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Old January 23rd, 2007, 04:42 AM
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Default uploading/resizing (transparant) images in C#

hi There,

I am busy with a web application in C#. Customers will have the possibility to upload there company logo for there profile.

Uploading/resizing images is no problem butt when the images are gif or png with transparancy the image is really ugly after resizing. The transparancy gets black in stead of transparant.

I hope there is a default way to avoid this problem. I know there is a default way in php so maybe someone can help me on this one.

Thank already! (Sorry, the code comments are in Dutch language)

This is the code I use:

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Imaging;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;

namespace LibraPortal.UploadImage
    public class UploadForm : System.Web.UI.Page

        //Maximale hoogte van de thumbnail indien het in verhouding een hoog plaatje is 
        public const int ThumbnailSizeHigh = 60 ;

        //Maximale breedte van het plaatje indien het in verhouding een breed plaatje is
        public const int ThumbnailSizeWidth = 150 ;

        //Maximale breedte van het plaatje indien het in verhouding een redelijk vierkant plaatje is
        public const int ThumbnailSizeWidthSquare = 70;

        public double ThumbnailWidth ;
        public double ThumbnailHeight;
        public double ThumbnailRatio;

        //Werkgever ID (Deze wordt meegenomen in de bestandsnaam om overschrijving te voorkomen)
        public string EmpID;

        protected HtmlGenericControl message;

        protected HtmlInputFile file;
        protected HtmlInputFile file1;
        protected HtmlInputFile file2;

        private void Page_Load(object sender, System.EventArgs e)
            if (IsPostBack)
                message.Attributes.Add("align", "left");


        private void AppendMessage(string msg)
            message.Controls.Add(new LiteralControl(msg));

        private void DisplayImageInfo(HttpPostedFile image)
            //Javascripts die ervoor zorgen dat de juiste waardes naar het parent window worden verplaatst
            //en het upload venster wordt gesloten.
            AppendMessage(String.Format("<script language='javascript'>opener.setVeld1('{0}'); </script>", System.IO.Path.GetFileName(image.FileName)));
            AppendMessage(String.Format("<script language='javascript'>window.close();</script>"));             

        private bool IsImage(HttpPostedFile file)
            //Controleren of het geslecteerde bestand een plaatje is
            if(file != null && Regex.IsMatch(file.ContentType, "image/\\S+") &&
                file.ContentLength > 0)
                return true;

            //Bestand is geen plaatje, dus hiervan een melding geven
            AppendMessage(String.Format("U heeft geen bestand geselecteerd of er is een verkeerd bestandstype geupload. Alleen jpg, bmp en gif is toegestaan."));
            return false;

        protected void UploadImageWithNoRestrictions(HttpPostedFile file)

        protected Bitmap GetResizedImage(Bitmap bitmap)
            //Ratio berekenen (breedte/hoogte)
            ThumbnailRatio = Convert.ToDouble(bitmap.Width) / Convert.ToDouble(bitmap.Height);

            //Plaatje is in verhouding een breed plaatje
            if (ThumbnailRatio > 1.7)
                ThumbnailWidth = ThumbnailSizeWidth;
                ThumbnailHeight = ThumbnailSizeWidth / ThumbnailRatio;
            //Plaatje is in verhouding redelijk vierkant
            else if ((ThumbnailRatio < 1.7) && (ThumbnailRatio > 1))
                ThumbnailWidth = ThumbnailSizeWidthSquare;
                ThumbnailHeight = ThumbnailSizeWidthSquare / ThumbnailRatio;
            //Plaatje is in verhouding hoog
                ThumbnailHeight = ThumbnailSizeHigh;
                ThumbnailWidth = ThumbnailSizeHigh / ThumbnailRatio;

            return new Bitmap(bitmap, Convert.ToInt32(ThumbnailWidth), Convert.ToInt32(ThumbnailHeight));

        protected void UploadImage(HttpPostedFile file)

            //Werkgever ID meegeven in de bestandsnaam om overschrijving te voorkomen
            EmpID = Request.QueryString["gid"];

            //Opslaan van originele plaatje
            string fileName =
                file.FileName.Substring(file.FileName.LastIndexOf('\\') + 1);
            string filePath = MapPath("logos/" + EmpID + "_" + fileName);


            using(System.Drawing.Image image =

            //Opslaan van geresizede plaatje
            using (Bitmap bitmap = GetResizedImage((Bitmap) image))
                bitmap.Save(MapPath("logos/t__" + EmpID + "_" + fileName), image.RawFormat);              

            //Na het opslaan van het geresizede plaatje kan het originele plaatje verwijderd worden
            File.Delete(MapPath("logos/" + EmpID + "_" + fileName));            

        #region Web Form Designer generated code
        override protected void OnInit(EventArgs e)
            // CODEGEN: This call is required by the ASP.NET Web Form Designer.

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
            this.Load += new System.EventHandler(this.Page_Load);
Old February 19th, 2007, 08:53 PM
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Hi. I am doing something similar to that. I am looking for a solution but I don't find anything yet. I'm not sure if you have found a way to do this.
I hope you can help me.

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