Thumbnail quality question


#1

I am using the GetThumbnail method of the slide object to get an image for use in HTML and PDF.
Though I’m very happy with the product so far, there is a slight problem with the image quality of this method.
First of all it does not resemble the quality of neither a printout or a screenshow.
You can see som pixelation on fonts and images that doesen’t show up on printouts and screenshows.
I would suspect this is a problem with powerpoint itself, but it would be great if it could be solved. For now I have to scale the image to 0.99 to get some interpolation, but this is not optimal.

Another issue with the getthumbnail method is, I think it uses jpeg compression.
I would rather have an uncompressed thumbnail because compression jitters the outline of fonts.

With regards
Morten


#2

Dear Morten,

Most of the fonts problems will be solved soon.
The bad quality of images is not because of jpeg compression. It’s because of using System.Drawing.Image.GetThumbnail. I don’t know what algorithm MS used but results are awful. Probably we will use another method to scale it.


#3

One thing I know is that GetThumbnail will use any existing thumbnail integrated in the image. Some image formats like jpeg and tiff and other formats has a possibility for an integrated thumbnail.
Here is what i do to scale an image, this will probably give more control of the quality.

Private Function CreateScaledImage(ByVal img As System.Drawing.Image, ByVal sz As System.Drawing.Size) As System.Drawing.Image

Dim bmpdest As New Bitmap(sz.Width, sz.Height)
Dim gfx As Graphics = Graphics.FromImage(CType(bmpdest, System.Drawing.Image))
'Could use antialias instead, but this is probably more correct
gfx.SmoothingMode = Drawing2D.SmoothingMode.HighQuality
gfx.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic
gfx.DrawImage(img, 0, 0, sz.Width, sz.Height)

Return CType(bmpdest, System.Drawing.Image)
End Function


/Morten