[求助]高手指教!erdas裁剪后影像颜色变化，怎么回事啊,急~~

<span class="Apple-style-span" style="WORD-SPACING: 0px; FONT: 14px="14px" /25px tahoma, 'MS Shell="Shell"  Dlg', Arial, Helvetica, verd; TEXT-TRANSFORM: none; COLOR: rgb(50,52,86); TEXT-INDENT: 0px; WHITE-SPACE: normal; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(243,243,247); orphans: 2; widows: 2; webkit-text-decorations-in-effect: none; webkit-text-size-adjust: auto; webkit-text-stroke-width: 0px">8幅ETM影像镶嵌的图像，用aoi裁剪后颜色就跟以前不一样了，感觉像素质量也变差了，这是怎么回事啊？求高手指教！！！<img src="http://emuch.net/bbs/images/smilies/shuai.gif" align="absMiddle" border="0"/></span><br/><br/>