Question

asp.net 图片上传 自动修改图片的尺寸

我想在用户上传图片的时候,自动修改用户图片的尺寸,请问这个怎么实现..
就是要图片变小,或者变大,不变形的效果.

Answer 1

给你一段代码吧：
///originalImage:原始的图像
///thumbnailPath:目标图像的路径
///DestSize:目标大小
public static byte[] MakeThumbnail(Image originalImage, string thumbnailPath , Size DestSize)
{
Size size = GetLogoImageActualDesiredSize(originalImage.Size, DestSize);

int towidth = size.Width;
int toheight = size.Height;

int x = 0;
int y = 0;
int ow = originalImage.Width;
int oh = originalImage.Height;

//create a new bmp picutre object
Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

//create a new graphics
Graphics g = System.Drawing.Graphics.FromImage(bitmap);

//set interpolation way of high quality
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

//set smooothing mode of high quality
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

g.Clear(Color.Transparent);

g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
new Rectangle(x, y, ow, oh),
GraphicsUnit.Pixel);
try
{
FileStream fs = new FileStream(thumbnailPath, FileMode.Create);
bitmap.Save(fs, System.Drawing.Imaging.ImageFormat.Jpeg);
fs.Close();
MemoryStream ms = new MemoryStream();
bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
byte[] byteArray = ms.ToArray();
ms.Close();
return byteArray;
}
catch (System.Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
}

public static Size GetLogoImageActualDesiredSize(Size originLogoSize, Size desiredLogoSize)
{
if (originLogoSize.Width <= 0 || originLogoSize.Height <= 0)
throw new ArgumentOutOfRangeException("originLogoSize", "Width or Height of size is smaller or equal to zero");
if (desiredLogoSize.Width <= 0 || desiredLogoSize.Height <= 0)
throw new ArgumentOutOfRangeException("desiredLogoSize", "Width or Height of size is smaller or equal to zero");

float scaleX = (float)desiredLogoSize.Width / originLogoSize.Width;
float scaleY = (float)desiredLogoSize.Height / originLogoSize.Height;
float scale = Math.Min(scaleX, scaleY);
int width = Convert.ToInt32(Math.Truncate(originLogoSize.Width * scale));
int height = Convert.ToInt32(Math.Truncate(originLogoSize.Height * scale));
return new Size(width, height);
}

Answer 2

/**/
/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="originalImagePath">源图路径（物理路径）</param>
/// <param name="thumbnailPath">缩略图路径（物理路径）</param>
/// <param name="width">缩略图宽度</param>
/// <param name="height">缩略图高度</param>
/// <param name="mode">生成缩略图的方式</param>
public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
{
System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);

int towidth = width;
int toheight = height;

int x = 0;
int y = 0;
int ow = originalImage.Width;
int oh = originalImage.Height;

switch (mode)
{
case "HW"://指定高宽缩放（可能变形）
break;
case "W"://指定宽，高按比例
toheight = originalImage.Height * width / originalImage.Width;
break;
case "H"://指定高，宽按比例
towidth = originalImage.Width * height / originalImage.Height;
break;
case "Cut"://指定高宽裁减（不变形）
if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
{
oh = originalImage.Height;
ow = originalImage.Height * towidth / toheight;
y = 0;
x = (originalImage.Width - ow) / 2;
}
else
{
ow = originalImage.Width;
oh = originalImage.Width * height / towidth;
x = 0;
y = (originalImage.Height - oh) / 2;
}
break;
default:
break;
}

//新建一个bmp图片
System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

//新建一个画板
System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);

//设置高质量插值法
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

//设置高质量,低速度呈现平滑程度
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

//清空画布并以透明背景色填充
g.Clear(System.Drawing.Color.Transparent);

//在指定位置并且按指定大小绘制原图片的指定部分
g.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
new System.Drawing.Rectangle(x, y, ow, oh),
System.Drawing.GraphicsUnit.Pixel);

try
{
//以jpg格式保存缩略图
bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
}
catch (System.Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
}