Che sia la compressione JPEG troppo alta? Modifica il parametro necessario per settare questo valore.
codice:
long nQuality = 100;
ImageCodecInfo[] icf = ImageCodecInfo.GetImageEncoders();
EncoderParameters encps = new EncoderParameters(2);
EncoderParameter ep1 = new EncoderParameter( System.Drawing.Imaging.Encoder.Quality, nQuality );
EncoderParameter ep2 = new EncoderParameter( System.Drawing.Imaging.Encoder.Compression, 90 );
encps.Param[0] = ep1;
encps.Param[1] = ep2;
thumbNailImg.Save ( Request.PhysicalApplicationPath + imageUrlThumb + MyString , icf[1], encps);
thumbNailImg.Dispose();