That happens because these works employ a technique called anamorphosis.

這是因為，這些作品都採用一種稱為「變形」的技術

Anamorphosis is a special case of perspective art, where artists represent realistic three-dimensional views on two-dimensional surfaces.

所謂的「變形」是視角藝術的一個特例，是藝術家在二維的平面上，展現逼真的三維視圖。

Though it's common today, this kind of perspective drawing has only been around since the Italian Renaissance.

儘管今日看來，它很稀鬆平常，但這種透視畫法卻是自義大利文藝復興以後才開創的。

Ancient art often showed all figures on the same plane, varying in size by symbolic importance.

古代藝術經常在同一個平面上顯示所有人物，藉由大小的變化來象徵重要性。

Classical Greek and Roman artists realized they could make objects seem further by drawing them smaller, but many early attempts at perspective were inconsistent or incorrect.

古希臘和羅馬藝術家意識到，他們可以使物體看起來遠離一點，只要藉著把他們畫小一點，但早期不少這種遠景畫法的嘗試並不一致，或者不太正確。

In 15th century Florence, artists realized the illusion of perspective could be achieved with higher degrees of sophistication by applying mathematical principles.

在15世紀佛羅倫斯，藝術家已知悉運用數學原理得以實現更高精細度的透視錯覺。

In 1485, Leonardo da Vinci manipulated the mathematics to create the first known anamorphic drawing.

1485年，達文西運用數學創建出第一個已知的變形圖畫法。

A number of other artists later picked up the technique, including Hans Holbein in "The Ambassadors."

其他藝術家後來承襲這個技巧，包括漢斯·霍爾班在他的畫作「大使」。

This painting features a distorted shape that forms into a skull as the viewer approaches from the side.

這幅畫畫面中扭曲的形狀，當觀眾從側面接近時就會形成顱骨。

In order to understand how artists achieve that effect, we first have to understand how perspective drawings work in general.

要了解藝術家如何達成這樣的效果，我們首先要了解透視圖一般畫法。

Imagine looking out a window.

想像一下你從窗口望出去

Light bounces off objects and into your eye, intersecting the window along the way.

光線自物體反彈回來，進入你的眼睛，沿著路線與窗戶相交。

Now, imagine you could paint the image you see directly onto the window while standing still and keeping only one eye open.

現在，想像一下你可以將你看到的圖像直接繪製到窗口上，你人是站直的，且只睜開一隻眼。

The result would be nearly indistinguishable from the actual view with your brain adding depth to the 2-D picture, but only from that one spot.

結果幾乎與實際所視無法區別，因為你的大腦會幫2-D照片加上深度，但只從你看到的那一點。

Standing even just a bit off to the side would make the drawing lose its 3-D effect.

即便只是稍往旁邊站一點點，就會讓那幅畫失去3D效果。

Artists understand that a perspective drawing is just a projection onto a 2-D plane.

藝術家理解透視圖，只是投影到2-D平面上。

This allows them to use math to come up with basic rules of perspective that allow them to draw without a window.

這讓他們能使用數學來提出基本的透視規則，也允許他們無窗繪圖。

One is that parallel lines, like these, can only be drawn as parallel if they're parallel to the plane of the canvas.

其中之一使用平行線，像這樣，如果它們平行於畫布的平面，就只能把它畫成平行。

Otherwise, they need to be drawn converging to a common point known as the vanishing point.

否則，需要將它們匯集到一個共同點，稱為消失點。

So that's a standard perspective drawing.

這也是一個標準的透視圖。

With an anamorphic drawing, like "The Ambassadors," directly facing the canvas makes the image look stretched and distorted, but put your eye in exactly the right spot way off to the side, and the skull materializes.

拿變形圖畫來說，像「大使」，直接面對畫布，讓整個圖像看起來伸展和扭曲，一旦把你的眼睛放在旁邊正確的位置上，頭骨便馬上成形。

Going back to the window analogy, it's as if the artist painted onto a window positioned at an angle instead of straight on, though that's not how Renaissance artists actually created anamorphic drawings.

再類比回到窗口的例子，它就好像藝術家對準一個角度畫在一個窗口上，而不是直接畫上去，雖然這不是文藝復興時期藝術家所創造的變形圖。

Typically, they draw a normal image onto one surface, then use a light, a grid, or even strings to project it onto a canvas at an angle.

通常，他們會在一個表面上繪製正常圖像，然後使用燈光、格線、或甚至將細繩以一個特定角度投影到畫布上。

Now let's say you want to make an anamorphic sidewalk drawing.

現在假設你想在人行道上做一個變形圖

In this case, you want to create the illusion that a 3-D image has been added seamlessly into an existing scene.

在這種情況下，你想創造幻覺，要將3-D圖像無縫地加到現有的接縫中。

You can first put a window in front of the sidewalk and draw what you want to add onto the window.

你可以先在人行道前面放一個窗口，然後畫出你想要加到窗口上的東西。

It should be in the same perspective as the rest of the scene, which might require the use of those basic rules of perspective.

它應與接縫的剩餘部分具有相同的視角，而它可能需要到使用這些透視的基本規則。

Once the drawing's complete, you can use a projector placed where your eye was to project your drawing down onto the sidewalk, then chalk over it.

一旦完成繪圖，你就可以將投影機，放置在你眼睛的位置，將你的畫值投射到人行道上，然後用粉筆畫上去。

The sidewalk drawing and the drawing on the window will be nearly indistinguishable from that point of view, so viewers' brains will again be tricked into believing that the drawing on the ground is three-dimensional.

人行道上的繪圖和窗口上的繪圖，從這一視角幾乎無法區分，因此觀眾的大腦會再次受到愚弄而相信地面上的繪圖是三維的。

And you don't have to project onto a flat surface to create this illusion.

你甚至不必投射到平坦的表面上來創造這種錯覺

You can project onto multiple surfaces, or assemble a jumble of objects, that from the right point of view, appears to be something else entirely.

你可以投影到多面體上，或者組裝一堆混亂的物體，然後從正確的角度來看呈現出完全是別的東西。

All over the planet, you can find solid surfaces giving way to strange, wonderful, or terrifying visions.

在世界各處，你可以找到堅實表面轉化成許多奇特、美妙或恐怖的幻景。

From your sidewalk to your computer screen, these are just some of the ways that math and perspective can open up whole new worlds.

從你的人行道到電腦螢幕，而這只是其中一些透過數學和透視法打開新世界的大門的方法而已。