I need to convert bitonal (black and white) TIFF files into another format for display by a web browser, currently we're using JPGs, but the format isn't crucial. From reading around .NET doesn't seem to easily support writing bitonal images, so we're ending up with ~1MB files instead of ~100K ones. I'm considering using ImageMagick to do this, but ideally i'd like a solution which doesn't require this if possible.
Current code snippet (which also does some resizing on the image):
using (Image img = Image.FromFile(imageName))
{
using (Bitmap resized = new Bitmap(resizedWidth, resizedHeight)
{
using (Graphics g = Graphics.FromImage(resized))
{
g.DrawImage(img, new Rectangle(0, 0, resized.Width, resized.Height), 0, 0, img.Width, img.Height, GraphicsUnit.Pixel);
}
resized.Save(outputFilename, System.Drawing.Imaging.ImageFormat.Jpeg);
}
}
Is there any way to achieve this?
Thanks.
I believe the problem can be solved by checking that resized bitmap is of PixelFormat.Format1bppIndexed. If it's not, you should convert it to 1bpp bitmap and after that you can save it as black and white png without problems.
In other words, you should use following code instead of resized.Save(outputFilename, System.Drawing.Imaging.ImageFormat.Jpeg);
if (resized.PixelFormat != PixelFormat.Format1bppIndexed)
{
using (Bitmap bmp = convertToBitonal(resized))
bmp.Save(outputFilename, System.Drawing.Imaging.ImageFormat.Png);
}
else
{
resized.Save(outputFilename, System.Drawing.Imaging.ImageFormat.Png);
}
I use following code for convertToBitonal :
private static Bitmap convertToBitonal(Bitmap original)
{
int sourceStride;
byte[] sourceBuffer = extractBytes(original, out sourceStride);
// Create destination bitmap
Bitmap destination = new Bitmap(original.Width, original.Height,
PixelFormat.Format1bppIndexed);
destination.SetResolution(original.HorizontalResolution, original.VerticalResolution);
// Lock destination bitmap in memory
BitmapData destinationData = destination.LockBits(
new Rectangle(0, 0, destination.Width, destination.Height),
ImageLockMode.WriteOnly, PixelFormat.Format1bppIndexed);
// Create buffer for destination bitmap bits
int imageSize = destinationData.Stride * destinationData.Height;
byte[] destinationBuffer = new byte[imageSize];
int sourceIndex = 0;
int destinationIndex = 0;
int pixelTotal = 0;
byte destinationValue = 0;
int pixelValue = 128;
int height = destination.Height;
int width = destination.Width;
int threshold = 500;
for (int y = 0; y < height; y++)
{
sourceIndex = y * sourceStride;
destinationIndex = y * destinationData.Stride;
destinationValue = 0;
pixelValue = 128;
for (int x = 0; x < width; x++)
{
// Compute pixel brightness (i.e. total of Red, Green, and Blue values)
pixelTotal = sourceBuffer[sourceIndex + 1] + sourceBuffer[sourceIndex + 2] +
sourceBuffer[sourceIndex + 3];
if (pixelTotal > threshold)
destinationValue += (byte)pixelValue;
if (pixelValue == 1)
{
destinationBuffer[destinationIndex] = destinationValue;
destinationIndex++;
destinationValue = 0;
pixelValue = 128;
}
else
{
pixelValue >>= 1;
}
sourceIndex += 4;
}
if (pixelValue != 128)
destinationBuffer[destinationIndex] = destinationValue;
}
Marshal.Copy(destinationBuffer, 0, destinationData.Scan0, imageSize);
destination.UnlockBits(destinationData);
return destination;
}
private static byte[] extractBytes(Bitmap original, out int stride)
{
Bitmap source = null;
try
{
// If original bitmap is not already in 32 BPP, ARGB format, then convert
if (original.PixelFormat != PixelFormat.Format32bppArgb)
{
source = new Bitmap(original.Width, original.Height, PixelFormat.Format32bppArgb);
source.SetResolution(original.HorizontalResolution, original.VerticalResolution);
using (Graphics g = Graphics.FromImage(source))
{
g.DrawImageUnscaled(original, 0, 0);
}
}
else
{
source = original;
}
// Lock source bitmap in memory
BitmapData sourceData = source.LockBits(
new Rectangle(0, 0, source.Width, source.Height),
ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
// Copy image data to binary array
int imageSize = sourceData.Stride * sourceData.Height;
byte[] sourceBuffer = new byte[imageSize];
Marshal.Copy(sourceData.Scan0, sourceBuffer, 0, imageSize);
// Unlock source bitmap
source.UnlockBits(sourceData);
stride = sourceData.Stride;
return sourceBuffer;
}
finally
{
if (source != original)
source.Dispose();
}
}
Have you tried saving using the Image.Save overload with Encoder parameters?
Like the Encoder.ColorDepth Parameter?
Trying jaroslav's suggestion for color depth doesn't work:
static void Main(string[] args)
{
var list = ImageCodecInfo.GetImageDecoders();
var jpegEncoder = list[1]; // i know this is the jpeg encoder by inspection
Bitmap bitmap = new Bitmap(500, 500);
Graphics g = Graphics.FromImage(bitmap);
g.DrawRectangle(new Pen(Color.Red), 10, 10, 300, 300);
var encoderParams = new EncoderParameters();
encoderParams.Param[0] = new EncoderParameter(Encoder.ColorDepth, 2);
bitmap.Save(@"c:\newbitmap.jpeg", jpegEncoder, encoderParams);
}
The jpeg is still a full color jpeg.
I don't think there is any support for grayscale jpeg in gdi plus. Have you tried looking in windows imaging component?
code example: http://www.codeproject.com/KB/GDI-plus/windows_imaging.aspx
wikipedia: http://en.wikipedia.org/wiki/Windows_Imaging_Component
Have you tried PNG with 1 bit color depth?
To achieve a size similar to a CCITT4 TIFF, I believe your image needs to use a 1-bit indexed pallette.
However, you can't use the Graphics object in .NET to draw on an indexed image.
You will probably have to use LockBits to manipulate each pixel.
This is an old thread. However, I'll add my 2 cents.
I use AForge.Net libraries (open source)
use these dlls. Aforge.dll, AForge.Imaging.dll
using AForge.Imaging.Filters;
private void ConvertBitmap()
{
markedBitmap = Grayscale.CommonAlgorithms.RMY.Apply(markedBitmap);
ApplyFilter(new FloydSteinbergDithering());
}
private void ApplyFilter(IFilter filter)
{
// apply filter
convertedBitmap = filter.Apply(markedBitmap);
}
来源：https://stackoverflow.com/questions/3414072/convert-bitonal-tiff-to-bitonal-png-in-c-sharp