Crea un’immagine di anteprima

Voglio visualizzare l’immagine di anteprima in una griglia dalla posizione del file. Come si genera quello del file .jpeg ? Sto usando il linguaggio C# con asp.net .

Devi utilizzare il metodo GetThumbnailImage nella class Image :

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

Ecco un esempio approssimativo che prende un file immagine e ne fa un’immagine in miniatura, 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")); 

Il seguente codice scriverà un’immagine in proporzione alla risposta, puoi modificare il codice per il tuo 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(); } 

Ecco un esempio completo di come creare un’immagine più piccola (miniatura). Questo snippet ridimensiona l’immagine, lo ruota quando necessario (se un telefono è tenuto in verticale) e riempie l’immagine se si desidera creare 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 di asp.net un piccolo esempio di come caricare un file, ridimensionarlo e visualizzare il risultato sulla 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 = ""; //save your image to file sytem, database etc here } catch (Exception ex) { Label1.Text = "Oops! There was an error when resizing the Image.
Error: " + ex.Message; } } }

Ecco un esempio per convertire immagini ad alta risoluzione in dimensioni miniatura-

 protected void Button1_Click(object sender, EventArgs e) { //---------- Getting the Image File System.Drawing.Image img = System.Drawing.Image.FromFile(Server.MapPath("~/profile/Avatar.jpg")); //---------- Getting Size of Original Image double imgHeight = img.Size.Height; double imgWidth = img.Size.Width; //---------- Getting Decreased Size double x = imgWidth / 200; int newWidth = Convert.ToInt32(imgWidth / x); int newHeight = Convert.ToInt32(imgHeight / x); //---------- Creating Small Image System.Drawing.Image.GetThumbnailImageAbort myCallback = new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback); System.Drawing.Image myThumbnail = img.GetThumbnailImage(newWidth, newHeight, myCallback, IntPtr.Zero); //---------- Saving Image myThumbnail.Save(Server.MapPath("~/profile/NewImage.jpg")); } public bool ThumbnailCallback() { return false; } 

Fonte- http://iknowledgeboy.blogspot.in/2014/03/c-creating-thumbnail-of-large-image-by.html