根据文件头来判断图片的类型

最新推荐文章于 2022-04-20 16:23:42 发布

雷布斯尼亚

最新推荐文章于 2022-04-20 16:23:42 发布

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文章标签： header function string

本文链接：https://blog.youkuaiyun.com/mu_x/article/details/7675232

本文介绍了一个用于识别图片文件类型的算法，包括GIF、JPEG、PNG、BMP等常见格式以及如何区分它们。

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unit UPictureCheck;

interface
type
  TPictureType=(ptGIF,ptJPEG,ptPNG,ptBMP,ptOther);
function CheckPictureType(fileName:string): TPictureType;
implementation
uses sysutils,classes;
var
  PngHeader: Array[0..7] of Char = (#137, #80, #78, #71, #13, #10, #26, #10);
  JPEGHeader:Array[0..1] of Char =(#255, #216);
  BMPHeader:Array[0..1] of Char = ('B','M');
  GIFHeader:Array[0..2] of Char =('G','I','F');
function CheckPictureType(fileName:string):TPictureType;
var
  fs:TFileStream;
  header:Array[0..7] of Char;
begin
  result:=ptOther;
  if not fileexists(fileName) then
    exit;
  fs:=TFileStream.Create(fileName,fmOpenRead);
  try
    fs.Read(Header[0], 8);
  finally
    fs.Free;
  end;
  if CompareMem(@header,@BMPHeader,2) then
  begin
    Result:=ptBMP;
    exit;
  end;
  if CompareMem(@header,@jpegheader,2) then
  begin
    Result:=ptJPEG;
    exit;
  end;
  if CompareMem(@header,@pngheader,8) then
  begin
    Result:=ptPNG;
    exit;
  end;
  if StrLIComp(@header,@GIFHeader,3)=0 then
  begin
    result:=ptGIF;
    exit;
  end;

end;
end.