Editing Ambiguous image (section)

==Perceiving the image in mid-level vision==
[[File:KB ambiguous image.png|thumb|Rare example of an ambiguous image that can be interpreted in more than two ways: as the letters "KB", the mathematical inequality "1 < 13" or the letters "VD" with their mirror image.<ref name="protein_ambig">{{Cite journal | last1=Postic| first1=Guillaume| last2=Ghouzam| first2=Yassine| last3=Chebrek| first3=Romain| last4=Gelly| first4=Jean-Christophe| date=2017| title=An ambiguity principle for assigning protein structural domains| journal=Science Advances| volume=3| issue=1| pages=e1600552| doi=10.1126/sciadv.1600552| issn=2375-2548| pmc=5235333| pmid=28097215| bibcode=2017SciA....3E0552P}}</ref>]]

When we see an image, the first thing we do is attempt to organize all the parts of the scene into different groups.<ref name="halko">{{cite thesis |last1=Halko |first1=Mark Anthony |year=2008 |title=Illusory contour and surface completion mechanisms in human visual cortex |id={{ProQuest|621754807}} }}</ref> To do this, one of the most basic methods used is finding the edges. Edges can include obvious perceptions such as the edge of a house, and can include other perceptions that the brain needs to process deeper, such as the edges of a person's facial features. When finding edges, the brain's visual system detects a point on the image with a sharp contrast of lighting. Being able to detect the location of the edge of an object aids in recognizing the object. In ambiguous images, detecting edges still seems natural to the person perceiving the image. However, the brain undergoes deeper processing to resolve the ambiguity. For example, consider an image that involves an opposite change in magnitude of luminance between the object and the background (e.g. From the top, the background shifts from black to white, and the object shifts from white to black). The opposing [[gradient]]s will eventually come to a point where there is an equal degree of luminance of the object and the background. At this point, there is no edge to be perceived. To counter this, the visual system connects the image as a whole rather than a set of edges, allowing one to see an object rather than edges and non-edges. Although there is no complete image to be seen, the brain is able to accomplish this because of its understanding of the physical world and real incidents of ambiguous lighting.<ref name="Wolfe"/>

In ambiguous images, an illusion is often produced from [[illusory contours]]. An illusory contour is a perceived contour without the presence of a physical gradient. In examples where a white shape appears to occlude black objects on a white background, the white shape appears to be brighter than the background, and the edges of this shape produce the illusory contours.<ref>{{cite journal | last1 = Bradley | first1 = D.R. | last2 = Dumais | first2 = S.T. | year = 1975 | title = Ambiguous cognitive contours | journal = Nature | volume = 257 | issue = 5527| pages = 582–584 | doi = 10.1038/257582a0 | pmid = 1165783 | bibcode = 1975Natur.257..582B | s2cid = 4295897 }}</ref> These illusory contours are processed by the brain in a similar way as real contours.<ref name="halko"/> The visual system accomplishes this by making inferences beyond the information that is presented in much the same way as the luminance gradient.