feat(文件拆分): 拆分字体图像基础能力

internal/base/image/format.go

@@ -0,0 +1,31 @@
+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package image
+
+// NormalizeFormat 标准化印章媒体类型
+// 入参: s 原始媒体类型
+// 返回: string 标准媒体类型
+func NormalizeFormat(s string) string {
+	switch s {
+	case "jpg":
+		return "jpeg"
+	case "bmp":
+		return "bmp"
+	case "jb2", "gbig2":
+		return "jbig2"
+	default:
+		return s
+	}
+}