Crea immagine anteprima

Question

Voglio visualizzare l'immagine di anteprima in una vista della griglia dal percorso del file. Come si genera quello del file .jpeg? Sto usando la lingua C# con asp.net.

Answer 1

si deve utilizzare GetThumbnailImage metodo nella classe Image:

https://msdn.microsoft.com/en-us/library/8t23aykb%28v=vs.110%29.aspx

Ecco un esempio di massima che prende un file di immagine e fa una miniatura da esso, quindi lo salva su disco.

Image image = Image.FromFile(fileName); 
Image thumb = image.GetThumbnailImage(120, 120,()=>false, IntPtr.Zero); 
thumb.Save(Path.ChangeExtension(fileName, "thumb")); 

Answer 2

Il seguente codice scriverà un'immagine proporzionale alla risposta, è possibile modificare il codice per il vostro scopo:

public void WriteImage(string path, int width, int height) 
{ 
    Bitmap srcBmp = new Bitmap(path); 
    float ratio = srcBmp.Width/srcBmp.Height; 
    SizeF newSize = new SizeF(width, height * ratio); 
    Bitmap target = new Bitmap((int) newSize.Width,(int) newSize.Height); 
    HttpContext.Response.Clear(); 
    HttpContext.Response.ContentType = "image/jpeg"; 
    using (Graphics graphics = Graphics.FromImage(target)) 
    { 
     graphics.CompositingQuality = CompositingQuality.HighSpeed; 
     graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; 
     graphics.CompositingMode = CompositingMode.SourceCopy; 
     graphics.DrawImage(srcBmp, 0, 0, newSize.Width, newSize.Height); 
     using (MemoryStream memoryStream = new MemoryStream()) 
     { 
      target.Save(memoryStream, ImageFormat.Jpeg); 
      memoryStream.WriteTo(HttpContext.Response.OutputStream); 
     } 
    } 
    Response.End(); 
} 

Answer 3

Ecco un esempio completo di come creare un'immagine più piccola (miniatura). Questo snippet ridimensiona l'immagine, la ruota quando necessario (se il telefono è tenuto in verticale) e riempie l'immagine se vuoi creare i pollici quadrati. Questo frammento crea un JPEG, ma può essere facilmente modificato per altri tipi di file. Anche se l'immagine fosse più piccola della dimensione massima consentita, l'immagine verrà comunque compressa e la sua risoluzione verrà alterata per creare immagini con lo stesso dpi e livello di compressione.

using System; 
using System.Drawing; 
using System.Drawing.Drawing2D; 
using System.Drawing.Imaging; 
using System.IO; 

//set the resolution, 72 is usually good enough for displaying images on monitors 
float imageResolution = 72; 

//set the compression level. higher compression = better quality = bigger images 
long compressionLevel = 80L; 


public Image resizeImage(Image image, int maxWidth, int maxHeight, bool padImage) 
{ 
    int newWidth; 
    int newHeight; 

    //first we check if the image needs rotating (eg phone held vertical when taking a picture for example) 
    foreach (var prop in image.PropertyItems) 
    { 
     if (prop.Id == 0x0112) 
     { 
      int orientationValue = image.GetPropertyItem(prop.Id).Value[0]; 
      RotateFlipType rotateFlipType = getRotateFlipType(orientationValue); 
      image.RotateFlip(rotateFlipType); 
      break; 
     } 
    } 

    //apply the padding to make a square image 
    if (padImage == true) 
    { 
     image = applyPaddingToImage(image, Color.Red); 
    } 

    //check if the with or height of the image exceeds the maximum specified, if so calculate the new dimensions 
    if (image.Width > maxWidth || image.Height > maxHeight) 
    { 
     double ratioX = (double)maxWidth/image.Width; 
     double ratioY = (double)maxHeight/image.Height; 
     double ratio = Math.Min(ratioX, ratioY); 

     newWidth = (int)(image.Width * ratio); 
     newHeight = (int)(image.Height * ratio); 
    } 
    else 
    { 
     newWidth = image.Width; 
     newHeight = image.Height; 
    } 

    //start the resize with a new image 
    Bitmap newImage = new Bitmap(newWidth, newHeight); 

    //set the new resolution 
    newImage.SetResolution(imageResolution, imageResolution); 

    //start the resizing 
    using (var graphics = Graphics.FromImage(newImage)) 
    { 
     //set some encoding specs 
     graphics.CompositingMode = CompositingMode.SourceCopy; 
     graphics.CompositingQuality = CompositingQuality.HighQuality; 
     graphics.SmoothingMode = SmoothingMode.HighQuality; 
     graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; 
     graphics.PixelOffsetMode = PixelOffsetMode.HighQuality; 

     graphics.DrawImage(image, 0, 0, newWidth, newHeight); 
    } 

    //save the image to a memorystream to apply the compression level 
    using (MemoryStream ms = new MemoryStream()) 
    { 
     EncoderParameters encoderParameters = new EncoderParameters(1); 
     encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, compressionLevel); 

     newImage.Save(ms, getEncoderInfo("image/jpeg"), encoderParameters); 

     //save the image as byte array here if you want the return type to be a Byte Array instead of Image 
     //byte[] imageAsByteArray = ms.ToArray(); 
    } 

    //return the image 
    return newImage; 
} 


//=== image padding 
public Image applyPaddingToImage(Image image, Color backColor) 
{ 
    //get the maximum size of the image dimensions 
    int maxSize = Math.Max(image.Height, image.Width); 
    Size squareSize = new Size(maxSize, maxSize); 

    //create a new square image 
    Bitmap squareImage = new Bitmap(squareSize.Width, squareSize.Height); 

    using (Graphics graphics = Graphics.FromImage(squareImage)) 
    { 
     //fill the new square with a color 
     graphics.FillRectangle(new SolidBrush(backColor), 0, 0, squareSize.Width, squareSize.Height); 

     //put the original image on top of the new square 
     graphics.DrawImage(image, (squareSize.Width/2) - (image.Width/2), (squareSize.Height/2) - (image.Height/2), image.Width, image.Height); 
    } 

    //return the image 
    return squareImage; 
} 


//=== get encoder info 
private ImageCodecInfo getEncoderInfo(string mimeType) 
{ 
    ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders(); 

    for (int j = 0; j < encoders.Length; ++j) 
    { 
     if (encoders[j].MimeType.ToLower() == mimeType.ToLower()) 
     { 
      return encoders[j]; 
     } 
    } 

    return null; 
} 


//=== determine image rotation 
private RotateFlipType getRotateFlipType(int rotateValue) 
{ 
    RotateFlipType flipType = RotateFlipType.RotateNoneFlipNone; 

    switch (rotateValue) 
    { 
     case 1: 
      flipType = RotateFlipType.RotateNoneFlipNone; 
      break; 
     case 2: 
      flipType = RotateFlipType.RotateNoneFlipX; 
      break; 
     case 3: 
      flipType = RotateFlipType.Rotate180FlipNone; 
      break; 
     case 4: 
      flipType = RotateFlipType.Rotate180FlipX; 
      break; 
     case 5: 
      flipType = RotateFlipType.Rotate90FlipX; 
      break; 
     case 6: 
      flipType = RotateFlipType.Rotate90FlipNone; 
      break; 
     case 7: 
      flipType = RotateFlipType.Rotate270FlipX; 
      break; 
     case 8: 
      flipType = RotateFlipType.Rotate270FlipNone; 
      break; 
     default: 
      flipType = RotateFlipType.RotateNoneFlipNone; 
      break; 
    } 

    return flipType; 
} 


//== convert image to base64 
public string convertImageToBase64(Image image) 
{ 
    using (MemoryStream ms = new MemoryStream()) 
    { 
     //convert the image to byte array 
     image.Save(ms, ImageFormat.Jpeg); 
     byte[] bin = ms.ToArray(); 

     //convert byte array to base64 string 
     return Convert.ToBase64String(bin); 
    } 
} 

Per gli utenti asp.net un piccolo esempio di come caricare un file, ridimensionarla e visualizzare il risultato nella pagina.

//== the button click method 
protected void Button1_Click(object sender, EventArgs e) 
{ 
    //check if there is an actual file being uploaded 
    if (FileUpload1.HasFile == false) 
    { 
     return; 
    } 

    using (Bitmap bitmap = new Bitmap(FileUpload1.PostedFile.InputStream)) 
    { 
     try 
     { 
      //start the resize 
      Image image = resizeImage(bitmap, 256, 256, true); 

      //to visualize the result, display as base64 image 
      Label1.Text = "<img src=\"data:image/jpg;base64," + convertImageToBase64(image) + "\">"; 

      //save your image to file sytem, database etc here 
     } 
     catch (Exception ex) 
     { 
      Label1.Text = "Oops! There was an error when resizing the Image.<br>Error: " + ex.Message; 
     } 
    } 
}