
[SNIDE REMARK]
Actual editing in RAW without any LAB magic gives you this::?s3_2V C6L#A6m3H%Wl
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which, to my taste, is even closer to "my reality" than myLAB-processed version. So, my take on this: if you have RAW - by allmeans, use it first! hJW"eZ q JP1Z4u
However, if you don't - LAB can give you a good hand in cast correction.
Besides, when it comes to independent color adjustment (trick #2) - LABis a hands down winner, since raw editors cannot do this (yet).
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OK, what did we learn?|"gvEY&uY
We learned to remove the cast (offset the curve away from center), andwe also know how to fix one color without affecting its counterpart(lock the curve in the middle).
[[i] 本帖最后由 honghu 于 2007-3-11 16:51 编辑 [/i]] 就看懂了1,后三个没明白 honghu老师的贴子一定要看，但偶的E文，不太好，光看图又不理解意思，希望老师加以汉化:( 俺理解用Lab格式可以校正色温，当你没有RAW的时候:lol 看图勉强看懂了一点
然后拿翻译软件翻译英文
看了觉得莫明其妙···还不如看原文·· @ r:z F J^,P|
如果可以的话,希望能够有汉化的版本 ] ]3wP@
至少重要的地方汉化一下···/n3E:[ }hr
对于E文苦手,看这些东西实在是一种折磨 哇``大哥```不懂E文哦``光看图``哇噻``太神了``看字``嘿嘿``七个懂了六个-----一个不懂3e6G!?F/{K
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[[i] 本帖最后由 唏哩哗啦 于 2007-6-3 22:50 编辑 [/i]] :( 勉强看懂了点点.调了一个. - -.
[img]http://image.pengpeng.com/repository/06/130/203/album/200706/20070604011531427.jpg[/img] 晕，真是强啊，我一知半解。
我的RGB
[localimg=400,300]1[/localimg]我的RGB
[attach]71105[/attach] 处于看图说话状态，能不能弄个中文的来？ 我也试了下好象还可以做红外效果咯
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