In many web applications such as online photo albums, there is a need to convert all
images to fixed-size (usually square) thumbnails.
To preserve the aspect ratio and orientation of the original image in a
square thumbnail, landscape-oriented images need to have margins added
on the top and bottom, and portrait-oriented images on the left and right.
AspJpeg can add margins to thumbnails by means of "negative cropping", i.e. using the Crop method
with some or all of the coordinates being outside the coordinate space of the thumbnail.
Negative cropping is described here.
The color of the margin areas is black by default and can be changed via the
property objJpeg.Canvas.Brush.Color.
The following code snippet creates a square 200x200 thumbnail of an arbitrary image
with white margins. The thumbnail dimensions are specified via
the variables DesiredWidth and DesiredHeight. In this particular example,
these are set to the same number (200 pixels) but they can be arbitrary numbers not
necessarily equal to each other.
VB Script:
Set Jpeg = Server.CreateObject("Persits.Jpeg")
Jpeg.Open "c:\path\image.jpg"
Jpeg.PreserveAspectRatio = True
DesiredWidth = 200
DesiredHeight = 200
If Jpeg.OriginalWidth / DesiredWidth > Jpeg.OriginalHeight / DesiredHeight Then
Jpeg.Width = DesiredWidth
dy = Int((DesiredHeight - Jpeg.Height) / 2)
dy1 = DesiredHeight - Jpeg.Height - dy
dx = 0
dx1 = 0
Else
Jpeg.Height = DesiredHeight
dx = Int((DesiredWidth - Jpeg.Width) / 2)
dx1 = DesiredWidth - Jpeg.Width - dx
dy = 0
dy1 = 0
End If
' Apply negative cropping with white background
Jpeg.Canvas.Brush.Color = &HFFFFFF
Jpeg.Crop -dx, -dy, Jpeg.Width + dx1, Jpeg.Height + dy1
Jpeg.SaveUnique "c:\path\out.jpg"
C#:
IASPJpeg objJpeg = new ASPJpeg();
objJpeg.Open( @"c:\path\image.jpg" );
objJpeg.PreserveAspectRatio = 1;
int DesiredWidth = 200;
int DesiredHeight = 200;
int dx, dy, dx1, dy1;
if( objJpeg.OriginalWidth / DesiredWidth > objJpeg.OriginalHeight / DesiredHeight )
{
objJpeg.Width = DesiredWidth;
dy = (DesiredHeight - objJpeg.Height) / 2;
dy1 = DesiredHeight - objJpeg.Height - dy;
dx = 0;
dx1 = 0;
}
else
{
objJpeg.Height = DesiredHeight;
dx = (DesiredWidth - objJpeg.Width) / 2;
dx1 = DesiredWidth - objJpeg.Width - dx;
dy = 0;
dy1 = 0;
}
// Apply negative cropping with white background
objJpeg.Canvas.Brush.Color = 0xFF0000;
objJpeg.Crop( -dx, -dy, objJpeg.Width + dx1, objJpeg.Height + dy1 );
objJpeg.SaveUnique( @"c:\path\out.jpg" );
The margins can also be made fully transparent by using PNG
as the output format and adding an alpha channel to the image.
The following lines of code should be added after the call to the Crop method
if you want your thumbnails to have transparent margins:
VB Script:
...
Set Alpha = Server.CreateObject("Persits.Jpeg")
Alpha.New DesiredWidth, DesiredHeight, 0 ' fully transparent
Alpha.Canvas.Brush.Color = &HFFFFFF ' fully opaque
Alpha.Canvas.Pen.Color = &HFFFFFF ' fully opaque
Alpha.Canvas.DrawBar dx, dy, Jpeg.Width - dx1, Jpeg.Height - dy1
Alpha.ToGrayscale(0)
Jpeg.SetAlpha Alpha, False
Jpeg.PNGOutput = true
Jpeg.SaveUnique "c:path\out.png"
C#:
...
IASPJpeg objAlpha = new ASPJpeg();
objAlpha.New( DesiredWidth, DesiredHeight, 0 ); // fully transparent
objAlpha.Canvas.Brush.Color = 0xFFFFFF; // fully opaque
objAlpha.Canvas.Pen.Color = 0xFFFFFF; // fully opaque
objAlpha.Canvas.DrawBar( dx, dy, objJpeg.Width - dx1, objJpeg.Height - dy1 );
objAlpha.ToGrayscale(0);
objJpeg.SetAlpha( (ASPJpeg)objAlpha, false );
objJpeg.PNGOutput = 1;
objJpeg.SaveUnique( @"c:\path\out.png" );
The PNG format and alpha channel are described here.
