fix code

hutool-swing/src/main/java/cn/hutool/swing/img/BackgroundRemoval.java

@@ -299,7 +299,7 @@ public class BackgroundRemoval {
 			}
 		}
 
-		final Map<String, Integer> map = new HashMap<>(list.size());
+		final Map<String, Integer> map = new HashMap<>(list.size(), 1);
 		for (final String string : list) {
 			Integer integer = map.get(string);
 			if (integer == null) {
@@ -309,7 +309,7 @@ public class BackgroundRemoval {
 			}
 			map.put(string, integer);
 		}
-		String max = "";
+		String max = StrUtil.EMPTY;
 		long num = 0;
 		for (final Map.Entry<String, Integer> entry : map.entrySet()) {
 			final String key = entry.getKey();
@@ -326,7 +326,7 @@ public class BackgroundRemoval {
 			return ImgUtil.toHex(Integer.parseInt(strings[0]), Integer.parseInt(strings[1]),
 					Integer.parseInt(strings[2]));
 		}
-		return "";
+		return StrUtil.EMPTY;
 	}
 
 	// -------------------------------------------------------------------------- private

hutool-swing/src/main/java/cn/hutool/swing/img/ImgUtil.java

@@ -1356,6 +1356,19 @@ public class ImgUtil {
 		return out.toByteArray();
 	}
 
+	/**
+	 * 根据文字创建透明背景的PNG图片
+	 *
+	 * @param str             文字
+	 * @param font            字体{@link Font}
+	 * @param fontColor       字体颜色，默认黑色
+	 * @param out             图片输出地
+	 * @throws IORuntimeException IO异常
+	 */
+	public static void createTransparentImage(String str, Font font, Color fontColor, ImageOutputStream out) throws IORuntimeException {
+		writePng(createImage(str, font, null, fontColor, BufferedImage.TYPE_INT_ARGB), out);
+	}
+
 	/**
 	 * 根据文字创建PNG图片
 	 *

hutool-swing/src/test/java/cn/hutool/swing/img/ImgUtilTest.java

@@ -1,7 +1,7 @@
 package cn.hutool.swing.img;
 
 import cn.hutool.core.io.FileUtil;
-import cn.hutool.swing.img.ImgUtil;
+import cn.hutool.core.io.IORuntimeException;
 import org.junit.Assert;
 import org.junit.Ignore;
 import org.junit.Test;
@@ -147,4 +147,26 @@ public class ImgUtilTest {
 		System.out.println(mainColor);
 	}
 
+	@Test
+	@Ignore
+	public void createImageTest() throws IORuntimeException, IOException {
+		ImgUtil.createImage(
+				"版权所有",
+				new Font("黑体", Font.BOLD, 50),
+				Color.WHITE,
+				Color.BLACK,
+				ImageIO.createImageOutputStream(new File("d:/test/createImageTest.png"))
+		);
+	}
+
+	@Test
+	@Ignore
+	public void createTransparentImageTest() throws IORuntimeException, IOException {
+		ImgUtil.createTransparentImage(
+				"版权所有",
+				new Font("黑体", Font.BOLD, 50),
+				Color.BLACK,
+				ImageIO.createImageOutputStream(new File("d:/test/createTransparentImageTest.png"))
+		);
+	}
 }