彩色操作过滤器海报

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     <feComponentTransfer>
       <feFuncR type="discrete" tableValues="0 0.25 0.75 1.0"/>
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       <feFuncB type="discrete" tableValues="0 0.25 0.75 1.0"/>
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   <image xlink:href="https://upload.wikimedia.org/wikipedia/commons/4/42/Andy_Warhol_1975.jpg" x="20px" y="20px" width="300px" height="600px" preserveAspectRatio="xMinYMin meet" />
   <image filter="url(#posterize)" xlink:href="https://upload.wikimedia.org/wikipedia/commons/4/42/Andy_Warhol_1975.jpg" x="340px" y="20px" width="300px" height="600px" preserveAspectRatio="xMinYMin meet"/>
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