Сохранение и извлечение JPEG изображений (и не только)

Сохранение и извлечение JPEG изображений (и не только)

Поля типа Graphic предназначены для работы с типами данных Bitmap, Icon, Metafiles, как и компонент DBImage.

Чтобы сохранить JPEG изображение, поле Blob должно иметь подтип Graphic, тогда мы сможем использовать приведенный код.

uses jpeg;

procedure TForm1.Button1Click(Sender: TObject);
var Jpg: TJpegImage;
      Stream: TMemoryStream;
begin
Jpg := nil;
Stream := nil;
try
// Создажим JPEG image и загрузим в него изображение из файла
Jpg := TJpegImage.Create;
Jpg.LoadFromFile('test.jpg');
// Создадим поток и загрузим изображение в поток
Stream := TMemoryStream.Create;
Jpg.SaveToStream(Stream);
Stream.Position := 0;
Table1.Append;
// Получим данные из потока в наше поле Blob field
TBlobField(Table1.FieldByName('Graph')).LoadFromStream(Stream);
Table1.Post;
except
jpg.Free;
Stream.Free;
raise;
end;
jpg.Free;
Stream.Free;
end;

To display a JPEG image stored in a Blob field in a TImage control, we
can use a code like the following for example in an AfterScroll event:

procedure TForm1.Table1AfterScroll(DataSet: TDataSet);
var
Stream: TMemoryStream;
Jpg: TJpegImage;
begin
Jpg := nil;
Stream := nil;
try
// Create a stream and load the contents of the Blob field
Stream := TMemoryStream.Create;
TBlobField(Table1.FieldByName('Graph')).SaveToStream(Stream);
if Stream.Size > 0 then begin
// Create a JPEG image and load it from the stream
Jpg := TJpegImage.Create;
Stream.Position := 0;
Jpg.LoadFromStream(Stream);
// Assign the JEPG image to the Picture property of an Image
Image1.Picture.Assign(Jpg);
end else
Image1.Picture.Assign(nil);
except
Image1.Picture.Assign(nil);
end;
jpg.Free;
Stream.Free;
end;

If you want to be able to store different images types (bitmaps, icons,
metafiles and jpegs) in a field, we can add a byte at the beginning of
the stream to indicate the image kind, and then we have to read this
byte first to know how to load and display the image appropriately. We
designed a full example to show how to do it.

1) Place the following components on a form and set their properties:

Table1: TTable
TableName = 'GraphTest.DB'
FieldDefs =
Field1
Name = 'Graph'
DataType = ftBlob
Size = 1
StoreDefs = True
DataSource1: TDataSource
DataSet = Table1
DBNavigator1: TDBNavigator
DataSource = DataSource1
Align = alBottom
PopupMenu1: TPopupMenu
Items =
mnuLoad: TMenuItem
Caption = '&Load...'
mnuClear: TMenuItem
Caption = '&Clear'
Image1: TImage
PopupMenu = PopupMenu1
dlgOpenPicture: TOpenPictureDialog
Options = [ofReadOnly, ofHideReadOnly, ofPathMustExist,
ofFileMustExist, ofNoTestFileCreate, ofEnableSizing]

2) Add "jpeg" to the uses clause:
uses
..., jpeg;

3) Add the following type declaration to the unit:
type
TGraphType = (gtBitmap, gtIcon, gtMetafile, gtJpeg);

4) Generate the following events:
procedure TForm1.FormCreate(Sender: TObject);
begin
if Not FileExists('GraphTest.DB') then
Table1.CreateTable;
Table1.Open;
end;

procedure TForm1.mnuLoadClick(Sender: TObject);
var
Jpg: TJpegImage;
Stream: TMemoryStream;
FileExt: string;
GraphType: TGraphType;
begin
if dlgOpenPicture.Execute then begin
Jpg := nil;
Stream := nil;
try
Stream := TMemoryStream.Create;
FileExt := LowerCase(ExtractFileExt(dlgOpenPicture.FileName));
if (FileExt = '.bmp') or (FileExt = '.dib') then begin
GraphType := gtBitmap;
Stream.Write(GraphType, 1);
with Image1.Picture.Bitmap do begin
LoadFromFile(dlgOpenPicture.FileName);
Image1.Picture.Bitmap.SaveToStream(Stream);
end;
end else if (FileExt = '.ico') then begin
GraphType := gtIcon;
Stream.Write(GraphType, 1);
with Image1.Picture.Icon do begin
LoadFromFile(dlgOpenPicture.FileName);
Image1.Picture.Bitmap.SaveToStream(Stream);
end;
end else if (FileExt = '.emf') or (FileExt = '.wmf') then begin
GraphType := gtMetafile;
Stream.Write(GraphType, 1);
with Image1.Picture.Metafile do begin
LoadFromFile(dlgOpenPicture.FileName);
Image1.Picture.Bitmap.SaveToStream(Stream);
end;
end else if (FileExt = '.jpg') or (FileExt = '.jpeg')
or (FileExt = '.jpe') then begin
Jpg := TJpegImage.Create;
Jpg.LoadFromFile(dlgOpenPicture.FileName);
Image1.Picture.Assign(Jpg);
GraphType := gtJpeg;
Stream.Write(GraphType, 1);
Jpg.SaveToStream(Stream);
end;
if (Table1.State <> dsEdit) and (Table1.State <> dsInsert) then
Table1.Edit;
Stream.Position := 0;
TBlobField(Table1.FieldByName('Graph')).LoadFromStream(Stream);
except
jpg.Free;
Stream.Free;
raise;
end;
jpg.Free;
Stream.Free;
end;
end;

procedure TForm1.mnuClearClick(Sender: TObject);
begin
Image1.Picture.Assign(nil);
if (Table1.State <> dsEdit) and (Table1.State <> dsInsert) then
Table1.Edit;
Table1.FieldByName('Graph').Assign(nil);  // Clear the field
end;

procedure TForm1.Table1AfterScroll(DataSet: TDataSet);
var
Stream: TMemoryStream;
Jpg: TJpegImage;
GraphType: TGraphType;
begin
Jpg := nil;
Stream := nil;
try
Stream := TMemoryStream.Create;
TBlobField(Table1.FieldByName('Graph')).SaveToStream(Stream);
if Stream.Size > 0 then begin
Stream.Position := 0;
Stream.Read(GraphType, 1);
case GraphType of
gtBitmap:   Image1.Picture.Bitmap.LoadFromStream(Stream);
gtIcon:     Image1.Picture.Icon.LoadFromStream(Stream);
gtMetafile: Image1.Picture.Metafile.LoadFromStream(Stream);
gtJpeg:   begin
Jpg := TJpegImage.Create;
Jpg.LoadFromStream(Stream);
Image1.Picture.Assign(Jpg);
end else
Image1.Picture.Assign(nil);  // Clear the image
end;
end else
Image1.Picture.Assign(nil);
except
Image1.Picture.Assign(nil);
end;
jpg.Free;
Stream.Free;
end;

Эта запись была добавлена в Пятница, 23 мая, 2008 - 11:10 В разделы BLOB поля, Базы данных. Вы можете подписаться на получение новых комментариев RSS 2.0 feed. Both comments and pings are currently closed.