Develop Reference

C# how to compress .png without transparent background lost?

I use the following codes to compress an image file to jpg:
// _rawBitmap = a Bitmap object
ImageCodecInfo encoder = GetEncoder(ImageFormat.Jpeg);
System.Drawing.Imaging.Encoder myEncoder = System.Drawing.Imaging.Encoder.Quality;
EncoderParameters myEncoderParameters = new EncoderParameters(1);
EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 50L);
myEncoderParameters.Param[0] = myEncoderParameter;
ImageConverter imageConverter = new ImageConverter();
byte[] b = (byte[])imageConverter.ConvertTo(_rawBitmap, typeof(byte[]));
using (MemoryStream ms = new MemoryStream())
{
ms.Write(b, 0, b.Length);
ms.Seek(0, SeekOrigin.Begin);
rawBitmap.Save(ms, encoder, myEncoderParameters);
bmp = ToBitmap(ms.ToArray());
return (Bitmap)bmp.Clone();
}
but when I try to compress a png file with same way but only change:
ImageCodecInfo encoder = GetEncoder(ImageFormat.Jpeg);
to
ImageCodecInfo encoder = GetEncoder(ImageFormat.Png);
my png file lost transparent data.
so how to compress a PNG file properly?

There are a couple of problems here.
First, you don't need to set those EncoderParams for quality for PNG.
Second, you don't need ImageConverter
Third, you are writing whatever ImageConverter produces to your memory stream, rewinding, and then writing the encoded PNG over the top of it-- it is likely that you have a PNG file with a bunch of garbage at the end of it as a result.
The simplified approach should be:
using (MemoryStream ms = new MemoryStream())
{
rawBitmap.Save(ms, ImageFormat.Png);
}
If you want to load your bitmap back, open it from the stream, but don't close the stream (the stream will be disposed when your returned Bitmap is disposed):
var ms = new MemoryStream();
rawBitmap.Save(ms, ImageFormat.Png);
ms.Seek(0, SeekOrigin.Begin);
return Bitmap.FromStream(ms);

You can use nQuant (https://www.nuget.org/packages/nQuant/)
With it, you convert 32 bit PNGs to high quality 8 bit PNGs
private static int alphaTransparency = 10;
private static int alphaFader = 70;
var quantizer = new WuQuantizer();
using(var bitmap = new Bitmap(sourcePath))
{
using(var quantized = quantizer.QuantizeImage(bitmap, alphaTransparency, alphaFader))
{
quantized.Save(targetPath, ImageFormat.Png);
}
}

How to save image using JpegBitmapEncoder

According to the image encoding example here I should be able to use JpegBitmapEncoder to encode an image for saving as a jpeg file but get this compile error:
error CS1503: Argument 1: cannot convert from 'System.Windows.Controls.Image' to 'System.Uri'
I don't see a way (property or method in Image) to get System.Uri from Image.
What am I missing?
The Image xaml code is
<Image Name="ColorImage"/>
The SaveImage C# is
...
SaveImage(ColorImage, path);
...
private void SaveImage(Image image, string path)
{
var jpegEncoder = new JpegBitmapEncoder();
jpegEncoder.Frames.Add(BitmapFrame.Create(image));
using (var fs = new FileStream(path, FileMode.Create, FileAccess.Write))
{
jpegEncoder.Save(fs);
}
}
The code below (taken mostly from the kinect-sdk) streams 640 x 480 RBG to a WriteableBitmap at 30 Fps (the kinect ColorImageFormat is RgbResolution640x480Fps30).
using (var colorImageFrame = allFramesReadyEventArgs.OpenColorImageFrame())
{
if (colorImageFrame == null) return;
var haveNewFormat = currentColorImageFormat != colorImageFrame.Format;
if (haveNewFormat)
{
currentColorImageFormat = colorImageFrame.Format;
colorImageData = new byte[colorImageFrame.PixelDataLength];
colorImageWritableBitmap = new WriteableBitmap(
colorImageFrame.Width,
colorImageFrame.Height, 96, 96, PixelFormats.Bgr32, null);
ColorImage.Source = colorImageWritableBitmap;
}
// Make a copy of the color frame for displaying.
colorImageFrame.CopyPixelDataTo(colorImageData);
colorImageWritableBitmap.WritePixels(
new Int32Rect(0, 0, colorImageFrame.Width, colorImageFrame.Height),
colorImageData,
colorImageFrame.Width*Bgr32BytesPerPixel,
0);
}

private void SaveImage(string path)
{
var jpegEncoder = new JpegBitmapEncoder();
jpegEncoder.Frames.Add(BitmapFrame.Create(colorImageWritableBitmap));
using (var fs = new FileStream(path, FileMode.Create, FileAccess.Write))
{
jpegEncoder.Save(fs);
}
}

The problem occurs, because you pass an Image to BitmapFrame.Create. Imageis more common in Windows Forms. A simple approach would be to create a MemoryStream first and the pass this:
private void SaveImage(Image image, string path)
{
MemoryStream ms = new MemoryStream();
image.Save(ms,System.Drawing.Imaging.ImageFormat.Jpeg);
var jpegEncoder = new JpegBitmapEncoder();
jpegEncoder.Frames.Add(BitmapFrame.Create(ms));
using (var fs = new FileStream(path, FileMode.Create, FileAccess.Write))
{
jpegEncoder.Save(fs);
}
}
Addition (see conversation in comments):
you could try to use the CopyPixels method on the writeableBitmap object and copy the pixels to a byte array which you load to a MemoryStream and the write it to a Jpeg File withe the JpegBitmapEncoder. But it's just a guess.
This could work, too:
private void SaveImage (WriteableBitmap img, string path)
{
FileStream stream = new FileStream(path, FileMode.Create);
JpegBitmapEncoder encoder = new JpegBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(img));
encoder.Save(stream);
stream.Close();
}
You will just have to extract the WriteableBitmap from your Image control

Try: BitmapFrame.Create(image.Source)

Get all pictures and save it to file

I have a UniformGrid containing all my video thumbnails taken (they are all System.Windows.Control.Image). My goal here is to save a jpg of all the thumbnails after I click a button. Is there a way to grab a bitmap image or something from a UbiformGrid?
I am using C# with WPF.
Edit: like a screenshot. But I don't want to window border, only the grid content.
Edit2: I finally found a solution. Thanks for the help.
RenderTargetBitmap renderTarget = new RenderTargetBitmap((int)ThumbnailPanel.Width,
(int)ThumbnailPanel.Height, 96, 96, PixelFormats.Pbgra32);
VisualBrush sourceBrush = new VisualBrush(ThumbnailPanel);
DrawingVisual drawingVisual = new DrawingVisual();
DrawingContext drawingContext = drawingVisual.RenderOpen();
using (drawingContext)
{
drawingContext.DrawRectangle(sourceBrush, null, new Rect(new Point(0, 0), new Point(ThumbnailPanel.Width, ThumbnailPanel.Height)));
}
renderTarget.Render(drawingVisual);
JpegBitmapEncoder jpgEncoder = new JpegBitmapEncoder();
jpgEncoder.QualityLevel = 80;
jpgEncoder.Frames.Add(BitmapFrame.Create(renderTarget));
Byte[] _imageArray;
using (MemoryStream outputStream = new MemoryStream())
{
jpgEncoder.Save(outputStream);
_imageArray = outputStream.ToArray();
}
FileStream fileStream = new FileStream(#"myThumbnails.jpg", FileMode.Create, FileAccess.ReadWrite);
BinaryWriter binaryWriter = new BinaryWriter(fileStream);
binaryWriter.Write(_imageArray);
binaryWriter.Close();

Sure, just iterate through your collection of images with for or foreach and use the Image.GetThumbnailImage method from the System.Drawing namespace to create thumbnails... it's that simple.
For example:
foreach (var img in myImages)
{
var thumb = image.GetThumbnailImage(thumbnailSize.Width, thumbnailSize.Height, null, IntPtr.Zero);
//Do something with the thumbnail
thumb.Save(output)
}

Change TIFF palette from 8 bit into 32 bit

I have some set of TIFF files (8-bit palette). I need to change the bit depth into 32 bit.
I tried the code below, but getting an error, that the parameter is not correct... Could you help me to fix it? Or maybe some1 is able to suggest some different solution for my problem.
public static class TiffConverter
{
public static void Convert8To32Bit(string fileName)
{
BitmapSource bitmapSource;
using (Stream imageStreamSource = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read))
{
TiffBitmapDecoder decoder = new TiffBitmapDecoder(imageStreamSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
bitmapSource = decoder.Frames[0];
}
using (FileStream stream = new FileStream(fileName, FileMode.OpenOrCreate))
{
ImageCodecInfo tiffCodec = ImageCodecInfo.GetImageEncoders().FirstOrDefault(codec => codec.FormatID.Equals(ImageFormat.Tiff.Guid));
if (tiffCodec != null)
{
Image image = BitmapFromSource(bitmapSource);
EncoderParameters parameters = new EncoderParameters();
parameters.Param[0] = new EncoderParameter(Encoder.ColorDepth, 32);
image.Save(stream, tiffCodec, parameters);
}
}
}
private static Bitmap BitmapFromSource(BitmapSource bitmapSource)
{
Bitmap bitmap;
using (MemoryStream outStream = new MemoryStream())
{
BitmapEncoder enc = new BmpBitmapEncoder();
enc.Frames.Add(BitmapFrame.Create(bitmapSource));
enc.Save(outStream);
bitmap = new Bitmap(outStream);
}
return bitmap;
}
}
Thanks in advance!
[edit]
I noticed that the error appears in this line:
image.Save(stream, tiffCodec, parameters);
ArgumentException occured: Parameter is not valid.

If the error you're getting is on the line:
parameters.Param[0] = new EncoderParameter(Encoder.ColorDepth, 32);
then the problem is that the compiler cannot know if you're referring System.Text.Encoder or System.Drawing.Imaging.Encoder...
Your code should look like this to to avoid any ambiguity:
parameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.ColorDepth, 32);
Edit:
This is an alternative (and tested :)) way of doing the same thing:
Image inputImg = Image.FromFile("input.tif");
var outputImg = new Bitmap(inputImg.Width, inputImg.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
using (var gr = Graphics.FromImage(outputImg))
gr.DrawImage(inputImg, new Rectangle(0, 0, inputImg.Width, inputImg.Height));
outputImg.Save("output.tif", ImageFormat.Tiff);

Set background color in Bitmap Image

I want to save my canvas to image. It works but background color is black. How I must add to change the color?
I use this code:
Size size = new Size(surface.Width, surface.Height);
surface.Measure(size);
surface.Arrange(new Rect(size));
// Create a render bitmap and push the surface to it
RenderTargetBitmap renderBitmap =
new RenderTargetBitmap((int)size.Width, (int)size.Height, 96d, 96d,
PixelFormats.Pbgra32);
renderBitmap.Render(surface);
// Create a file stream for saving image
using (FileStream outStream = new FileStream(filename, FileMode.Create))
{
BmpBitmapEncoder encoder = new BmpBitmapEncoder();
// push the rendered bitmap to it
encoder.Frames.Add(BitmapFrame.Create(renderBitmap));
// save the data to the stream
encoder.Save(outStream);
}

Try this
Size size = new Size(surface.Width, surface.Height);
surface.Measure(size);
surface.Arrange(new Rect(size));
// Create a render bitmap and push the surface to it
RenderTargetBitmap renderBitmap =
new RenderTargetBitmap((int)size.Width, (int)size.Height, 96d, 96d,
PixelFormats.Pbgra32);
DrawingVisual drawingVisual = new DrawingVisual();
using (DrawingContext drawingContext = drawingVisual.RenderOpen())
{
VisualBrush visualBrush = new VisualBrush(surface);
drawingContext.DrawRectangle(visualBrush, null,
new Rect(new Point(), new Size(size.Width, size.Height)));
}
renderBitmap.Render(drawingVisual);
// Create a file stream for saving image
using (FileStream outStream = new FileStream(filename, FileMode.Create))
{
BmpBitmapEncoder encoder = new BmpBitmapEncoder();
// push the rendered bitmap to it
encoder.Frames.Add(BitmapFrame.Create(renderBitmap));
// save the data to the stream
encoder.Save(outStream);
}

Try PixelFormats.Default or PixelFormats.Bgra32 or PixelFormats.Rgb24 instead of PixelFormats.Pbgra32.
The P stands for pre-multiplied - the assumption is that each channel is pre-multiplied by alpha.
MSDN reference