Exif thumbnail data

Question

Hi,

I'm currently a bit stucked in exif. I extract the thumbnail from the JPEG using GDI+ with C#. I wanted to get it unscaled so I used 0 as parameters to ImageWidth and ImageHeight parameters in the GetThumbnailImage function of the Image class. I always get an image size of 160x120 but I assume there can be different sizes and that GetThumbnailImage does not scale. I see that there could be additional exif data in the thumbnail, but I search for a fast way to decide whether ti scale the thumbnail or the primary image.

Is there any info about the thumbnail size in the primary images exif data? The tags I found until now doesn't seen to fit.

Has anyone done something similar?

Thanks in advance, Sascha