Question

We have a piece of code which saves a .Net System.Drawing.Bitmap to file. The Save call is specifying the file location as well as the ImageFormat which we are expecting to save the image data as a Jpeg so out code looks like this:

public MediaFile IngestImage(System.Drawing.Bitmap imgSrc, string name){
     ... // left out because it is not relevant to this question
     imgSrc.Save(fullPath, System.Drawing.Imaging.ImageFormat.Jpeg);
     ... // left out because it is not relevant to this question
}

For some reason every now and then this method generates PNG images as .jpg files. Most of the time it is not a big deal however another piece of the project has issues with these files not being actual jpegs (Windows Media Services).

Any help is appreciated, has anyone ever seen this?

Note:
full path is something like “\servcer\share\file.jpg”. We are saving jpg’s with the extension “jpg”. Hence the issue… Later we are creating publishing points on a Windows Media Server to play a SMIL playlist we then have to “Announce” the files and formats to the publishing point when the publishing point starts playing it expects a Jpg file because that is the extension of the file and the content is actually a PNG

Here is the actual code creating the BitpMap object that is passed into the above method…

        public static Bitmap CreateBitmap(string text, int height, int width, Color foregroundColor, Color backgroundColor, string fontName, int fontSize, bool antialias)
    {
        // Initialize graphics
        Bitmap bmp = new Bitmap(width, height, PixelFormat.Format24bppRgb);
        using (Graphics g = Graphics.FromImage(bmp))
        {
            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            //g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
            if (antialias)
            {
                g.SmoothingMode = SmoothingMode.AntiAlias;
                g.TextRenderingHint = TextRenderingHint.AntiAlias;
            }

            // Set colors
            SolidBrush fgBrush = new SolidBrush(foregroundColor);
            SolidBrush bgBrush = new SolidBrush(backgroundColor);

            // paint background
            RectangleF rectF = new RectangleF(0, 0, width, height);
            g.FillRectangle(bgBrush, rectF);

            // Load font
            FontFamily fontFamily = FontFamily.GenericSerif;
            Font font = new Font(fontFamily, fontSize, FontStyle.Regular, GraphicsUnit.Pixel);
            try
            {
                fontFamily = new FontFamily(fontName);
                font = new Font(fontFamily, fontSize, FontStyle.Regular, GraphicsUnit.Pixel);
            }
            catch { }

            // Set font direction & alignment
            StringFormat format = new StringFormat();
            format.Alignment = StringAlignment.Center;
            format.LineAlignment = StringAlignment.Center;

            // Finally, draw the text
            g.DrawString(text, font, fgBrush, rectF, format);

            return bmp;
        }
    }

Answer 1

I’d approach this by:

1. paring down CreateBitmap(). For instance, does the problem appear if you remove everything except line that calls new and the return line? I’d assume it would, but it’s worth checking. If on the odd chance the problem disappears with this modification, then use a binary search to see if you can track it down to a particular line.

2. wrapping the Save call with try/catch to see if somewhere a ExternalException is being silently eaten. Bitmap.Save() (inherited from Image.Save()) says the following about ExternalException:

The image was saved with the wrong
image format.

-or-

The image was saved to the same file
it was created from.

Is is possible that the files that fail already exist at fullPath in PNG format with the .jpg extension?