如何从硬盘获取图像，调整图像大小并将其添加到列表中 <image> 快速？

Question

I'm doing now

imageslist = new List<Image>();
            foreach (string myFile in
                      Directory.GetFiles(dir, "*.bmp", SearchOption.AllDirectories))
            {

                Bitmap bmp = new Bitmap(myFile);
                imageslist.Add(bmp);
            }

But the foreach is very slow. And i have this method to resize the images i want to resize them before adding them to the list

public static Bitmap ResizeImage(Image image, int width, int height)
        {
            var destRect = new Rectangle(0, 0, width, height);
            var destImage = new Bitmap(width, height);

            destImage.SetResolution(image.HorizontalResolution, image.VerticalResolution);

            using (var graphics = Graphics.FromImage(destImage))
            {
                graphics.CompositingMode = CompositingMode.SourceCopy;
                graphics.CompositingQuality = CompositingQuality.HighQuality;
                graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
                graphics.SmoothingMode = SmoothingMode.HighQuality;
                graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

                using (var wrapMode = new ImageAttributes())
                {
                    wrapMode.SetWrapMode(WrapMode.TileFlipXY);
                    graphics.DrawImage(image, destRect, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, wrapMode);
                }
            }

            return destImage;
        }

In the end i want to have in the List<Image> imageslist all the images in size of 100,100 resolution and the images are now 24 bit depth should i try to change it also or 24 bit is fine ?

Answer 1

I have two improvements:

1. Use Directory.EnumerateFiles instead of Directory.GetFiles , you will not have to wait until all results will be returned, it will be lazy evaluated
2. Run the resizing in parallel (in my example below using AsParallel extension method)

var imageslist = Directory.EnumerateFiles(dir, "*.bmp", SearchOption.AllDirectories)
    .AsParallel()
    .Select(path => new Bitmap(path))
    .Select(bmp => ResizeImage(bmp, 100, 100))
    .ToList();

Remember to verify the speed of the parallel solution because only after comparing it with non-parallel solution (run the code without AsParallel ) you will be sure that it improves performance in your case.