Drawing a GIF with System.Drawing

Question

User1942128046 posted

Hi everyone,

I'm using some asp.net pages to output an files of content type GIF. Including a path to this aspx in the 'src' attribute of an 'img' tag in the html markup, will display the gif on any page, including html. So I have a page called 'displayImage.html', and the markup includes this code:

<img src="generarLogo.aspx" alt="Logo" >

This works fine. My problem is the quality of the logo. It seems like it's displaying a gif with a reduced amount of colors, because I see some of the colors dotted, creating a bad quality look.

My C# code would be something like this:

Image originalImg = Image.FromFile(Server.MapPath("logo.gif"));
Bitmap image1 = new Bitmap(originalImg);

this.Response.Clear();
this.Response.ContentType = "image/gif";

image1.Save(this.Response.OutputStream, ImageFormat.Gif);

I have also tried adding a Palette with this method:

image1.Palette = GetColorPalette(256);

protected ColorPalette GetColorPalette(uint nColors)
    {
        // Assume monochrome image. (2 colors)
        PixelFormat bitscolordepth = PixelFormat.Format1bppIndexed;
        ColorPalette palette;    // The Palette we are stealing
        Bitmap bitmap;     // The source of the stolen palette

        // Determine number of colors.
        if (nColors > 2)
            bitscolordepth = PixelFormat.Format4bppIndexed;
        if (nColors > 16)
            bitscolordepth = PixelFormat.Format8bppIndexed;

        // Make a new Bitmap object to get its Palette.
        bitmap = new Bitmap(1, 1, bitscolordepth);
        palette = bitmap.Palette;
        bitmap.Dispose();           

        return palette;             
    }

But this doesn't improve the quality of my GIF image. I got this little method from msdn documentation.

Answer 1

User-1659704165 posted

Hi,


public void CreateGif()
    {
        //Variable declaration
        StringCollection stringCollection = new StringCollection();
        MemoryStream memoryStream;
        BinaryWriter binaryWriter;
        System.Drawing.Image image;
        Byte[] buf1;
        Byte[] buf2;
        Byte[] buf3;
        //Variable declaration

      //  stringCollection = a_StringCollection_containing_images;

        stringCollection.Add(@"C:\Ok.gif");

      //  stringCollection.Add(@"C:\ok.gif");

        Response.ContentType = "Image/gif";
        memoryStream = new MemoryStream();
        buf2 = new Byte[19];
        buf3 = new Byte[8];
        buf2[0] = 33;  //extension introducer
        buf2[1] = 255; //application extension
        buf2[2] = 11;  //size of block
        buf2[3] = 78;  //N
        buf2[4] = 69;  //E
        buf2[5] = 84;  //T
        buf2[6] = 83;  //S
        buf2[7] = 67;  //C
        buf2[8] = 65;  //A
        buf2[9] = 80;  //P
        buf2[10] = 69; //E
        buf2[11] = 50; //2
        buf2[12] = 46; //.
        buf2[13] = 48; //0
        buf2[14] = 3;  //Size of block
        buf2[15] = 1;  //
        buf2[16] = 0;  //
        buf2[17] = 0;  //
        buf2[18] = 0;  //Block terminator
        buf3[0] = 33;  //Extension introducer
        buf3[1] = 249; //Graphic control extension
        buf3[2] = 4;   //Size of block
        buf3[3] = 9;   //Flags: reserved, disposal method, user input, transparent color
        buf3[4] = 10;  //Delay time low byte
        buf3[5] = 3;   //Delay time high byte
        buf3[6] = 255; //Transparent color index
        buf3[7] = 0;   //Block terminator
        binaryWriter = new BinaryWriter(Response.OutputStream);
        for (int picCount = 0; picCount < stringCollection.Count; picCount++)
        {
            image = Bitmap.FromFile(stringCollection[picCount]);
            image.Save(memoryStream, ImageFormat.Gif);
            buf1 = memoryStream.ToArray();

            if (picCount == 0)
            {
                //only write these the first time....
                binaryWriter.Write(buf1, 0, 781); //Header & global color table
                binaryWriter.Write(buf2, 0, 19); //Application extension
            }

            binaryWriter.Write(buf3, 0, 8); //Graphic extension
            binaryWriter.Write(buf1, 789, buf1.Length - 790); //Image data

            if (picCount == stringCollection.Count - 1)
            {
                //only write this one the last time....
                binaryWriter.Write(";"); //Image terminator
            }

            memoryStream.SetLength(0);
        }
        binaryWriter.Close();
        Response.End();
    }

OR

http://bloggingabout.net/blogs/rick/archive/2005/05/10/3830.aspx

chk the above link

Answer 2

User1942128046 posted

Thanks qwe123kids, I will try this. Not as straight forward as I initially thought.. .