ImageMagick.net Background colour of annotated text/label always black - imagemagick

Question

I am trying to add a label/annotation text (where the background colour of the text is transparent) to an existing image.
I have tried a couple of different approaches but I keep getting a black background colour.
If anyone could point me in the right direction, I would greatly appreciate it.
Attempt 1:
using (var images = new MagickImageCollection())
using (var img = new MagickImage(imgBytes))
{
img.Resize(imageDto.Width, imageDto.Height);
using (var imgText = new MagickImage(MagickColors.None, imageDto.Width, imageDto.Height))
{
var labelSettings = new MagickReadSettings()
{
BackgroundColor = MagickColors.None,
Font = "Arial",
FontPointsize = imageDto.FontSize,
FillColor = MagickColors.Blue,
BorderColor = MagickColors.None,
};
imgText.Read("label:" + imageDto.WatermarkText, labelSettings);
img.Composite(imgText, Gravity.South);
img.Write($"{Guid.NewGuid().ToString()}.png");
return img.ToBase64();
}
}
Attempt 2:
using (var img = new MagickImage(imgBytes))
{
img.Resize(imageDto.Width, imageDto.Height);
// Load the original image and add it to the collection.
images.Add(img);
// Text label watermark settings
var labelSettings = new MagickReadSettings()
{
BackgroundColor = new MagickColor(MagickColors.Transparent),
Font = "Arial",
FontPointsize = imageDto.FontSize,
FillColor = MagickColors.Blue
};
// Create the label image.
var label = new MagickImage($"label:{imageDto.WatermarkText}", labelSettings);
// Extent the width of the label to match the width of the original image.
label.Extent(img.Width, 0, Gravity.Center);
label.Transparent(MagickColors.Black);
// Add the label to the collection.
images.Add(label);
// Append the images to create the output image.
using (var result = images.AppendVertically())
{
result.Write($"{Guid.NewGuid().ToString()}.png");
return result.ToBase64();
}
}
Both attempts produce the same image with a black background (in the area where the text was added to the image)
.

Answer 1

Your first approach is probably the easiest one. But you should use the following overload instead: img.Composite(imgText, Gravity.South, CompositeOperator.Over); The default is CompositeOperator.In and that is not what you should use to get the label as an overlay.

Answer 2

In ImageMagick, you cannot draw transparency for text or background on an opaque image. So you have to draw a colored (black) rectangle, then flood fill it with transparency, then draw your colored text onto the transparent image. For example with your image:
convert image.png \
-draw "translate 250,250 fill black rectangle -50,-50 50,50 \
fill none matte 0,0 floodfill" \
-fill "rgba(255,0,0,1)" -pointsize 20 \
-gravity center -annotate +0+0 "TESTING" \
result.png
ADDITION:
If you only want the text, then leave out the background color and just write the text.
convert image.png \
-fill "red" -pointsize 20 \
-gravity center -annotate +0+0 "TESTING" \
result.png