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題 名 | 150秒角隨機點立體圖之製作=150 Sec-Arc Random-Dot Stereogram Made with IBM Personal Computer |
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作 者 | 王藹侯; 林隆光; | 書刊名 | 中華民國眼科醫學會雜誌 |
卷 期 | 37:3 1998.09[民87.09] |
頁 次 | 頁247-255 |
分類號 | 416.7051 |
關鍵詞 | 隨機點立體圖; 迴旋積分; Stereopsis; Random-dot stereogram; RDS; Resolution; Convolution; |
語 文 | 中文(Chinese) |
中文摘要 | 以IBM個人電腦320×200像點的圖形模式製作的300秒角的隨機點立體圖NTU 已成功地推廣作為全國學齡前幼兒視覺篩檢之用。我們曾經以640×350像點的圖形模式製 作150秒角的隨機點立體圖,期望能更嚴格地篩出輕微的雙眼視異常。經試用,發現其偽陽 性率太高。我們認為是因為像點太細,小兒的視力無法解析出每一個像點及隨機點圖的花紋 質地,以致無法融像,也無法產生立體視。為了解決此一問題,我們用電腦圖學上的迴旋積 分(Convolution),去除隨機點圖的高空間頻率成分,留下低空間頻率成分,卻不影響立體圖 的像差,製作了適合臨床篩檢使用的150秒角隨機點立體圖。我們選擇作3次迴旋積分的圖 形,因其花紋質地的粗細較接近NTU300秒角隨機點立體圖。依照數學計算,不管像點大 小,隨機點圖包含了所有的空間頻率,並且每一頻率的比重是相同的。事實上並非如此,比 較320和640像點的隨機點立體圖,可以發現後者低頻的成分較少,整張圖看似一片均勻的 灰色而少有可用以雙眼融像的花紋。可能的原因有二:(1)像點是數位化而非連續性的;(2) 亮度只有黑、白兩種,也是數位化而非連續的,因此套用傅立葉分析,會產生偏差。 |
英文摘要 | The random-dot stereogram NTU of 300 secarc disparity, which is created with 320 x 200 pixel graphic mode of IBM personal computer, has been extensively used as nationwide visual screening for preschool children. We had tried to create 150 secarc stereograms, with finer pixel of 640 x 350 pixel graphic mode, for screening of even subtle binocular abnormalities. It failed due to high over-referral rate. We supposed the reason was that over-small pixel, and thus over-fine random dot texture, went beyond the resolving ability of immature visual system of young children. They could not fuse, and thus could not get the stereopsis. To slove this problem, we applied CONVOLUTION, a method of digital image processing, to remove high spatial frequency components yet preserve low spatial frequency componets of random dot image. The disparity did not change with convolution and we thus successfully created 150 sec-arc random-dot stereograms suitable for screening of preschool children. The stereograms were processed by convolving 3 times to match the texture of 300 sec-are NTU stereograms. According to mathematics, the random dot image comprises of all spatial frequencies in equal weight, i.e. white noise, despite of the pixel size. In fact it is not true. Comparing random dot stereograms of 320 vs. 640 pixels, it is clear the latter comprises fewer low spatial frequency components, its texture is finer and looks more homogeneous and is thus harder to fuse. This discordance against mathematics may come from (1) the computer graphic is composed of pixels which are digitized and non-continuous; (2) the random dot image has only two gray levels, white and black, this is also digitized and non-continuous. These non- continuities introduce errors on Fourier transformation. |
本系統中英文摘要資訊取自各篇刊載內容。