Unable to create a scalable png image using C# in .NET

问题

I am trying to create an image based on a string. The image needs to be raster (otherwise it will lose resolution if I need to zoom out). I am using the following code:

Bitmap bitmapimage = new Bitmap(200, 100);
Graphics bitmapGraphics = Graphics.FromImage(bitmapimage );   
bitmapGraphics .DrawString("test", new Font("Arial",50), Brushes.Black, new Point(0, 0));              
bitmapimage .Save("Image.png", System.Drawing.Imaging.ImageFormat.png);
textPictureBox.Image = bitmapimage ;

What I get is an image like this (after zooming):

Why is this?

回答1:

I think you misunderstand what "raster" means. Raster images are grids, with one pixel at each grid location. When you zoom on a raster image far enough the grid becomes clearly visible, even with techniques like anti-aliasing.

Vector graphics, on the other hand, are algorithm based. They store instructions on how to reproduce an image on a given canvas. When you zoom a vector image, the image will stay sharp because it's still following the instruction, rather than simply scaling the previous rendering.

All of the major image types (bmp, gif, png, jpeg) are raster types, and do not support vector graphics. The png image is your example is rastered... in fact, it's impossible to create a png image this is not rastered. An example of a vector image is certain font types or Photoshop (psd) files (sort of... in practice, Photoshop files tend to be more raster than vector in the end).

In this case, probably the easiest solution is to draw the image very large in the first place... large enough that you won't need to zoom in, and use a large enough font to fill the space. You also need to make sure that you are using a font that is fully vector-drawn.

回答2:

Try using Vector Basic graphics, if you using it you will not have problems if you zoom in or out

o Vector Graphics in C# (MSDN)

o Example Project (MSDN)

回答3:

Vector graphics are scalable, raster are not.
Text fonts are scalable (unless you use bitmap fonts), but once you draw a string on a bitmap this text becomes a raster image, so it can't be scaled anymore. Thus, if you need to draw text on a bitmap try to use a large image and use anti-aliased text (again, this image won't be scalable but if it's large enough there will be no need to zoom it in).

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Here is a modified version of your code (the text will be as large as the PNG image):

add the following using:

using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.Drawing.Text;

Add this line into your form (as a private class field):

        Random rnd = new Random();

the rest of the code:

        int scl = rnd.Next(100, 451);
        Bitmap bitmapimage = new Bitmap(2 * scl, scl);
        Graphics bitmapGraphics = Graphics.FromImage(bitmapimage);
        bitmapGraphics.CompositingMode = CompositingMode.SourceOver;
        bitmapGraphics.TextRenderingHint = TextRenderingHint.AntiAlias;  // text is now anti-aliased
        bitmapGraphics.SmoothingMode = SmoothingMode.HighQuality;
        bitmapGraphics.DrawString("test", new Font("Arial", scl * 9 / 10, GraphicsUnit.Pixel), Brushes.Black, new Point(0, 0));
        bitmapimage.Save("Image.png", ImageFormat.Png);
        bitmapGraphics.Dispose();

By the way, if you draw text on a printer's Graphics object, this text is still scalable since printers don't use pixels (but if you draw a raster image on a printer's Graphics object, this image will get blurry if it's zoomed in).

来源：https://stackoverflow.com/questions/14343176/unable-to-create-a-scalable-png-image-using-c-sharp-in-net