I am trying to generate a thumbnail from the base64string
. I am storing the image in a table and am trying to generate a thumbnail from the base64string
being stored.
I am able to generate the thumbnail if I provide a path to the image, but that will not work in my case.
This is the working solution of generating a thumbnail from an image path:
protected void GenerateThumbnail(object sender, EventArgs e)
{
string path = Server.MapPath("../src/img/myImage.png");
System.Drawing.Image image = System.Drawing.Image.FromFile(path);
using (System.Drawing.Image thumbnail = image.GetThumbnailImage(100, 100, new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero))
{
using (MemoryStream memoryStream = new MemoryStream())
{
thumbnail.Save(memoryStream, ImageFormat.Png);
Byte[] bytes = new Byte[memoryStream.Length];
memoryStream.Position = 0;
memoryStream.Read(bytes, 0, (int)bytes.Length);
string base64String = Convert.ToBase64String(bytes, 0, bytes.Length);
Image2.ImageUrl = "data:image/png;base64," + base64String;
Image2.Visible = true;
}
}
}
Can anyone provide any advice on how to use the base64string
instead of the image path the generate thumbnail?
Assuming, b64
is the base64 string, you can convert it to a byte array and use that to construct the starting image.
byte[] bytes = Convert.FromBase64String(b64);
using (MemoryStream ms = new MemoryStream(bytes))
{
Bitmap thumb = new Bitmap(100, 100);
using (Image bmp = Image.FromStream(ms))
{
using (Graphics g = Graphics.FromImage(thumb))
{
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.CompositingQuality = CompositingQuality.HighQuality;
g.SmoothingMode = SmoothingMode.HighQuality;
g.DrawImage(bmp, 0, 0, 100, 100);
}
}
// a picturebox to show/test the result
picOut.Image = thumb;
}
Be sure to dispose of the thumb when you are done with it.
Mixed few tricks found online. (one from @Plutonix)
string ThumbNailBase64 = ResizeBase64ImageString(YourBase64String,200, 300);
base64 Input => resize => base64
You get the desired thumbnail with auto aspect ratio .
public static string ResizeBase64ImageString(string Base64String, int desiredWidth, int desiredHeight)
{
Base64String = Base64String.Replace("data:image/png;base64,", "");
// Convert Base64 String to byte[]
byte[] imageBytes = Convert.FromBase64String(Base64String);
using (MemoryStream ms = new MemoryStream(imageBytes))
{
// Convert byte[] to Image
ms.Write(imageBytes, 0, imageBytes.Length);
Image image = Image.FromStream(ms, true);
var imag = ScaleImage(image, desiredWidth, desiredHeight);
using (MemoryStream ms1 = new MemoryStream())
{
//First Convert Image to byte[]
imag.Save(ms1, imag.RawFormat);
byte[] imageBytes1 = ms1.ToArray();
//Then Convert byte[] to Base64 String
string base64String = Convert.ToBase64String(imageBytes1);
return "data:image/png;base64,"+base64String;
}
}
}
public static Image ScaleImage(Image image, int maxWidth, int maxHeight)
{
var ratioX = (double)maxWidth / image.Width;
var ratioY = (double)maxHeight / image.Height;
var ratio = Math.Min(ratioX, ratioY);
var newWidth = (int)(image.Width * ratio);
var newHeight = (int)(image.Height * ratio);
var newImage = new Bitmap(newWidth, newHeight);
using (var graphics = Graphics.FromImage(newImage))
graphics.DrawImage(image, 0, 0, newWidth, newHeight);
return newImage;
}
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