Correct direction (size) of image thumbnail

Question

Hello.

I am doing a little image viewer. I have a listView controll, and put there an  image thumbnails. To get the thumbnails from images, i have this code:

        Image thumbnail(System.String pathToFile)
        {
                Image.GetThumbnailImageAbort myCallback = new Image.GetThumbnailImageAbort(ThumbnailCallback);
                Bitmap myBitmap = new Bitmap(pathToFile);
                Image myThumbnail = myBitmap.GetThumbnailImage(120, 90, myCallback, IntPtr.Zero);
                return myThumbnail;
        }

        /////////////////////////////////////
        
        public bool ThumbnailCallback()
        {
            return false;
        }

Image thumbnails are placed in listView as large icons with resolution 120 x 90 pix.

All is OK, if the image is horizontal, but when it is vertical, the thumbnail is stretched. What I have to do to fix this? And is there any reason to write down any text on thumbnails like this (like information about resolution, or filesize)?

Answer 1

This is because the height and width must be multiplied by an identical factor to maintain the proportion width / height.  I think the following code will do what you want given allowEnlarge = false and pad = true (but feel free to experiment with other parameters).

        /// <summary>
        /// Generates a thumbnail that fits in specified bounds while maintaining the proportions
        /// of the original image.
        /// </summary>
        /// <param name="fileName">The path and filename of the original image.</param>
        /// <param name="bounds">The maximum width and height for the returned image.</param>
        /// <param name="allowEnlarge">If true, the original image may be enlarged or reduced.
        ///   If false, the original image may only be reduced.</param>
        /// <param name="pad">If true, the thumbnail is centered in an image that has exactly
        ///   the specified bounds. If false, the returned image has equal or lesser bounds than
        ///   those specified.</param>
        /// <returns>The thumbnail image.</returns>
        private static Image GenerateThumbnail(string fileName, Size bounds, bool allowEnlarge, bool pad)
        {
            using (Bitmap bmp = new Bitmap(fileName))
            {
                Size targetSize;

                double hFit = (double) bounds.Height / bmp.Height;
                double wFit = (double) bounds.Width / bmp.Width;

                double factor = Math.Min(hFit, wFit);
                if (!allowEnlarge)
                {
                    factor = Math.Min(factor, 1.0);
                }

                targetSize = new Size((int)(bmp.Width * factor), (int)(bmp.Height * factor));

                if (pad)
                {
                    using (Image thumbnail = bmp.GetThumbnailImage(targetSize.Width, targetSize.Height, null, IntPtr.Zero))
                    {
                        Bitmap centeredBitmap = new Bitmap(bounds.Width, bounds.Height);
                        using (Graphics g = Graphics.FromImage(centeredBitmap))
                        {
                            g.DrawImage(thumbnail,
                                (centeredBitmap.Width - thumbnail.Width) / 2, (centeredBitmap.Height - thumbnail.Height) / 2,
                                thumbnail.Width, thumbnail.Height);
                        }
                        return centeredBitmap;
                    }
                }
                else
                {
                    return bmp.GetThumbnailImage(targetSize.Width, targetSize.Height, null, IntPtr.Zero);
                }
            }
        }

> And is there any reason to write down any text on thumbnails like this (like information about resolution, or filesize)?

Not sure what you mean.  I suppose this would depend on your application.

Answer 2

Woow...

This is EXACTLY, what I need :)

The class Graphics is, what I was searching for. My second question was - how can I write info about original image on the thumbnail (resolution etc). Now I can write everything using Graphics.DrawString method :)

Thank You Very Much for helping :)