通過定義寬度在 .NET C# 中創建縮略圖

Question

我在我的網站中使用以下代碼來創建縮略圖：

string furl = "~/images/thumbs/" + matchString;
lBlogThumb.ImageUrl = GetThumbnailView(furl, 200, 200);


private string GetThumbnailView(string originalImagePath, int height, int width)
        {
            //Consider Image is stored at path like "ProductImage\\Product1.jpg"

            //Now we have created one another folder ProductThumbnail to store thumbnail image of product.
            //So let name of image be same, just change the FolderName while storing image.
            string thumbnailImagePath = originalImagePath.Replace("thumbs", "thumbs2");
            //If thumbnail Image is not available, generate it.
            if (!System.IO.File.Exists(Server.MapPath(thumbnailImagePath)))
            {
                System.Drawing.Image imThumbnailImage;
                System.Drawing.Image OriginalImage = System.Drawing.Image.FromFile(Server.MapPath(originalImagePath));
                imThumbnailImage = OriginalImage.GetThumbnailImage(width, height,
                             new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero);

                imThumbnailImage.Save(Server.MapPath(thumbnailImagePath), System.Drawing.Imaging.ImageFormat.Jpeg);

                imThumbnailImage.Dispose();
                OriginalImage.Dispose();
            }
            return thumbnailImagePath;
        }

public bool ThumbnailCallback() { return false; }

我想更改此代碼，並且能夠創建僅定義寬度的縮略圖。 我想到的實際上是像裁剪/調整圖像大小，使用靜態寬度，保持它的比例。 那可能嗎;

Answer 1

你提到調整大小和裁剪。 如果您希望縮略圖高度隨固定寬度變化，那么已經提供的答案將適合您。

提到裁剪讓我覺得你可能想要一個固定的縮略圖大小，填充寬度並裁剪掉任何溢出的垂直部分。 如果是這種情況，您將需要做更多的工作。 我最近需要類似的東西，這就是我想出的。

這將創建一個原始縮略圖，其大小和裁剪方式使源圖像完全填充目標縮略圖，裁剪任何溢出。 即使原始和縮略圖的縱橫比不同，縮略圖內也不會有邊框。

public System.Drawing.Image CreateThumbnail(System.Drawing.Image image, Size thumbnailSize)
{
    float scalingRatio = CalculateScalingRatio(image.Size, thumbnailSize);

    int scaledWidth = (int)Math.Round((float)image.Size.Width * scalingRatio);
    int scaledHeight = (int)Math.Round((float)image.Size.Height * scalingRatio);
    int scaledLeft = (thumbnailSize.Width - scaledWidth) / 2;
    int scaledTop = (thumbnailSize.Height - scaledHeight) / 2;

    // For portrait mode, adjust the vertical top of the crop area so that we get more of the top area
    if (scaledWidth < scaledHeight && scaledHeight > thumbnailSize.Height)
    {
        scaledTop = (thumbnailSize.Height - scaledHeight) / 4;
    }

    Rectangle cropArea = new Rectangle(scaledLeft, scaledTop, scaledWidth, scaledHeight);

    System.Drawing.Image thumbnail = new Bitmap(thumbnailSize.Width, thumbnailSize.Height);
    using (Graphics thumbnailGraphics = Graphics.FromImage(thumbnail))
    {
        thumbnailGraphics.CompositingQuality = CompositingQuality.HighQuality;
        thumbnailGraphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
        thumbnailGraphics.SmoothingMode = SmoothingMode.HighQuality;
        thumbnailGraphics.DrawImage(image, cropArea);
    }
    return thumbnail;
}

private float CalculateScalingRatio(Size originalSize, Size targetSize)
{
    float originalAspectRatio = (float)originalSize.Width / (float)originalSize.Height;
    float targetAspectRatio = (float)targetSize.Width / (float)targetSize.Height;

    float scalingRatio = 0;

    if (targetAspectRatio >= originalAspectRatio)
    {
        scalingRatio = (float)targetSize.Width / (float)originalSize.Width;
    }
    else
    {
        scalingRatio = (float)targetSize.Height / (float)originalSize.Height;
    }

    return scalingRatio;
}

要與您的代碼一起使用，您可以用以下代碼替換對OriginalImage.GetThumbnailImage的調用：

imThumbnailImage = CreateThumbnail(OriginalImage, new Size(width, height));

請注意，對於縱向圖像，此代碼實際上會將縮略圖的視口在原始圖像上略微移動。 這樣做是為了在創建縮略圖時人像拍攝不會導致無頭軀干。 如果您不想要該邏輯，只需刪除“縱向模式”注釋后的if塊。

Answer 2

讓我們讓 originalWidth = 原始圖像寬度和 thumbWidth。 您可以簡單地將 thumbWidth 選擇為您想要的值，然后計算thumbHeigth=originalHeigth*thumbWidth/originalWidth

Answer 3

我厭倦了需要這樣做並創建了一個可以輕松執行此操作的庫：鏈接到文檔和下載

Answer 4

一個沒有舍入且縮略圖寬度為 140 的基本示例，在“文件”下方是從 ASP.Net FileUpload 控件上傳的 HttpPostedFile，HttpPostedFile 公開了一個流。

// Save images to disk.
using (System.Drawing.Image image = System.Drawing.Image.FromStream(file.InputStream))
using (System.Drawing.Image thumbnailImage = image.GetThumbnailImage(140, Convert.ToInt32((image.Height / (image.Width / 140))), null, IntPtr.Zero))
{
    if (image != null)
    {
        image.Save(imageFilePath);
        thumbnailImage.Save(thumbnailImagePath); 
    }
    else
        throw new ArgumentNullException("Image stream is null");
}