Reading JPEG Thumbnails from EXIF
For next MBS Xojo Plugins we add new methods to JPEGImporterMBS class to read thumbnail from EXIF data in a JPEG file. This allows you to very quickly get a thumbnail image. We support ScaleFactor property for some years now, which allows you to read a JPEG scaled down and get only the pixel data decompressed you need. We use this often for a preview. The time differences may be for a test image here: 5.6 milliseconds for the thumbnail at 160x120, 64 milliseconds for a preview at 504x378 and 276 milliseconds for full image at 4032x3024 pixels. So in your projects, if you need to show JPEGs quickly, you may first check for a thumbnail, then for a scaled down preview and only if user double click the entry load the whole picture.
Here some sample code:
Dim file As FolderItem = SpecialFolder.Desktop.Child("test.jpg")
// first read header and check for thumbnail in EXIF
Dim j As New JPEGImporterMBS
j.file = file
j.ReadExifData = True
If j.ReadHeader Then
Dim thumbnailData As String = j.ExifThumbnail
If thumbnailData.LenB > 0 Then
thumbnailPic = picture.FromData(thumbnailData)
End If
// now read a scaled down image
Dim factor As Double = Min( j.Height / 300.0, j.Width / 300.0)
If factor >= 8.0 Then
j.ScaleFactor = 8
Elseif factor >= 4.0 Then
j.ScaleFactor = 4
Else
j.ScaleFactor = 2
End If
j.Import
Pic2 = j.Picture
// finally read full image
j.ScaleFactor = 0
j.Import
Pic3 = j.Picture
Else
MsgBox j.ErrorMessage
End If
Coming soon for MBS Plugins version 20.1pr5. See also CGImageSourceMBS class for MacOS to get quickly thumbnails for various image formats.