Image thumbnails

[tmeers]

I have done some reading on this and my thumb nail generation works great with a few exceptions, this is what I need help with.

My code:

        public static byte[] ResizeImageFile(byte[] imageFile, int targetSize)
        {
            using (System.Drawing.Image oldImage = System.Drawing.Image.FromStream(new MemoryStream(imageFile)))
            {
                Size newSize = CalculateDimensions(oldImage.Size, targetSize);
 
                using (Bitmap newImage = new Bitmap(newSize.Width, newSize.Height, PixelFormat.Format24bppRgb))
                {
                    using (Graphics canvas = Graphics.FromImage(newImage))
                    {
                        canvas.SmoothingMode = SmoothingMode.AntiAlias;
                        canvas.InterpolationMode = InterpolationMode.HighQualityBicubic;
                        canvas.PixelOffsetMode = PixelOffsetMode.HighQuality;
                        canvas.DrawImage(oldImage, new Rectangle(new Point(0, 0), newSize));
                        MemoryStream m = new MemoryStream();
                        newImage.Save(m, ImageFormat.Jpeg);
                        return m.GetBuffer();
                    }
                }
 
            }
        }
 
        private static Size CalculateDimensions(Size oldSize, int targetSize)
        {
            Size newSize = new Size();
            if (oldSize.Width > oldSize.Height)
            {
                newSize.Width = targetSize;
                newSize.Height = (int)(oldSize.Height * (float)targetSize / (float)oldSize.Width);
            }
            else
            {
                newSize.Width = (int)(oldSize.Width * (float)targetSize / (float)oldSize.Height);
                newSize.Height = targetSize;
            }
            return newSize;
        } 

I am passing the targetSize and imageFile byte stream from the front end and streaming out 4 different sizes to be saved into a database for later use. And agian all is working well for large images. But when it comes to protrait and and images smaller than those being thumbnailed it goes astray. I read the post on dontnetslackers.com and changed a little in the CalculateSize method. Heres what happens:

Case 1: Images smaller than the thumbnailed size (small 100px, medium 250px, large 500px, and xlarge 700px respectivly) expand the width to the target size and the height gets chopped off.
Samples: Original, large, xLarge

Case 2: Images that are portrait and the width is smaller than the target size, expand the width to the target size and grow the height to meet the new width respectivly.
Samples: Original, large, xLarge

What I'm needing to do:

Case 1, If the width is smaller than the target size I want to keep the existing width, and height.
Case 2, Adjust the height to be the new target size wile maintaining the correct aspect ratio.

Any help would be grand. Also currently I do not have cacheing in place for the UI to use but that will come with time (maybe). Currently the system operates solely from the database with no dependance on the file system and I'm trying to keep it that way hence why I'm storing the thumbs in the database.

Thanks,
Tim

[Plater]

Is there a reason why you don't use the built in .GetThumbnailImage() function?

[tmeers]

The goal is to create images with an aspect ratio that is the same as the original image. Also doing it this way I can tweak the quality of the generated image and crank it as high or low as I need it to be, from garbage windows 3.1 looking images to as perfect as the original (or darn close).

The code works perfect for the 100px and 250px images, it's just when it starts to get larger than the original in width or height that it gets the glitch.

Tim

[Plater]

Well in those situations that you mentioned, could you use DrawImageUnscaled() to your advantage?

[tmeers]

Maybe? I'm really not sure because the images are generated correctly when the original is at least as large as the reduced sized image. Correct examples: Large http://gettinlucky.dyndns.org/large/612, Original http://gettinlucky.dyndns.org/612.ashx

How would the DrawImageUnscaled() even work?
Tim

[Plater]

Actually I guess I am still not clear what you want to do with the special cases.
I understand that if the original image is smaller then what you are trying to make, it can do wierd streching things.
What I would propose is that you compute the largest inscrbibed rectangle that matches the correct aspect ratio of the original image, but that still fits withen the thumbnail size bounds. Draw you image to that size(with stretching) and the draw it UNSCALED onto a blank image of the thumbnail size.
This will produce a white(or whatever background color you want) border in places where the original image did match the thumbnail size exactly.
Kind of like the way letterboxing works when you watch a widescreen format video on a regular tv.