Drawing without AntiAliasing?

Question

User-1219866711 posted

Hello,

I'm new to .NET and I wanted to draw a simple, vertical, 1px line on an image. However, the line always gets "smoothed" even though I tried everything in System.Drawing.Graphics to make it stop.

Here's an image (zoomed in) of what I mean:


Here's my code:

Bitmap map = new Bitmap("world.png");

Graphics g = Graphics.FromImage(map);
g.SmoothingMode = SmoothingMode.None;
g.InterpolationMode = InterpolationMode.NearestNeighbor;

g.DrawLine(new Pen(Color.FromArgb(255, 0, 0)), 10, 10, 10, 100);
g.Dispose();

//...save image...

Any help would be appreciated!

Answer 1

User1439985827 posted

I don't think the issue is that it is aliasing. Infact the default behavior is it won't alias. This code does what you want it to do:

Bitmap bmp = new Bitmap(500,500);
Graphics g = Graphics.FromImage(bmp);
g.DrawLine(new Pen(Color.Red, 5f), 10, 10, 10, 480);
g.Save();
bmp.Save(".\\out.bmp", ImageFormat.Bmp);

What I think you are seeing is possibly because you are saving it in a lossy compression like JPEG which causes it to appear to be aliased. Were you saving your image as a JPEG?

Answer 2

User-1219866711 posted

Wow, you're right. I can't believe I didn't think of that. I've been using the usual JPEG-lib before and also Photoshop's "Save as JPEG" but I have never ever seen a JPEG compression this bad. It works fine as BMP and PNG but even when setting the quality to "100" the .NET-implementation is really really bad. Is there any way to improve this or am I doing something wrong?

uint compression = 100;
ImageCodecInfo imageEncoderJpeg = null;

ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders();
foreach(ImageCodecInfo info in encoders)
{
	if(info.FormatID == ImageFormat.Jpeg.Guid)
	{
		imageEncoderJpeg = info;
		break;
	}
}

if(imageEncoderJpeg == null)
	return;

EncoderParameters parameters = new EncoderParameters(2);
parameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)compression);
parameters.Param[1] = new EncoderParameter(System.Drawing.Imaging.Encoder.Compression, (long)compression);

image.Save(path, imageEncoderJpeg, parameters);

Answer 3

User1439985827 posted

As far as I can tell, that is the way to produce the best quality images in JPEG using .NET. If this isn't suitable, I'd recommend another image format, or saving them as PNG/BMP and using a 3rd party tool to process them into JPEGs. 

Answer 4

User-1219866711 posted

I found out what the problem is. NET uses standard subsampling (4:2:2) when saving JPEGs, while every one else (e.g. Photoshop) uses no subsampling (4:4:4) when saving JPEG with a quality over 50%.

So, all I'd need to do is disable subsampling in NET - but that doesn't seem to be possible (maybe it's possible with Encoder.ChrominanceTable or Encoder.LuminanceTable but I have no idea how to do that and the documentation isn't helpful). I just spend searching the Internet with all possible keywords but it seems like only a handful of people wanted to do that and no one really succeeded (except one guy, but he didn't post an answer).

I'm hoping someone here might have a clue...

Answer 5

User1439985827 posted

Interesting discovery... I'll play around with it and see if I can find out. Thanks for the tip! 

Answer 6

User-1219866711 posted

Wow, thank you for your effort trying to solve this! It'd be pretty cool if you happen to find a solution :)

Answer 7

User1439985827 posted

Most solutions I was able to find were wrapping 3rd party libraries. There doesn't appear to be any known way, that I could find, to get the .NET Framework to do this itself.