Develop Reference

Bitmap image - Decrease the number of pixels

I am using the following code
Bitmap bitmap = new Bitmap(Screen.PrimaryScreen.Bounds.Width,Screen.PrimaryScreen.Bounds.Height);
Graphics graphics = Graphics.FromImage(bitmap as Image);
graphics.CopyFromScreen(0, 0, 0, 0, bitmap.Size);
bitmap.Save(#"C:\test\2560.png", ImageFormat.Png);
The code works. I take a screenshot of the screen with graphics.CopyFromScreen() and save the bitmap with bitmap.Save().
The image consists of 2560x1440 pixels. Basically I want to step through the pixels looking for a color value.
3,686,400 queries is too much for me and I would like to reduce the number of pixels, which means the image quality will deteriorate. Is there a possibility of
Image processing to reduce the number of pixels? So that some pixels blur together and result in an average value?
I set it with bitmap.SetResolution(800, 600); but unfortunately it didn't work.

This should do the trick.
Bitmap bitmap = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
Graphics graphics = Graphics.FromImage(bitmap as Image);
graphics.CopyFromScreen(0, 0, 0, 0, bitmap.Size);
Bitmap smallBmp = new Bitmap(bitmap, new Size(800, 600));
smallBmp.Save(#"C:\test\2560.png", ImageFormat.Png);

split image to multiple image from the bottom up

I have a picture I want to print, but it's too big for one page
so i have decided to split it into multiple images
i have tried a method, but now im using this (Talha Irfan answer)
i also tried the other solutions there but those didnt worked as well
(ex. bm.Clone(rec, bm.PixelFormat);)
and here's my code(this is on non-form class)
Bitmap bm = new Bitmap(frmPrint.Width, frmPrint.Height);
Rectangle rec = new Rectangle(0, 200, 576, 300);
Bitmap bitmap = cropImg(bm, rec);
frmPrint.DrawToBitmap(bitmap, rec);
frmPrint._img = bitmap;
frmPrint.setImage();
and setImage function(on some form)
public void setImage()
{
pictureBox3.BackgroundImage = _img;
this.ShowDialog();
}
and cropImg is the same as cropAtRect
the below shows the original image (on the left)
the wanted result in the blue rectangle
and the actual result on the right
PS
my actual image size is (height = 698, wifht = 576)
Edit - as suggested below
on non-form class
Rectangle cropRect = new Rectangle(0, 0, 576, 698);
Bitmap target = new Bitmap(cropRect.Width, cropRect.Height, bm.PixelFormat);
frmPrint.setImage(bm, target, cropRect);
target.Dispose();
at form class
public void setImage(Bitmap src, Bitmap target, Rectangle cropRect)
{
pictureBox3.Visible = false;
using (Graphics g = Graphics.FromImage(target))
{
g.DrawImage(src, new Rectangle(pictureBox3.Location.X, pictureBox3.Location.Y, target.Width, target.Height),
cropRect,
GraphicsUnit.Pixel);
}
this.ShowDialog();
}

Control.DrawToBitmap will always try to draw the whole control or form and will always start at the top. The parameter:
targetBounds
Type: System.Drawing.Rectangle
The bounds within which the control is rendered.
as the name implies, sets the target, not the source rectangle. Hence the white space above your result.
Move the line before cropping with a rectangle that holds the full area, maybe like this:
DrawToBitmap(bm, ClientRectangle);
and then crop the lower part as before..
Note that the cropping trick from your link will not work for DrawToBitmap; using a rectangle with a negative offset will cause a parameter exception.
Btw: to safely dispose of a Bitmap in a PictureBox use this:
Bitmap dummy = (Bitmap )somePictureBox.Image;
somePictureBox.Image = null;
if (dummy != null) dummy.Dispose;
And, indeed, the answer by ChrisJJ in the link leaks the Graphics object.
Update:
Since you seem to have lost control over the various changes and suggestions, here is the minimal code change from the original post:
Bitmap bm = new Bitmap(frmPrint.ClientWidth, frmPrint.ClientHeight);
DrawToBitmap(bm, frmPrint.ClientRectangle);
Rectangle rec = new Rectangle(0, 200, 576, 300);
Bitmap bitmap = cropImg(bm, rec);
frmPrint._img = bitmap;
frmPrint.setImage();
With:
public void setImage()
{
Bitmap dummy = pictureBox3.BackgroundImage;
pictureBox3.BackgroundImage = null;
if (dummy != bnull) dummy.Dispose();
pictureBox3.BackgroundImage = _img;
this.ShowDialog();
}
In the cropImg function add a g.Dispose before returning.

Converting a image to 32bpp format gives strange offset?

I have the following code:
public static Bitmap ConvertTo32bppArgb(this Image image)
{
Bitmap newBmp = new Bitmap(image.Width, image.Height, PixelFormat.Format32bppArgb);
using (Graphics gfx = Graphics.FromImage(newBmp))
{
gfx.PixelOffsetMode = PixelOffsetMode.HighQuality;
gfx.InterpolationMode = InterpolationMode.NearestNeighbor;
gfx.DrawImage(image, 0, 0);
}
return newBmp;
}
However with some images this is giving some weird 1 pixel offset in that starts somewhere in the middle of the image. This happens with Format32bppArgb format but not with Format8bppIndexed.
What i want is that this function always returns a Bitmap that has Format32bppArgb (without that strange offset ofcourse).
Original image:
Processed image (see the tile 7th tile from the top (starts at pixel coordinates 0, 192) its 32x33 instead of 32x32)):

Generated Bitmap Displays Weirdly in PictureBox

I cannot seem to programmatically create a colored bitmap to display in a PictureBox. The bitmap saves normally as a file, but is faded at the edges when displayed in a PictureBox. Here is simplified code used to create and display the Bitmap (in actual code, the bitmap generation is completely separate from the form, so forcing the bitmap size to match the picturebox size isn't possible):
Bitmap Bmp = new Bitmap(4, 4, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
using (Graphics gfx = Graphics.FromImage(Bmp))
using (SolidBrush brush = new SolidBrush(Color.BlueViolet))
{
gfx.FillRectangle(brush, 0, 0, 4, 4);
}
Then set the Image value on a PictureBox to the generated Bitmap:
pictureBox1.Image = Bmp;
Here is the resulting bitmap displayed in a 300x300 picturebox:
How do I set the Image on the PictureBox so that it displays the colored bitmap properly (full solid)?
EDIT: I am restricted to generating smaller source bitmaps, so upscaling into a PictureBox is unavoidable. The problem appears when the generated source bitmap is 4px or 100px square, so I believe these are relevant cases.
EDIT: The PictureBox scaling should be set to stretch or zoom for the issue to manifest. In this example case the 4x4 source bitmap is stretched to 300x300.
EDIT: The basic problem is PictureBox's inability to upscale small bitmaps into large controls. This is confusing because the Bitmap upscales nicely into a PictureBox.Background image. Unless you have a magic bullet that will fix the image upscaling problem, I think it might be best to go for clear and simple workarounds in your answer.

You are generating a 4x4 bitmap and it's being stretched. Specify the size to match the picture box instead:
int width = pictureBox1.Width;
int height = pictureBox1.Height;
var Bmp = new Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
using (Graphics gfx = Graphics.FromImage(Bmp))
using (var brush = new SolidBrush(Color.BlueViolet))
{
gfx.FillRectangle(brush, 0, 0, width, height);
}
pictureBox1.Image = Bmp;

You will need to turn anti-aliasing off. Also, since you are using one color for the whole picturebox, why not make the bitmap 1x1? If you need it 4x4, change the int the top of the example from 1 to 4.
int hw = 1;
Bitmap Bmp = new Bitmap(hw, hw,
System.Drawing.Imaging.PixelFormat.Format24bppRgb);
using (Graphics gfx = Graphics.FromImage(Bmp))
{
// Turn off anti-aliasing and draw an exact copy
gfx.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.None;
gfx.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy;
using (SolidBrush brush = new SolidBrush(Color.BlueViolet))
{
gfx.FillRectangle(brush, 0, 0, hw, hw);
}
}
pictureBox1.Image = Bmp;
UPDATE
Since you are still having the same issue by setting the picturebox to the image, you will have to get the graphics object from the picturebox and draw directly on it.
The code is very similar.
using (Graphics gfx = Graphics.FromImage(pictureBox1.Image))
{
// Turn off anti-aliasing and draw an exact copy
gfx.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.None;
gfx.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy;
using (SolidBrush brush = new SolidBrush(Color.BlueViolet))
{
gfx.FillRectangle(brush, 0, 0,
pictureBox11.Width - 1,
pictureBox11.Height - 1);
}
}
// Force the picturebox to redraw with the new image.
// You could also use pictureBox11.Refresh() to do the redraw.
pictureBox11.Invalidate();

I tried to test your code and the image were properly displayed.
But when i used this code:
Rectangle srcRect = New Rectangle(0, 0, Bmp.Width, Bmp.Height);
Rectangle dstRect = New Rectangle(0, 0, PictureBox1.Width, PictureBox1.Height);
g = PictureBox1.CreateGraphics;
g.DrawImage(Bmp, dstRect, srcRect, GraphicsUnit.Pixel);
g.Dispose();
I did get exactly your result. In order to fix it:
Rectangle srcRect = New Rectangle(0, 0, Bmp.Width - 1, Bmp.Height - 1);
Rectangle dstRect = New Rectangle(0, 0, PictureBox1.Width, PictureBox1.Height);
g = PictureBox1.CreateGraphics;
g.DrawImage(Bmp, dstRect, srcRect, GraphicsUnit.Pixel);
g.Dispose();
Edit:
So you have the bitmap and you want to stretch it. And the bitmap has ane solid color. Do this insted:
Color pixelColor = Bmp.GetPixel(0, 0);
PictureBox1.BackColor = pixelColor;
valter

Save non-transparent image from a PictureBox with transparent images

I have a PictureBox with lots of transparent png's drawn into...
Now I'd like to save the content of this PictureBox to a file, but without the transparency.
How can I do this?
I have already tried to remove transparency from the Image like this, but it didn't work, I still got a transparent image after the save.
...
removeTransparency(pictureBox.Image).Save(saveFileDialog.FileName);
private Bitmap removeTransparency(Image transparentImage)
{
Bitmap src = new Bitmap(transparentImage);
Bitmap newImage = new Bitmap(src.Size.Width, src.Size.Height);
Graphics g = Graphics.FromImage(newImage);
g.DrawRectangle(new Pen(new SolidBrush(Color.White)), 0, 0, newImage.Width, newImage.Height);
g.DrawImage(src, 0, 0);
return newImage;
}

You may cycle through all pixel (please not using GetPixel/SetPixel) to change the color or you may create another bitmap with the same size, create a graphics context from the image, clear the image with your favorite background color and then draw your image on it (so transparent pixels simply will be replaced by the background color).
Example
Did you do something like this?
public static Bitmap Repaint(Bitmap source, Color backgroundColor)
{
Bitmap result = new Bitmap(source.Width, source.Height, PixelFormat.Format32bppArgb);
using (Graphics g = Graphics.FromImage(result))
{
g.Clear(backgroundColor);
g.DrawImage(source, new Rectangle(0, 0, source.Width, source.Height));
}
return result;
}