Develop Reference

How to make a listBox semi-transparent?

I tried looking through a few questions on here already but none seemed to fit.
This is what i've tried:
listBox1.BackColor = Color.FromArgb(85, 200, 200, 200);
But at runtime, there's an error. It states that the component doesn't support transparency. I'm asking on here because there could be a workaround. If anyone could help, that'd be great. Thanks in advance!

I suggest going for a ListView in Details View instead.
This is a more modern control, much more powerful and also more supportive when it comes to adding some extra styling..
ListView has a BackgroundImage which alone may be good enough. It doesn't support transparency, though.
But with a few tricks you can make it fake it by copying the background that would shine through..:
void setLVBack(ListView lv)
{
int alpha = 64;
Point p1 = lv.Parent.PointToScreen(lv.Location);
Point p2 = lv.PointToScreen(Point.Empty);
p2.Offset(-p1.X, -p1.Y );
if (lv.BackgroundImage != null) lv.BackgroundImage.Dispose();
lv.Hide();
Bitmap bmp = new Bitmap(lv.Parent.Width, lv.Parent.Height);
lv.Parent.DrawToBitmap(bmp, lv.Parent.ClientRectangle);
Rectangle r = lv.Bounds;
r.Offset(p2.X, p2.Y);
bmp = bmp.Clone(r, PixelFormat.Format32bppArgb);
using (Graphics g = Graphics.FromImage(bmp))
using (SolidBrush br = new SolidBrush(Color.FromArgb(alpha, lv.BackColor)))
{
g.FillRectangle(br, lv.ClientRectangle);
}
lv.BackgroundImage = bmp;
lv.Show();
}
A few notes:
I hide the listview for a short moment while getting the background pixels
I calculate an offset to allow borders; one could (and maybe should?) also use SystemInformation.Border3DSize.Height etc..
I crop the right area using a bitmap.Clone overload
finally I paint over the image with the background color of the LV, green in my case
you can set the alpha to control how much I paint over the image
Also note that I dispose of any previous image, so you can repeat the call when necessary, e.g. when sizes or positions change or the background etc..
The ListView overlaps a PictureBox (left) but sits on a TabPage with an image of its own.
Result:

Invert Crop from (Cut hole into) Image

Everywhere I look online, I see people posting on how to successfully crop an image. However, I want to 'crop'/ clear a hole out of an image. I want to keep the original image, but crop out a rectangle
As you can see in the image above, I have "cropped" out the kittens face. I maintained the original image, but removed only part of it. I cannot figure out how to do that.

Assuming you want to replace the original pixel colors with transparency you run into a small problem: You can't draw or fill with transparency in GDI+.
But you can use Graphics.Clear(Color.Transparent).
To do that you restrict the region where the Graphics object will draw. Here we can use the simple cropping rectangle but you can clear more complex shapes using a GraphicsPath..
Example using a bitmap bmp:
using (Graphics g = Graphics.FromImage(bmp))
{
Rectangle crop = new Rectangle(222,222,55,55);
g.SetClip(crop);
g.Clear(Color.Transparent);
}
bmp.Save(somefilename, ImageFormat.Png);

Setting your Graphics object's CompositingMode property to CompositingMode.SourceCopy will allow your drawing operations to replace the alpha value instead of proportionally opacifying it:
public static void TestDrawTransparent()
{
//This code will, successfully, draw something transparent overwriting an opaque area.
//More precisely, it creates a 100*100 fully-opaque red square with a 50*50 semi-transparent center.
using(Bitmap bmp = new Bitmap(100, 100, PixelFormat.Format32bppArgb))
{
using(Graphics g = Graphics.FromImage(bmp))
using(Brush opaqueRedBrush = new SolidBrush(Color.FromArgb(255, 255, 0, 0)))
using(Brush semiRedBrush = new SolidBrush(Color.FromArgb(128, 255, 0, 0)))
{
g.Clear(Color.Transparent);
Rectangle bigRect = new Rectangle(0, 0, 100, 100);
Rectangle smallRect = new Rectangle(25, 25, 50, 50);
g.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy;
g.FillRectangle(opaqueRedBrush, bigRect);
g.FillRectangle(semiRedBrush, smallRect);
}
bmp.Save(#"C:\FilePath\TestDrawTransparent.png", ImageFormat.Png);
}
}
In this code, I first draw a fully-opaque red square, then a semi-transparent red square "over" it. The result is a semi-transparent "hole" in the square:
And on a black background:
A zero-opacity brush works just as well, leaving a clear hole through the image (I checked).
With that in mind, you should be able to crop any shapes you want, simply by filling them with a zero-opacity brush.

CSharp Windows Form Picturebox Draw Small Image Without Quality Loss

I'm trying to create a level editor using Windows Forms for my monogame project and need to draw small pixel based images to a picture box with no quality loss when scaled. In monogame when I need to do this I can just set the draw type to PointClamp and then each pixel is drawn as is instead of being pixelated when zoomed; I was hoping for something like this via a picturebox. Right now it looks like this But I'd prefer a more crisp and clean image like this (The second is how it'll appear in monogame). I haven't uploaded any code for this, but just assume I grabbed an image from the filestream and used the bitmap constructor to scale it up (don't think that's relevent but I'll just put it out there).
Image croppedImage, image = tileMap.tileBox.Image;
var brush = new SolidBrush(Color.Black);
try { croppedImage = CropImage(image, tileMap.highlightedRect); } catch {
return; // If crop target is outside bounds of image then return
}
float scale = Math.Min(higlightedTileBox.Width / croppedImage.Width, higlightedTileBox.Height / image.Height);
var scaleWidth = (int)(higlightedTileBox.Width * scale);
var scaleHeight = (int)(higlightedTileBox.Height * scale);
try { higlightedTileBox.Image = new Bitmap(croppedImage, new Size(scaleWidth, scaleHeight)); } catch {
return; // Image couldn't be scaled or highlighted tileBox couldn't be set to desired image
}
CropImage:
private static Image CropImage(Bitmap img, Rectangle cropArea) {
return img.Clone(cropArea, img.PixelFormat);
}
private static Image CropImage(Image img, Rectangle cropArea) {
return CropImage(new Bitmap(img), cropArea);
}
The code above is my current method in it's entirety. tileMap is a form and tilebox is the picturebox within that form.image is the full spritesheet texture before being cropped to what the user has highlighted. After being cropped I attempt to set the current picturebox (highlightedTileBox's) image to a scaled up version of the cropped image.

So I got a solution by trying around a bit.
It looks like scaling images directly by size is using some sort of interpolation.
To try different interpolation modes supported by Winforms, I created a little demo.
As you can see, every label contains the name of the InterpolationMode and is followed by its resulting image. The original bitmap I used is the small one at the top.
From your question, it looks like you would like to achieve something like NearestNeighbour.
Following code scales bmp and the result is stored in bmp2. Try if that's what you want. Consider building a proper implementation if you're using this as solution (disposing unused bitmaps etc.).
I hope it helps.
Bitmap bmp = new Bitmap("test.bmp");
Bitmap bmp2;
Graphics g = Graphics.FromImage(bmp2=new Bitmap(bmp.Width * 2, bmp.Height * 2));
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.NearestNeighbor;
g.DrawImage(bmp, 0, 0, bmp.Width * 2, bmp.Height * 2);
g.Dispose();

Remove the black background color of a bitmap

I need to remove the black background color of a bitmap in C# VS2013.
It is just like that I draw some points on a canvas. The canvas is black and I just need to change the canvas to be transparent meanwhile keeping colorful points on it without any changes.
I got the solution at:
How to remove white background color from Bitmap
Bitmap capcha = new Bitmap(#"C:/image.png");
capcha.MakeTransparent(Color.Black);
But, the background still have a gray color like a fog covering the points on the image.
How to remove it ?
UPDATE
I used the code:
ImageAttribute imageAttribute = new ImageAttribute();
imageAttribute.SetGamma(0.5f, ColorAdjustType.Bitmap);
gr.DrawImage(img, new Rectangle(0, 0, img.Width, img.Height),
0, 0, img.Width, img.Height, GraphicsUnit.Pixel, imageAttribute );
I got same thing.
More update of C# code to draw an image :
System.Drawing.Bitmap canvasImage = new System.Drawing.Bitmap(xSize, ySize, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
canvasImage.MakeTransparent(Color.Black);
Graphics g = Graphics.FromImage(canvasImage);
System.Drawing.Bitmap tempImage = myDrawImageFunction(myPoints);
g.Clear(Color.Transparent); // this only give me an empty image without any points on it. But, if I uncomment it, I will have an image with black background.
// my understanding about g.DrawImage() is to draw points on tempImage
// after clearing the background. But, the image still have a foggy covering on the image.
g.DrawImage(tempImage, new System.Drawing.PointF(x_position, y_position));
I want to have a transparent background for "tempImage" before any points are drawn on it.
The example image has a back ground that needs to be removed but the colorful points on the image need to be kept without any changes.

This will do the job:
public Color MakeTransparent(Color c, int threshold)
{ // calculate the weighed brightness:
byte val = (byte)((c.R * 0.299f + c.G * 0.587f + c.B * 0.114f));
return val < threshold ? Color.FromArgb(0, c.R, c.G, c.B) : c;
}
You could use it in a double loop over the pixels, but for fast results you should call it from the code in this post (second part!) which uses LockBits.
Change this
ModifyHue hueChanger = new ModifyHue(MaxChannel);
to the new function:
ModifyHue hueChanger = new ModifyHue(MakeTransparent);
and call it with a suitable threshold, maybe 10 or 20..:
c = hueChanger(c, 20);
The function skips the call to the system's MakeTransparent function and directly sets the alpha channel of each pixel to 0.
If you want to create a uniform color instead of a transparent one it should be easy to modify (e.g. by returning Color.FromArgb(255, 0, 0, 0) for solid black)
Do note that, while the code in the linked post takes both 24 and 32 bbp formats you should definitely not save as JPG, as this will re-introduce artifacts and the result will not work well with e.g. a TransparencyKey color..
Instead do save it as PNG, as Hans suggests!
I hope you can modify the button code to a function :-)

TextRenderer.DrawText in Bitmap vs OnPaintBackground

If I use TextRenderer.DrawText() using the Graphics object provided in the OnPaintBackground my text looks perfect. If I create my own Bitmap and use the Graphics object obtained from my Bitmap my text looks terrible. It looks like it is anti-aliasing the text using black, not the bitmap's background color. I can avoid this problem if I use Graphics.DrawString(), but this method has horrible kerning problems. What should I do? How can I get TextRenderer.DrawText() to anti-alias properly using the Bitmap's contents?
Looks terrible:
Bitmap bmp = new Bitmap(100, 100, PixelFormat.Format32bppArgb);
using (Graphics g = Graphics.FromImage(bmp))
{
g.Clear(Color.Red);
TextFormatFlags tf = TextFormatFlags.Left;
TextRenderer.DrawText(g, #"C:\Development\Testing\blag", font, clip, Color.White,
Color.Transparent, tf);
}
Looks good, but I want to render this onto a bitmap, NOT onto the control's surface:
protected override void OnPaintBackground(PaintEventArgs e)
{
e.Graphics.Clear(Color.Red);
TextFormatFlags tf = TextFormatFlags.Left;
TextRenderer.DrawText(e.Graphics, #"C:\Development\Testing\blag", font, clip,
Color.White, Color.Transparent, tf);
}
What is the difference?

The answer is not to use TextRenderer. TextRenderer is a wrapper for the GDI (not GDI+) implementation of text rendering, which has lots of features, but doesn't interoperate well with in-memory DCs as you have discovered.
Use Graphics.DrawString & Graphics.MeasureString, but remember to pass it StringFormat.GenericTypographic to get accurate size and positioning.
The reason TextRenderer was introduced initially was that GDI+ didn't support all the complex scripts that GDI's Uniscribe engine did. Over time however GDI+ support for complex scripts has been expanded, and these days there aren't any good reasons left to use TextRenderer (it's not even the faster of the two anymore, in fact quite the opposite it appears).
Really, though, unless you are running into serious, measurable performance issues just use Graphics.DrawString.

I believe the problem is that the clear type text rendering doesn't work if the background is transparent. A few possible solutions.
Option 1. Fill the background of your bitmap with a color.
If you do this (as Tim Robinson did above in his code example by using g.Clear(Color.Red)) clear type will do the right thing. But your bitmap won't be completely transparent which might not be acceptable. If you use Graphics.MeasureText, you can fill just the rectangle around your text, if you like.
Option 2. Set TextRenderingHint = TextRenderingHintAntiAliasGridFit
This appears to turn off clear type. The text will be rendered at a lower quality than clear type on a background, but much better than the mess clear type on no background creates.
Option 3. Fill the text rectangle with white, draw the text and then find all the non-text pixels and put them back to transparent.
using (Bitmap bmp = new Bitmap(someWidth, someHeight))
{
using (Graphics g = Graphics.FromImage(bmp))
{
// figure out where our text will go
Point textPoint = new Point(someX, someY);
Size textSize = g.MeasureString(someText, someFont).ToSize();
Rectangle textRect = new Rectangle(textPoint, textSize);
// fill that rect with white
g.FillRectangle(Brushes.White, textRect);
// draw the text
g.DrawString(someText, someFont, Brushes.Black, textPoint);
// set any pure white pixels back to transparent
for (int x = textRect.Left; x <= textRect.Left + textRect.Width; x++)
{
for (int y = textRect.Top; y <= textRect.Top + textRect.Height; y++)
{
Color c = bmp.GetPixel(x, y);
if (c.A == 255 && c.R == 255 && c.G == 255 && c.B == 255)
{
bmp.SetPixel(x, y, Color.Transparent);
}
}
}
}
}
I know, it's a horrible hack, but it appears to work.

The answer is to use a BuffersGraphicsContext. This is the same system that .NET uses internally when you set the ControlStyles.OptimizedDoubleBuffer style on a control.
See http://msdn.microsoft.com/en-us/library/b367a457.aspx for more information about double buffering in .NET.

Another possible solution: Draw the whole thing to the screen, bitmap with text on top, and then write some code to 'screen capture' that portion of the screen. Not practical in all cases but you're right, DrawString creates weird text and DrawText onto a bitmap looks horrible.

If your bitmap is not the same size as your display area, it might just be a resizing issue, where .NET scales the bitmap to the display size and you get funny looking text.
Can you test with a bitmap created at the same size as your display area?

Can you post the smallest program that suffers from this problem? I can't reproduce it like this -- the antialiasing looks fine:
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;
public class Program
{
public static void Main()
{
Bitmap bmp = new Bitmap(100, 100, PixelFormat.Format32bppArgb);
using (Font font = new Font("Arial", 10, GraphicsUnit.Point))
using (Graphics g = Graphics.FromImage(bmp))
{
Rectangle clip = Rectangle.FromLTRB(0, 0, 100, 100);
g.Clear(Color.Red);
TextFormatFlags tf = TextFormatFlags.Left;
TextRenderer.DrawText(g, #"C:\Development\Testing\blag", font, clip, Color.White, Color.Transparent, tf);
}
Form form = new Form();
form.BackgroundImage = bmp;
Application.Run(form);
}
}