如果把人的眼睛比作一部相機的話,那它有可能是性能最為強勁的一部(雖然參數不一定最強)。近日網上出現一篇文章則給出了更為具體的說法:
如果硬性比較,人眼大約等效於一台50毫米焦距,光圈F4-F32可變,400萬像素——是的,隻有400萬像素,感光度ISO50-ISO6400,快門1/24的不停連續拍攝的相機。 鏡頭約等於3片3組,全部由非球麵鏡組成,光圈(瞳孔)小於F32時,一般是某種化學藥品中毒,大於F2.8時~~~那是死人。對焦速度極高,在0.5秒內就能完成從最遠到最近的切換,永不跑焦。 非近視的情況下,景深極大。 影像處理器大約相當於4塊Digital 3,並行工作,而後台的模糊識別處理器,則無法用地球上的計算機來衡量。 色彩不好說,一般是認為在32位和48位之間。
但若細看文章,就會發現其中一些十分有趣且蹊蹺的地方。例如在上麵引用文字的前一段,就寫著“保守估計眼睛的水平可視角度是120度,垂直可視角度是60度,換算下來等於5.76億像素的圖像數據”;而在文章結尾,則寫著“即使僅以120度計算,像素就可達到5億7600萬像素”。
那麽,人眼的像素數到底是400萬,還是5.76億呢?要弄清這個問題,有必要對文章的數據來源做一番考證。經過簡單的網絡搜索發現,原來引文的數據來源共有3處:
引文前3段最早發表在2007年3月21日的《信息時報》上,新浪科技曾有過轉載。其中給出的數據是5.76億,依據在原文有說明。
2007年3月21日《信息時報》相關報道
本文引用段落,則來自一個個人博客(來源)。原作者給出400萬像素的理由是:“人眼大約擁有500萬個是神經細胞,其中大約有100萬是無法識別色彩的神經細胞,所以人眼的成像能力大約相當於400萬像素”。
看到這裏,其實真相已經明了。因為在《信息時報》的報道中開篇已經說明:“可以把人的眼睛想像成等同於500萬像素。但是,在眼睛裏麵還有一億個棒狀細胞……在你眼睛所示畫麵的銳利程度方麵扮演著重要的角色”。
在本文引用段落之後至結尾的文字,則摘自百度百科的“人眼”詞條。不難發現其內容與《信息時報》的報道是一致的,或者說是同一個理論的2種說法。而這個理論其實是德國人Konig在1897年在《Die Abhangigkeit der Sehscharfe von der Beleuchtungsintensitat》一書中提出的。
至此已經了然,也許是引文作者在“做”文章時的疏忽,總之人眼像素相當於400萬的結論恐怕不夠準確。人眼其實是一台像素高達5.76億的“超級相機”。
Your Eye's "megapixel" Resolution
The average human retina has five million cone receptors on it. Since the cones are responsible for colour vision, you might suppose that this equates to a five megapixel equivilant for the human eye.
But there are also a hundred million rods that detect monochrome contrast, which plays an important role in the sharpness of the image you see. And even this 105MP is an underestimate because the eye is not a still camera.
You have two eyes (no kidding!) and they continually flick around to cover a much larger area than your field of view and the composite image is assembled in the brain - not unlike stitching together a panoramic photo. In good light, you can distinguish two fine lines if they are seperate by at least 0.6 arc-minutes (0.01.Degrees).
This gives an equivilant pixel size of 0.3 arc-minutes. If you take a conservative 120 degrees as your horizontal field of view and 60 degrees in the vertical plane, this translates to ...
576 megapixels of available image data.
Curiously - as a counterpoint to this - most people cannot distinguish the difference in quality between a 300dpi and a 150dpi photo when printed at 6x4", when viewed at normal viewing distances.
So: although the human eye and brain when combined can resolve massive amounts of data, for imaging purposes, 150dpi output is more than enough to provide adequate data for us to accept the result as photographic quality.
But don't forget that women have more cones and men have more rods - I kid you not.Therefore the ladies see colours brighter than gents but can't see as well when it gets dark.