本文主要是介绍带Alpha通道的TIFF文件在GeoServer发布PNG瓦片失败的问题，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
我在使用GeoServer发布Tiff切PNG瓦片切不了，但是JPG可以，用QGIS转坐标系之后可以，但是用ArcGIS转坐标系之后不可以，看GeoServer日志发现报错如下：
org.geowebcache.GeoWebCacheException: Problem communicating with GeoServerat org.geoserver.gwc.layer.GeoServerTileLayer.getMetatilingReponse(GeoServerTileLayer.java:621)at org.geoserver.gwc.layer.GeoServerTileLayer.getTile(GeoServerTileLayer.java:558)at org.geowebcache.util.ResponseUtils.writeTile(ResponseUtils.java:101)at org.geowebcache.GeoWebCacheDispatcher.handleServiceRequest(GeoWebCacheDispatcher.java:426)at org.geowebcache.GeoWebCacheDispatcher.handleRequestInternal(GeoWebCacheDispatcher.java:286)at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:177)at org.geoserver.gwc.dispatch.GwcServiceProxy.dispatch(GwcServiceProxy.java:87)at jdk.internal.reflect.GeneratedMethodAccessor231.invoke(Unknown Source)at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.base/java.lang.reflect.Method.invoke(Method.java:566)at org.geoserver.ows.Dispatcher.execute(Dispatcher.java:867)at org.geoserver.ows.Dispatcher.handleRequestInternal(Dispatcher.java:268)at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:177)at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:51)at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1072)at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965)at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)at javax.servlet.http.HttpServlet.service(HttpServlet.java:529)at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)at javax.servlet.http.HttpServlet.service(HttpServlet.java:623)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:209)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.geoserver.filters.ThreadLocalsCleanupFilter.doFilter(ThreadLocalsCleanupFilter.java:28)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.geoserver.filters.SpringDelegatingFilter$Chain.doFilter(SpringDelegatingFilter.java:73)at org.geoserver.ows.HTTPHeadersCollector.doFilter(HTTPHeadersCollector.java:48)at org.geoserver.filters.SpringDelegatingFilter$Chain.doFilter(SpringDelegatingFilter.java:70)at org.geoserver.filters.HTTPMethodFilter.doFilter(HTTPMethodFilter.java:36)at org.geoserver.filters.SpringDelegatingFilter$Chain.doFilter(SpringDelegatingFilter.java:70)at org.geoserver.filters.LoggingFilter.doFilter(LoggingFilter.java:194)at org.geoserver.filters.SpringDelegatingFilter$Chain.doFilter(SpringDelegatingFilter.java:70)at org.geoserver.filters.SpringDelegatingFilter.doFilter(SpringDelegatingFilter.java:43)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.geoserver.platform.AdvancedDispatchFilter.doFilter(AdvancedDispatchFilter.java:39)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:337)at org.geoserver.security.filter.GeoServerCompositeFilter$NestedFilterChain.doFilter(GeoServerCompositeFilter.java:71)at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:115)at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:81)at org.geoserver.security.filter.GeoServerCompositeFilter$NestedFilterChain.doFilter(GeoServerCompositeFilter.java:75)at org.geoserver.security.filter.GeoServerCompositeFilter.doFilter(GeoServerCompositeFilter.java:92)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346)at org.geoserver.security.filter.GeoServerCompositeFilter$NestedFilterChain.doFilter(GeoServerCompositeFilter.java:71)at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:122)at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:116)at org.geoserver.security.filter.GeoServerCompositeFilter$NestedFilterChain.doFilter(GeoServerCompositeFilter.java:75)at org.geoserver.security.filter.GeoServerCompositeFilter.doFilter(GeoServerCompositeFilter.java:92)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346)at org.geoserver.security.filter.GeoServerAnonymousAuthenticationFilter.doFilter(GeoServerAnonymousAuthenticationFilter.java:53)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346)at org.geoserver.security.filter.GeoServerCompositeFilter$NestedFilterChain.doFilter(GeoServerCompositeFilter.java:71)at org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilterInternal(BasicAuthenticationFilter.java:166)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.geoserver.security.filter.GeoServerCompositeFilter$NestedFilterChain.doFilter(GeoServerCompositeFilter.java:75)at org.geoserver.security.filter.GeoServerCompositeFilter.doFilter(GeoServerCompositeFilter.java:92)at org.geoserver.security.filter.GeoServerBasicAuthenticationFilter.doFilter(GeoServerBasicAuthenticationFilter.java:81)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346)at org.geoserver.security.filter.GeoServerCompositeFilter$NestedFilterChain.doFilter(GeoServerCompositeFilter.java:71)at org.geoserver.security.filter.GeoServerSecurityContextPersistenceFilter$1.doFilterInternal(GeoServerSecurityContextPersistenceFilter.java:72)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.geoserver.security.filter.GeoServerCompositeFilter$NestedFilterChain.doFilter(GeoServerCompositeFilter.java:75)at org.geoserver.security.filter.GeoServerCompositeFilter.doFilter(GeoServerCompositeFilter.java:92)at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346)at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:221)at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:186)at org.geoserver.security.GeoServerSecurityFilterChainProxy.doFilter(GeoServerSecurityFilterChainProxy.java:142)at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:354)at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:267)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.geoserver.filters.XFrameOptionsFilter.doFilter(XFrameOptionsFilter.java:77)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.geoserver.filters.GZIPFilter.doFilter(GZIPFilter.java:48)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.geoserver.filters.SessionDebugFilter.doFilter(SessionDebugFilter.java:49)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.geoserver.filters.FlushSafeFilter.doFilter(FlushSafeFilter.java:42)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153)at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:481)at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:130)at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:673)at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:390)at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:926)at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1791)at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: org.geoserver.platform.ServiceException: Failed to encode the PNGat org.geoserver.wms.map.png.PNGJWriter.writePNG(PNGJWriter.java:49)at org.geoserver.wms.map.PNGMapResponse.formatImageOutputStream(PNGMapResponse.java:101)at org.geoserver.gwc.layer.GeoServerMetaTile.writeTileToStream(GeoServerMetaTile.java:131)at org.geowebcache.layer.TileLayer.saveTiles(TileLayer.java:523)at org.geoserver.gwc.layer.GeoServerTileLayer.getMetatilingReponse(GeoServerTileLayer.java:618)... 109 more
Caused by: java.lang.IllegalArgumentException: Could not find a scanline extractor for BufferedImage@3cdaf33f: type = 0 ColorModel: #pixelBits = 40 numComponents = 5 color space = com.sun.media.imageioimpl.common.BogusColorSpace@8e2d646 transparency = 1 has alpha = false isAlphaPre = false ByteInterleavedRaster: width = 256 height = 256 #numDataElements 5 dataOff[0] = 4at it.geosolutions.imageio.plugins.png.PNGWriter.writePNG(PNGWriter.java:60)at it.geosolutions.imageio.plugins.png.PNGWriter.writePNG(PNGWriter.java:48)at org.geoserver.wms.map.png.PNGJWriter.writePNG(PNGJWriter.java:47)... 113 more
错误是显示png编码失败，找不到扫描线提取器。而且如果通过WMS服务直接获取PNG图片会是如下状态：
但从报错也看不出所以然，只能一点点对比QGIS转坐标系之后的文件和ArcGIS转坐标系之后文件的区别。最后发现，虽然两个文件用ArcGIS看都是四个波段，但是如果用Photoshop打开，不能发布png的文件中有Alpha通道，能发布的文件没有Alpha通道。
Alpha通道是计算机图形学中的术语，指的是特别的通道，意思是“非彩色”通道，主要是用来保存选区和编辑选区。理论上Alpha通道跟透明度没有直接关系，但是也可以用Alpha通道来存透明度。
于是我在Photoshop里将Tiff的Alpha通道删了，果然就能够正常发布了。
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