Why does DrawString look so crappy?

Question

I am trying to add a text scale to a color image. The agcScale.jpg image (below) is 2 winform labels on the top and bottom and 2 winform pictureboxes on the left and right. The exact same code was used to produce the strings in the right and left pictureboxes, the only difference is that pictureBoxAgcVscale contains only the strings. Why does DrawString in pictureBoxAgc look fine but DrawString in pictureBoxAgcVscale look so bad? I can probably fix pictureBoxAgcVscale by doing a bmp.SetPixel for each pixel but that seems like the wrong way to fix this.

private void DisplayAgcVscale(double min, double max)
{
    var bmp = new Bitmap(pictureBoxAgcVscale.Width, pictureBoxAgcVscale.Height);
    var c = (max - min) / bmp.Height;
    using (var g = Graphics.FromImage(bmp))
    {
        var font = new Font("Microsoft Sans Serif", 8.25F);
        var y1 = bmp.Height / 10;
        for (var y = y1; y < bmp.Height; y += y1)
        {
            var agc = y * c + min;
            var text = agc.ToString("#0.000V");
            var h = bmp.Height - y - font.Height / 2;
            g.DrawString(text, font, Brushes.Black, 0, h);
        }
    }
    pictureBoxAgcVscale.Image = bmp;
}

Can you edit this into a short but complete program? I'll give it a go myself, but if you could do it it would be simpler... — Jon Skeet, Oct 25 '11 at 16:15
@JoshuaEvensen I'd guess it's anti aliasing (together with not clearing the background) than causes this problem. — CodesInChaos, Oct 25 '11 at 16:35
Hi jacknad. This is very relevant to what I am doing. I was wondering if this is open-sourced so I could take a look at how you make this graph legend? — theGreenCabbage, Jan 09 '14 at 15:18

score 15 · Accepted Answer · answered Oct 25 '11 at 16:26

15

You are drawing black text on a transparent background. The anti-aliasing pixels are fading from black to black, no choice, turning the letters into blobs. It works for the text on the left because you draw the pixels first.

You forgot g.Clear().

answered Oct 25 '11 at 16:26

Hans Passant

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`g.Clear` on a blank image? Have to try this now. – leppie Oct 25 '11 at 16:30
Thanks a million. g.Clear() works fine, but it was counter intuitive (to me) that `g.Clear()` is needed for a `transparent` background. – jacknad Oct 25 '11 at 21:29
Thanks..I resolve bad text quality with this idea of g.Clear().. I had to write text directly on image. g.Clear() helped me. In my case I could not use g.clear() directly on image loaded in Graphics object. First I create new empty bitmap, then I use g.Clear(), then I write text on this new bitmap and at the end I overlay this bitmap on original image. – t4taurus Jan 24 '17 at 21:07

score 0 · Answer 2 · answered May 11 '22 at 16:22

I had a similar issue, but in a listbox, and it wasn't resolved by clearing the rectangle. I had to apply a "TextRenderingHint":

e.Graphics.TextRenderingHint = TextRenderingHint.AntiAlias;
e.Graphics.DrawString(listText, myFont, myBrush, e.Bounds, StringFormat.GenericDefault);

Why does DrawString look so crappy?

2 Answers2