Hello,

Wanting to create a thumbnail of an image, i'm using the following piece of
code :

Public Sub Reduction(ByVal Source As String, ByVal Destination As String,
ByVal TailleX As String, ByVal TailleY As String, ByVal Resolution As
Integer, ByVal Fond As Boolean, ByVal ConserverRatio As Boolean, ByVal
PixelFormat As System.Drawing.Imaging.PixelFormat, ByVal ImageFormat As
System.Drawing.Imaging.ImageFormat, ByVal R As Integer, ByVal V As Integer,
ByVal B As Integer)
        'Declarations des variables recevant les dimensions proportionnelles
à l'original
        Dim Width_Out As Integer 'largeur proportionnelle original
        Dim Height_Out As Integer 'hauteur proportionnelle original
        'Declarations des variables recevant les dimensions de sortie
souhaitées
        Dim Final_X As Integer 'largeur de sortie
        Dim Final_Y As Integer 'hauteur de sortie
        'Déclaration du Bitmap d'entrée
        Dim Bitmap_In As Bitmap
        'Chargement de l'image source dans le bitmap d'entrée
        Bitmap_In = Image.FromFile(Source)
        'Conservation du Ratio (OUI/NON)
        If ConserverRatio Then
            'Calcul des dimensions de la miniature du bitmap d'entrée
            'si Largeur fixe
            If TailleY = "" And TailleX <> "" Then
                'Définition de la taille proprtionnelle
                Width_Out = CInt(TailleX)
                Height_Out = CInt(TailleX) * Bitmap_In.Height /
Bitmap_In.Width
                'Définition de la taille souhaitée
                Final_X = TailleX
                Final_Y = Height_Out
            Else
                'si Hauteur fixe
                If TailleX = "" And TailleY <> "" Then
                    'Définition de la taille proprtionnelle
                    Height_Out = CInt(TailleY)
                    Width_Out = CInt(TailleY) * Bitmap_In.Width /
Bitmap_In.Height
                    'Définition de la taille souhaitée
                    Final_X = Width_Out
                    Final_Y = TailleY
                Else
                    If Bitmap_In.Width >= Bitmap_In.Height Then
                        'Définition de la taille proprtionnelle
                        'si orientation = paysage
                        Width_Out = CInt(TailleX)
                        Height_Out = CInt(TailleX) * Bitmap_In.Height /
Bitmap_In.Width
                    Else
                        'Définition de la taille proprtionnelle
                        'si orientation = portrait
                        Height_Out = CInt(TailleY)
                        Width_Out = CInt(TailleY) * Bitmap_In.Width /
Bitmap_In.Height
                    End If
                    'Verification si la taille de la miniature est
compatible avec la taille souhaitée
                    'si Width_Out > TailleX
                    If Width_Out > TailleX Then
                        Width_Out = CInt(TailleX)
                        Height_Out = CInt(TailleX) * Bitmap_In.Height /
Bitmap_In.Width
                    End If
                    'si Height_Out > TailleY
                    If Height_Out > TailleY Then
                        Height_Out = CInt(TailleY)
                        Width_Out = CInt(TailleY) * Bitmap_In.Width /
Bitmap_In.Height
                    End If
                    'Définition de la taille souhaitée
                    Final_X = TailleX
                    Final_Y = TailleY
                End If
            End If
        Else
            'Définition de la taille proprtionnelle
            Width_Out = CInt(TailleX)
            Height_Out = CInt(TailleY)
            'Définition de la taille souhaitée
            Final_X = TailleX
            Final_Y = TailleY
        End If
        'Déclaration du Bitmap de sortie
        Dim Bitmap_Temp As New Bitmap(Width_Out, Height_Out, PixelFormat)
        'Déclaration de la surface de dessin du bitmap d'entrée
        Dim MyGraphics_Temp As Graphics = Graphics.FromImage(Bitmap_Temp)
        'Modification de la surface de dessin du bitmap d'entrée en
respectant les proptions
        MyGraphics_Temp.DrawImage(Bitmap_In, 0, 0, Width_Out, Height_Out)
        'Liberation de la mémoire des éléments concernat le Bitmap d'entrée
        Bitmap_In.Dispose()
        Bitmap_In = Nothing
        'Déclaration du Bitmap de sortie
        Dim Bitmap_Out As Bitmap
        'Création d'un fond à l'image (OUI/NON)
        If Fond Then
            'Instanciation du Bitmap de sortie
            Bitmap_Out = New Bitmap(CInt(Final_X), CInt(Final_Y), PixelFormat)
            'Déclaration de la surface de dessin du bitmap de sortie
            Dim MyGraphics_out As Graphics = Graphics.FromImage(Bitmap_Out)
            'Definition de la couleur d'arrière-plan
            Dim Couleur As Color = Color.FromArgb(255, R, V, B)
            Dim MyBackground As New SolidBrush(Couleur)
            'Calcul des décalages Haut et gauche pour centrer de l'image
            Dim Top As Integer = (Bitmap_Out.Height - Bitmap_Temp.Height) / 2
            Dim Left As Integer = (Bitmap_Out.Width - Bitmap_Temp.Width) / 2
            'Definition de la resolution (dpi)
            Bitmap_Out.SetResolution(Resolution, Resolution)
            'Remplissage de tout les pixels de la couleur du fond
            MyGraphics_Out.FillRectangle(MyBackground, 0, 0,
Bitmap_Out.Width, Bitmap_Out.Height)
            'Recopie du bitmap d'entrée en position centrée
            MyGraphics_Out.DrawImageUnscaled(Bitmap_Temp, Left, Top,
Bitmap_Temp.Width, Bitmap_Temp.Height)
            'Sauvegarde du bitmap de sortie
            Bitmap_Out.Save(Destination, ImageFormat.Jpeg)
            'Liberation de la mémoire
            MyGraphics_out.dispose()
            MyGraphics_out = Nothing
            Bitmap_Out.Dispose()
            Bitmap_Out = Nothing
        Else
            'Instanciation du Bitmap de sortie
            Bitmap_Out = New Bitmap(CInt(Width_Out), CInt(Height_Out),
PixelFormat)
            'Déclaration de la surface de dessin du bitmap de sortie
            Dim MyGraphics_out As Graphics = Graphics.FromImage(Bitmap_Out)
            'Recopie du bitmap d'entrée
            MyGraphics_Out.DrawImageUnscaled(Bitmap_Temp, 0, 0,
Bitmap_Temp.Width, Bitmap_Temp.Height)
            'Sauvegarde du bitmap de sortie
            Bitmap_Out.Save(Destination, ImageFormat.Jpeg)
            'Liberation de la mémoire
            MyGraphics_out.dispose()
            MyGraphics_out = Nothing
            Bitmap_Out.Dispose()
            Bitmap_Out = Nothing
        End If
        MyGraphics_Temp.Dispose()
        MyGraphics_Temp = Nothing
        Bitmap_Temp.Dispose()
        Bitmap_Temp = Nothing
    End Sub

and calling it with the following one :

Reduction(Src, Dest, 221, 142, 72, True, True, PixelFormat.Format24bppRgb,
ImageFormat.Jpeg, 255, 255, 255)

Meanwhile, the quality of the generated thumbnail is not as good as i could
expect. Could this piece of code be optimised, in order to improve the
rendering quality.

Thanks

Resizing an image with a certain interpolation mode
<URL:http://dotnet.mvps.org/dotnet/faqs/?id=interpolationmode&lang=en>

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