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游戏开发团队运用动作捕捉技术的10个要点

发布时间:2012-07-09 14:08:33 Tags:,,,,

作者:Tristan Donovan

动作捕捉技术在过去数十年取得了很大进步。摄像机变得更为平价,而软件也更为出色,甚至是眼动追踪技术也不再是无法攻克的难题。在此期间,动作捕捉技术也在游戏中更为普遍,甚至可以说它在大型主机游戏中比手部动画更常见。

但一次成功的动作捕捉拍摄与一堆无用的数据之间的区别究竟在哪?你要用什么技术最大化地捕捉演员的动作?什么时候你根本无法使用训练有素的演员?

我们将通过本文与《光晕:致远星》、《神鬼寓言3》、《全面战争:幕府将军2》、《狙击精英V2》等游戏背后的动作捕捉人员探讨这些内容。

mocap_halo reach(from gamaustra)

mocap_halo reach(from gamaustra)

1.准备充分

准备充分可以说是所有参与动作捕捉的人员都认同的一个建议。Bungie技术电影艺术主管Kurt Neil表示,他对于成功捕捉动作和表演的最重要建议就是确保一切准备就绪。

“在你踏进摄影棚的时候,全组工作人员都满怀期望地看着你,都需要知道你要拍摄什么内容。这样你才可以省下大把时间,而不至于不知如何应对大家提出的大量问题。”

Creative Assembly(代表作是《全面战争》等游戏)动作捕捉经理Pete Clapperton补充道,最好提前制定交流规则。“在拍摄过程中一般都会有很多人在现场,最好确保所有人都知道自己当天该扮演什么角色,不要让大家因手足无措而失去方向。这其中的主要角色包括运行系统的人员,查看标记的人员以及导演——现场还有其他人,但他们都应该知道何时闭嘴。”

2.用动画来节省时间

在《狙击精英V2》期间,Rebellion Development公司一直到等到游戏通过第一道标准才转入动作捕捉阶段。其主动画师Zsolt Avery-Tierney表示,“这种做法有利于我们探索动画风格,并快速应对项目发展过程中的设计和代码需求变化”。这意味着他们无需将时间和资金浪费在搜集多余或不兼容的动作捕捉数据上,团队在进入拍摄阶段时心里就已经有一个清晰的概念。

他解释到,“在《狙击精英V2》中,我们从演员身上所捕捉的一切内容,事先都已经由我们的动画人员定义和设计好了。这不但有助于大家在拍摄当天更好地沟通想法,还可以确保动画人员保留其权力,把握最终动作捕捉结果。”

另一个好处在于,由于事先定义好这些内容,Rebellion就可以提前告诉动作捕捉工作室关于自己的具体道具需求和尺寸,“这可以最大化当天的时间使用率,极大减少资源浪费现象,减轻动画团队的工作量。”

3.考虑现实世界的解决方案

Bungie动作捕捉主管Troy McFarland表示,“在这个行业的许多情况下,人们常会试着用虚拟解决方案来应对现实世界的问题。”

“服装、道具或场景的一点小改动往往有可能更好地帮助我们捕数据,并让动作演员更好地融入场景和表演中。在《光晕:致远星》早期镜头中,我发现动作捕捉数据中的手部旋转并不如真人演员视频中那样频繁。”

“深入观察后,我发现是我们的服装出了点问题。它们是从肩膀到关节连接起来的布片,我就让动作捕捉服装供应商为我们定制了袖子更短的服装,以及带有额外布片的手套,这样我们就可以在手腕处做标记。这个改变的效果明显,并且这些衣服也因此更适用于广泛的演员群体。”

4.演员并不需要有动作捕捉经验

自由职业演出导演Kate Saxon(曾参与作品包括《神鬼寓言:旅途》以及《詹姆斯邦德007:血石》)表示,许多人误以为针对游戏的动作表演与电影或舞台演出并不相同。

据她所称,“演员通常要针对相应媒体进行一番训练,游戏行业有个误解就是,游戏与其他媒体多少有点不同,所以你只能使用那些已经拥有动作捕捉表演背景的演员,但这实际上非常荒谬。”

“有时候人们认为要进行动作捕捉,就需要使用肢体表演者,但演员本身就是肢体表演者,他们已经习惯使用整个身体、脸部和声音来完成整个表演。”

mocap_fable3(from gamaustra)

mocap_fable3(from gamaustra)

5.不要忽视全动作捕捉

动作捕捉工作室House of Moves业务开发经理Jimmy Corvan表示,进行电影艺术性质的全动作捕捉需要投入额外精力和开销,这样你才能捕到演员最具人性化的瞬间。

“传统做法是让配音演员进入控制室,让他们把台词背个三四遍,直到能够流顺表达为止,然后再让另一个演员上动作捕捉台配合前者解说的动作,直到完美表现出来为止。”

“然后就是让动画人员将一切内容结合起来,让整个镜头呈现完美状态。但人类不可能总是完美表现一切状态,你在全动作捕捉中得到的一些细微瑕疵实际上更能体现人性化特点,例如演员疲劳地说话时的那种略为拖拉的状态。

6.制作立体道具

道具虽然有利于演员更好地表现动作,它们也可能挡住动作捕捉标记。McFarland表示,”在《光晕:致远星》制作早期,我们使用与真枪等比例仿制并具有重量的枪支,但这会产生两个问题。首先,它们会挡住演员胸前的标记并延长清理过程,导致动作的延期交付。其次,与肩部有关的手势位置也会因这些假枪而遁形。”

为解决这个问题,McFarland根据游戏中的枪支截图为演员制作了一支立体步枪。“我组装这个玩具枪道具有两个原因。第一,玩具枪已经有一个适合握住的形状,这就为我省下了仿造手柄的时间。第二,它有一个可以活动的扳机,可以让演员获得一种活动感,他们在表演时就可以扣动这个扳机。”

7.并非所有演员都必须是“演员”

你可以根据自己的需求,选择相应的表演者来担任演员。Creative Assembly在制作《全面战争:幕府将军2》过程中就找了一些非动作领域的人员来扮演武士。据Clapperton所称,“我们这款游戏要找的是有武术背景的人,所以就找到了英国奥林匹克剑术队运动员来做这些事情”。

“但我们发现他们的动作和表演非常准确,看起来像是规范处理后的结果,而我们要找捕捉的是一些在混战中打斗的动作,所以我们不得不让他们打破常规,不过他们还是比较愿意我们提供一些明确方向。”

8.指导要准确而具体

Saxon表示,向演员详细说明要求这一点不容忽视,“我最近正投入制作一款暂时无法公布的游戏,在这个过程中我经常和特技人员打交道。我发现他们经常抢打,所以我不得不向他们说明一些肢体选择要求,告知他们这个角色打斗时并不像个训练有术的战士,而是像出身草莽的街头霸王。”

“特技人员欣然接受了这个提议,但如果没有人指出这一点,最后就会发现玩游戏时,所有人突然之间都陷入一场动作机械的格斗中。”

mocap_sniperv2(from gamasutra)

mocap_sniperv2(from gamasutra)

9.相信参与人员的专业水准

来自Bungie的Nellis表示,“理想情况下,在摄影棚中的所有人(包括演员在内),都很清楚自己的工作职责。当一名动作捕捉技术人员向你提出问题时,要注意倾听。他们可能会告诉你一个重要的坏消息,但最好马上着手解决问题而非事后再去寻找无用的数据。假如有演员声称自己对上一次拍摄觉得不对劲,不过可以将它放到下一组拍摄时,你可能会发现他们的说法正确极了。你并不一定总会接受他们的建议,但最好要尊重这些工作人员的专业技能。只有得到尊重的人员才会卖力为你工作。”

10.确立资产命名惯例

Rebellion的Avery-Tierney表示,确定一个动作捕捉资产的明确命名系统可以提高大家的沟通效率,“在《狙击精英V2》制作过程中,因为我清楚自己要用的姿态、方向,所以对素材也依此命名,这让我们在拍摄时更有方向感,也更便于回顾连续镜头并选择内容,不致于让我们因过于冗长或复杂的命名系统而陷入混乱无序的状态”。

“例如在‘walk_forward_jump_to_mantle_walk_jump_back_down’这个文件名称中,虽然它包含了许多内容,但也含有一些我如果不重新查看就可能会错过的元素。假如是我为这个资产命名,我可能会将它称为‘StepUp_JumpDown_Fidgets_01’并允许最后一个字段带有模糊性,这样可以促使我过后深入探究其中内容。”

“如果那是我指导拍摄的内容,我至少会捕捉或至少是选择将每个动作视为一个独立资产。因为这符合我在项目开发过程中对这些内容的使用方式,也可以节省一些处理成本,提高动画团队寻找并利用资产的效率。”(本文为游戏邦/gamerboom.com编译,拒绝任何不保留版权的转载,如需转载请联系:游戏邦

10 Tips: Getting the Most from Motion and Performance Capture

by Tristan Donovan

[In the second of Gamasutra's discipline-specific series gathering important tips and techniques direct from developers, Tristan Donovan delves into motion and performance capture. You can read his prior article on audio, here.]

Motion capture technology has come a long way in the past decade. Cameras are cheaper, the software is better, and even the challenges of tracking eye movements are being overcome. At the same time, motion capture has also become more commonplace in games — so much so that it’s more common to see motion capture than hand animation in most big-name console titles.

That’s all well and good, but what makes the difference between a successful motion capture shoot and a mountain of useless data? What techniques allow you to get the most out of your actors — and are there times you shouldn’t even use trained actors at all?

In this feature we ask the motion capture pros behind games such as Halo: Reach, Fable III, Total War: Shogun 2 and Sniper Elite V2 for their nuggets of mo-cap wisdom.

1. Prepare, prepare, prepare

If there’s one single piece of advice that everyone involved in performance capture agrees on it’s that preparation is everything. “Of all the advice I have for successful motion and performance capture, this is the most important,” says Kurt Nellis, the technical cinematic lead at Bungie.

“Before you set foot in the room with your talent suited up and the crew looking at you expectantly, know what you are shooting. It saves a tremendous amount of time, as you won’t be caught with your pants down because you don’t know the answers to the questions everyone will undoubtedly have on set.”

Bungie’s Halo: Reach

Pete Clapperton, motion capture manager at Creative Assembly, the studio behind the Total War games, adds that it’s good to set out the rules of communication in advance, too. “During the shoot there’s normally a lot of people, and it’s always a good idea to make sure everybody knows exactly what role they are playing on the day, because you don’t want three people giving directions. The main roles are the person working the system, the person watching for any markers that fall off, and the director — there are other people, but they need to know when to shut up.”

2. Save time with animation

When making Sniper Elite V2, Rebellion Developments waited until the game reached first pass standard before turning to motion capture. “This allowed us to fully explore the style of the animations and react quickly to the evolving design and code requirements as the project progressed,” says lead animator Zsolt Avery-Tierney. This meant time and money wasn’t wasted on collecting redundant or incompatible motion capture data and that the team entered the shoot with a clear idea of what they wanted.

“Everything in Sniper Elite V2 that we gained from our actors was initially defined and designed by our animators. This not only served better communication on the day but also ensured our animators retained ownership and remained devoted to the final delivery,” he explains.

Another benefit was that because the content was already well defined, Rebellion could tell its mo-cap studio its exact prop requirements and measurements in advance: “This maximized time usage on the day, drastically reduced asset waste, and relieved the third pass burden on the animation team.”

3. Think about real-world solutions

“Many times in this industry, people try to come up with virtual solutions to real world problems,” says Troy McFarland, motion capture lead at Bungie.

“Often, a simple change in a costume, prop or set will enable us to capture better data and make it easier for the talent to get into the scene and act. On the early shoots in Halo: Reach, I noticed that the hands in the mo-cap data weren’t rotating as much as they were in the video reference of the actual talent.

“On closer examination, I found that our suits were causing the problem. They were one piece from shoulder to knuckle. I had our mo-cap suit vendor create a custom suit for us that had shorter sleeves and gloves with extra fabric where we could place the wrist markers. The result was dramatic and a nice side effect was that the suit could be worn by a wider range of talent.”

4. Actors don’t need previous mo-cap experience

Freelance performance director Kate Saxon, whose credits include Fable: The Journey and 007: Blood Stone, says many assume wrongly that acting for a game is different from film or stage performances.

“Actors are trained to adapt their skills to the medium they are working in and there’s a misconception in the games industry that games are somehow very different and you can only use actors that have already done performance capture, which is utter nonsense,” she says.

“Sometimes people assume that for motion capture they need a physical performer, but actors are inherently physical performers, who are used to doing a whole performance using their whole body, face and voice.”

5. Don’t dismiss full performance capture

Jimmy Corvan, business development manager at motion capture studio House of Moves, says that when it comes to capturing cinematics full performance capture is worth the extra effort and expense — so you can capture the actors at their most human.

“The traditional way is you send a voice actor into the booth, and they recite the lines three or four times until they get the delivery perfect, and then you take another actor onto the motion capture stage to act it out until it’s perfect,” says Corvan.

“And it’s then up to the animators to blend everything together so that the scene looks perfect,” he says. “But humans don’t operate on the perfect level, and what you get in full performance capture is the small nuances of imperfection that actually make us human, such as the draw on the words the actors say as they become more exhausted.”

6. Make wireframe props

While props can help produce better performances by actors, they can also get in the way of the motion capture markers. “Early on in Halo: Reach, we were using realistically proportioned and weighted guns,” says Bungie’s McFarland. “These posed two problems. First they blocked the chest markers resulting in longer clean up and delayed delivery of the moves to the team. Second the hand positions relative to the shoulder were off from those of our purely fictional rifles.”

To tackle the problem McFarland fabricated a wireframe rifle for the actors to use that was based on the screenshots of the in-game gun taken from Maya. “One thing to note with this prop is that I incorporated a toy gun for two reasons. One: the toy gun already had a comfortable grip and not needing to fabricate a handle saved me a lot of time. Two: it had a working trigger and, as silly as this seems, it helps an actor to have a moving, clicking trigger when they work on a scene.”

7. Not all actors need be actors

Depending on your needs, actors might not be the performers you need. For Shogun 2: Total War, Creative Assembly looked beyond the acting world for people to play its samurai warriors. “We required people who were relevant to the martial arts for Shogun 2, so we had Britain’s Olympic Kendo team come in to do some stuff for us,” says Clapperton.

This did mean a bit more direction was necessary, though. “We found that the way they did their movement and performance looked processed because it was very accurate and correct, whereas we were looking for people fighting in the middle of a battle, so we had to ask them to step out of their comfort zone — but they were happy to take direction.”

8. Be specific when directing

It’s important to be clear what you want from actors, says Saxon. “I’ve been working on a game recently that I can’t name, where I’ve been very involved with the stunts,” she says.

“The character has that attitude where their chin juts out, and they are always vying for a fight, and I have to explain those kind of physical choices to the stuntman — and that the way this character would fight wouldn’t be like a trained military person, but like a street fighter where it’s more messy and muddy, more erratic.

“The stuntmen are great at taking this on board, but the danger is that without somebody pointing that out, you can get into a fight when playing the game and suddenly everyone’s behaving like trained fighters.”

9. Trust the people at the shoot

“Ideally, everyone in the room, including the actors, is there because they are good at what they do,” says Bungie’s Nellis. “When a mo-cap technician comes to you with a problem, listen. They may have bad news about the best take you’ve ever captured but it’s better to address it now than find out you had unusable data later. If an actor says they didn’t feel right on that last take and they think they can nail it on the next one, you’ll often be amazed at how right they were. You won’t always be able to take their advice, but the crew will definitely appreciate that their expertise is being utilized. An appreciative crew is a crew that will work hard for you.”

10. Establish naming conventions

Defining a clear system for naming your motion capture assets improves communication, says Rebellion’s Avery-Tierney. “In Sniper Elite V2 I knew my stances, motions, and directions, so my naming followed suit. This gave us a good focus and precision in our takes, made reviewing footage and making selections much easier, and stopped us getting muddy with overly long or complex naming,” he says. “For example ‘walk_forward_jump_to_mantle_walk_jump_back_down’.

“Although the terminology conveyed a lot of content, the take also contained many fidgets that I would have missed if I had not gone back to review it. If I had named the asset I would have called it ‘StepUp_JumpDown_Fidgets_01′ and allowed the ambiguity of the last term to encourage further investigation.

“If I had conducted that shoot I would have captured, or at least chosen, each action as separate assets. This is because that’s how I would have used them on project, saving valuable seconds of processing cost, and increasing the efficiency of the animation team to find and turn around assets from their schedule.”(source:gamasutra


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