An image processing method for marking plaque fluorescent reaction area is provided, including the following steps: emitting natural light to an mouth region of a user； obtaining a first RGB image corresponding to the mouth region； emitting blue light to the mouth region； obtaining a second RGB image corresponding to the mouth region； respectively converting the first RGB image and the second RGB image into a first HSV image and a second HSV image； obtaining a first average brightness value corresponding to the first HSV image and a second average brightness value corresponding to the second HSV image； normalizing the first average brightness value or the second average brightness value according the first average brightness value and the second average brightness value to obtain a normalized image； converting the normalized image into a third RGB image, and obtaining a plurality of pixel points corresponding to the dental plaque according to the third RGB image and the first RGB image or the second RGB image； and marking the pixel points in the third RGB image.一種用以標示牙菌斑螢光反應區域之影像處理方法，包括：對一使用者之一口腔區域發出自然光；取得對應於口腔區域之一第一RGB影像；對口腔區域發出藍光；取得對應於口腔區域之一第二RGB影像；分別將第一RGB影像以及第二RGB影像轉換為一第一HSV影像以及一第二HSV影像；取得對應於第一HSV影像之一第一平均明度值以及對應於第二HSV影像之一第二平均明度值；根據第一平均明度值以及第二平均明度值之一者對第一平均明度值以及第二平均明度值之另一者作正規化以取得一經正規化之影像；將經正規化之影像轉換為一第三RGB影像，並根據第三RGB影像以及第一RGB影像或者第二RGB影像取得複數對應於牙菌斑之像素點；以及將上述像素點標示於第三RGB影像中。
