fpexif: Add introductory readme.txt; minor improvements in console_demo. New method TExifData.Save.

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@6084 8e941d3f-bd1b-0410-a28a-d453659cc2b4

components/fpexif/examples/console_demo/console_demo.pas

@@ -29,12 +29,16 @@ begin
         WriteLn(tag.AsString);
 
       // (2) shutter speed used when taking the photo
-      Write('Shutter speed: ':20);
       tag := imgInfo.ExifData.TagByName['ShutterSpeed'];
-      if tag = nil then
+      if tag <> nil then
-        WriteLn('--- not available in this file ---')
+        WriteLn('Shutter speed: ':20, tag.AsString)
       else
-        WriteLn(tag.AsString);
+      begin
+        // (3) Sometimes alternative tags are availabe
+        tag := imgInfo.ExifData.TagByName['ExposureTime'];
+        if tag <> nil then
+          WriteLn('Exposure time: ':20, tag.AsString);
+      end;
 
       // Add user comment
       imgInfo.ExifData.TagByName['UserComment'].AsString := 'This is my favorite photo.';
@@ -62,6 +66,7 @@ begin
     imgInfo.Free;
   end;
 
+  WriteLn;
   WriteLn('Press ENTER to quit...');
   ReadLn;
 

components/fpexif/fpemetadata.pas

@@ -78,6 +78,7 @@ type
     destructor Destroy; override;
     procedure LoadFromFile(const AFileName: String);
     procedure LoadFromStream(AStream: TStream);
+    procedure Save;
     procedure SaveToFile(const AFileName: String; AImgFile: String = '');
 
     function CreateExifData(ABigEndian: Boolean = false): TExifData;
@@ -562,6 +563,11 @@ begin
   end;
 end;
 
+procedure TImgInfo.Save;
+begin
+  SaveToFile(FFileName);
+end;
+
 procedure TImgInfo.SaveToFile(const AFileName: String; AImgFile: String = '');
 var
   ms: TMemoryStream;

components/fpexif/readme.txt

@@ -0,0 +1,110 @@
+================================================================================
+fpexif 
+================================================================================
+
+--------------------------------------------------------------------------------
+Overview
+--------------------------------------------------------------------------------
+fpexif is an fpc/Lazarus library for displaying and manipulating meta data in
+image files. 
+
+fpexif works without the LCL. 
+
+Meta data systems supported are
+- EXIF (including thumbnail, GPS, and manufacturer notes (partially) )
+- IPTC
+
+Image formats 
+- JPEG
+- TIFF
+
+The majority of meta data tags can be modified and written back to file. It 
+should be emphasized, however, that the EXIF maker notes are poorly documented
+and often become unreadable after editing an EXIF structure.
+
+Some examples in which fpexif can be applied:
+- add user comments, keywords and other documentation
+- fix date/time information (incorrect time/zone at camera when travelling 
+  in foreign countries)
+- adding GPS information to scanned photographs
+- remember exposure settings of difficult photos
+
+
+--------------------------------------------------------------------------------
+Quick introduction
+--------------------------------------------------------------------------------
+
+The basic class is TImgInfo (in unit fpeMetaData). It has properties to read
+meta data from file/stream (LoadFromFile, LoadFromStream) and to write them
+back (SaveToFile).
+
+EXIF data found in the file are stored by the object ExifData from which every
+tag can be acessed as TagByID[ATagID: TTagID] or TagByName[AName: String].  
+(TTagID is a DWord value containing the numerical ID of a tag in the low-word, 
+and the ID of the "directory" to which the tag belongs in the highword.)
+
+The properties TagByID and TagByName return a TTag instance in which the tag 
+value is stored. The type of the value depends on the type of the tag and can 
+be accessed by calling AsString, AsInteger, Asfloat, AsIntegerArray, 
+AsFloatArray etc. TTag is declared in unit fpeTags.
+
+
+--------------------------------------------------------------------------------
+Example
+--------------------------------------------------------------------------------
+Read meta data from a file, write a particular tag, modify a tag, write back.
+See also "console_demo".
+
+  uses
+    fpeMetadata, fpeTags;
+    
+  var
+    imgInfo: TImgInfo;
+    tag: TTag;
+  begin
+    imgInfo := TImgInfo.Create;
+    try
+      // Read file
+      imgInfo.LoadFromFile('MyImage.jpg');
+      
+      // Check for EXIF meta data
+      if imgInfo.HasEXIF then begin
+      
+        // Read the shutter speed used when taking an image from EXIF data
+        WriteLn(
+          'ShutterSpeed: ',
+	  imgInfo.ExifData.TagByName['ShutterSpeed'].AsString
+        );
+	
+	// or better (to avoid the exception if this particular tag does not exist):
+	tag := imgInfo.ExifData.TagByName['ShutterSpeed'];
+	if tag <> nil then WriteLn('ShutterSpeed: ', tag.AsString);
+      
+        // Add a user comment to the EXIF data
+        imgInfo.ExifData.TagByName['UserComment'].AsString := 'My best photo';
+      
+        // Save the modified meta data to file
+        imgInfo.SaveToFile('MyImage_edited.jpg');
+	// or: imgInfo.Save;  // overwrite currently loaded file
+    
+      end;
+    finally
+      imgInfo.Free;
+    end;
+  end;
+  
+
+--------------------------------------------------------------------------------
+Tested systems
+--------------------------------------------------------------------------------
+* Lazarus 1.0/fpc 2.6.0 up to Lazarus 1.9/fpc 3.0.4
+* Delphi 7.0
+* Delphi XE2
+* Delphi 10.2 Tokyo
+
+
+--------------------------------------------------------------------------------
+License
+--------------------------------------------------------------------------------
+Modified LGPL (like Lazarus)
+