Red Epic HDRx 测试

2011-06-09 12:18

#大画幅可换镜头# #设备体验#

这文章如果我没有判断错的话应该算是EPIC的首测了吧。

ps：此文中不可控词汇有些多，错误请指正哈。
这是一个5K RED Epic数字电影摄影机的测试，机器是找Blair Paulsen借的，那是第一批可用的EPIC其中一台。除了其高分辨率传感器外，还有一个新玩意儿是“HDRx”，是一种具有创造性的事物在数字摄影机一直缺乏的：高动态范围。 
Epic HDRx 测试（抱歉，测试是含有测试视频了，但使用中国互联网的弟兄们都看不见。）
Epic的传感器在非HDRx状态下已经可调至11到13的曝光范围。在HDRx状态下，你会得到一个完全独立的曝光，2至6档捕获的会比原来的暗。它的工作原理是这样的：摄像机呈现适当的快门速度1/48秒，在那情况下快速曝光，然后再在1/96秒或者更短。之后会在视频文件夹R3D里会含有两个单独的视频轨道，“A”和“X”不同曝光：一个暗部细节很好，一个高光部分保留得很好。 
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将这两个单独轨道做一个后期处理，用快速的方法，可以是RED超速卡，可以利用自带软件，如Assimilate Scratch。 RedCineX有一个不错的混合模式，你可以将两种数据淡化混合直到你觉得不错。这个实验随便能够超越简单的透明度混合，这个HDRx最终图像看起来多好，使用更多复杂的技术。 
HDRx在Scratch中使用其实非常简单。你导入R3D，你有一个选择是“A track” 0 或者“X track”1。将第二轨拖到工程中，你选择如何组合它们。 
选择使用亮度项，将X track放在上面切断图像中的暗部，然后逐渐变化两个图像，然后你能看到当一个视频轨停止的时候另一个接管了。这样可以很快的合并，巧妙处理大部分的图像，使你满意。当然，图像会在一时间有稍微的不同，和一些ammounts运动模糊一样。如果拍摄了很多运动和硬边，那么你可能会看到一些人工痕迹。在这种情况下就使用软件解决方案，以增加运动模糊感到X-track，让他们更好混合。 
这里有一些图（16位未压缩的TIFF）来比较。他们被缩放到2K，也许以后我可以弄些5K的版本。在原文最下面还有一些ProRes 4444的文件。
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（这里只是一些截图，原文链接里点击图后有真正的2k图，大家可以去看）
http://blog.localheropost.com/ RED EPIC
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可参照原文：
The last week has been a whirlwind of testing Red\\\\\\\\\\\\\\\'s new 5K Epic digital cinema camera, special thanks to Blair Paulsen for lending us his camera, one of the first Epics available. Beyond its high resolution beautiful sensor, the new kid in town is called \"HDRx,\" and is a creative take on something that digital cameras have lacked for awhile: High Dynamic Range. 
 Leandro put together a video summing up our tests, check it out on Vimeo:
Local Hero Epic HDRx Test from Local Hero Post on Vimeo.
The Epic sensor without HDRx is already in the 11 to 13 stop range, depending on who you ask.  With HDRx, however, you get an entirely separate exposure, 2 to 6 stops darker than your original capture.  How it works is this:  the camera exposes a proper shutter speed of 1/48 of a second, and then right after takes a quick second exposure at a fraction of that, say 1/96 of a second or shorter.  What you get on your R3D files afterward is a video file that contains two separate video tracks, \"A\" and \"X\" of the different exposures: one with better exposed shadows, and one with better exposed highlights.
Processing these two separate tracks into something usable is a job for the post process, using a fast system, perhaps a Red Rocket card, and the software that can take advantage of it natively, like Assimilate Scratch.  RedCineX has a nifty little blending mode, where you can slide between the two streams and fade them together until you\\\\\\\\\\\\\\\'re happy.  We at Local Hero, however, did a little experimenting on our own to move beyond simple opacity blending, to see how good we could get an HDRx final image to look using more complex techniques.
The HDRx implementation in Scratch is pretty simple.  When you bring in your R3D you have the choice to show either the \"A track\" 0 or the \"X track\" 1.  Drag the second track into a scaffold layer, and you can choose how to combine them.
We chose to use a Luma Key, where you lay the X track on top and key out the darker areas of the image, then grade both images so that you can\\\\\\\\\\\\\\\'t see where one video track leaves off an the other takes over.  This can come together quickly, or be finessed quite a bit to make an image that you\\\\\\\\\\\\\\\'re happy with.  True, the images are slightly different temporally, as well as exhibiting different ammounts of motion blur.  If your shot has a lot of motion and hard edges, then you may see some artifacting.  In these cases there are software solutions to add motion blur back into the X-track to help them blend better. 
Here are some stills (with uncompressed 16 bit TIFF links available) to compare on your own.  They are scaled to 2K, perhaps I can get a full 5K version up in the future.  Down at the bottom are some ProRes 4444 files as well.  
本文为作者 李害害 分享，影视工业网鼓励从业者分享原创内容，影视工业网不会对原创文章作任何编辑！如作者有特别标注，请按作者说明转载，如无说明，则转载此文章须经得作者同意，并请附上出处(影视工业网)及本页链接。原文链接 https://cinehello.com/stream/1712