Simple posterization of an image.
The class implements simple posterization of an image by splitting each color plane into adjacent areas of the
Posterization is a process in photograph development which converts normal photographs into an image consisting of distinct, but flat, areas of different tones or colors.
The filter accepts 8 bpp grayscale and 24/32 bpp color images.
Sample usage:
// create filter SimplePosterization filter = new SimplePosterization( ); // process image filter.ApplyInPlace( sourceImage ); Initial image:
Result image:
private Bitmap preProcessImage(Bitmap image, Grayscale gScale, SobelEdgeDetector sEgDetector, SimplePosterization posterization)
{
Bitmap temp = image;
temp = gScale.Apply(temp);
posterization.ApplyInPlace(temp);
return temp;
}
protected void ApplyFiltersTo(ref Bitmap b, ImageState s)
{
//TODO: if the image is unrotated, use a rectangle to limit the effect to the desired area
string str = null;
int i = 0;
//If radiusunits is specified, use that code path.
double units = s.settings.Get<double>("a.radiusunits",1000);
i = GetRadius(s, "blur", "a.blur", units);
if (i > 0) new GaussianBlur(1.4, i).ApplyInPlace(b);
i = GetRadius(s, "sharpen", "a.sharpen", units);
if (i > 0) new GaussianSharpen(1.4, Math.Min(11,i)).ApplyInPlace(b);
i = GetRadius(s, "a.oilpainting", null, units);
if (i > 0) new OilPainting(i).ApplyInPlace(b);
if ("true".Equals(s.settings["a.removenoise"], StringComparison.OrdinalIgnoreCase)) {
new ConservativeSmoothing(3).ApplyInPlace(b);
} else {
i = GetRadius(s, "a.removenoise", null, units);
if (i > 0) new ConservativeSmoothing(i).ApplyInPlace(b);
}
//Sobel only supports 8bpp grayscale images.
//true/false
if ("true".Equals(s.settings["a.sobel"], StringComparison.OrdinalIgnoreCase)){
Bitmap old = b;
try{
b = Grayscale.CommonAlgorithms.Y.Apply(b);
}finally{
if (old != s.sourceBitmap) old.Dispose();
}
new SobelEdgeDetector().ApplyInPlace(b);
str = s.settings["a.threshold"]; //radius
if (!string.IsNullOrEmpty(str) && int.TryParse(str, NumberStyles.Integer, NumberFormatInfo.InvariantInfo, out i) && i > 0)
new Threshold(i).ApplyInPlace(b);
}
//Canny Edge Detector only supports 8bpp grayscale images.
//true/false
if ("true".Equals(s.settings["a.canny"], StringComparison.OrdinalIgnoreCase)) {
Bitmap old = b;
try {
b = Grayscale.CommonAlgorithms.Y.Apply(b);
} finally {
if (old != s.sourceBitmap) old.Dispose();
}
new CannyEdgeDetector().ApplyInPlace(b);
}
//true/false - duplicate with SimpleFilters?
if ("true".Equals(s.settings["a.sepia"], StringComparison.OrdinalIgnoreCase))
new Sepia().ApplyInPlace(b);
//true/false
if ("true".Equals(s.settings["a.equalize"], StringComparison.OrdinalIgnoreCase))
new HistogramEqualization().ApplyInPlace(b);
///White balance adjustment
var whiteAlg = s.settings.Get<HistogramThresholdAlgorithm>("a.balancewhite");
var whiteVal = s.settings.Get<double>("a.balancethreshold");
if (whiteAlg != null || whiteVal != null) {
var bal = new AutoWhiteBalance(whiteAlg ?? HistogramThresholdAlgorithm.Area);
if (whiteVal != null) bal.LowThreshold = bal.HighThreshold = whiteVal.Value / 100;
bal.ApplyInPlace(b);
}
str = s.settings["a.posterize"]; //number of colors to merge
if (!string.IsNullOrEmpty(str) && int.TryParse(str, NumberStyles.Integer, NumberFormatInfo.InvariantInfo, out i) && i > 0) {
SimplePosterization sp = new SimplePosterization();
if (i < 1) i = 1;
if (i > 255) i = 255;
sp.PosterizationInterval =(byte)i;
sp.ApplyInPlace(b);
}
//Pixellate doesn't support 32-bit images, only 24-bit
//str = s.settings["a.pixelate"]; //number of colors to merge
//if (!string.IsNullOrEmpty(str) && int.TryParse(str, out i)){
// if (i < 2) i = 2;
// if (i > 32) i = 32;
// new Pixellate(i).ApplyInPlace(s.destBitmap);
//}
float contrast = s.settings.Get<float>("a.contrast", 0);
float brightness = s.settings.Get<float>("a.brightness", 0);
float saturation = s.settings.Get<float>("a.saturation", 0);
if (contrast != 0 || brightness != 0 || saturation != 0){
HSLLinear adjust = new HSLLinear();
AdjustContrastBrightnessSaturation(adjust, contrast, brightness, saturation, "true".Equals(s.settings["a.truncate"]));
adjust.ApplyInPlace(b);
}
//TODO - add grayscale?
//For adding fax-like thresholding, use BradleyLocalThresholding
//For trimming solid-color whitespace, use Shrink
}
/// <summary>
/// Returns true if the average energy of the image is below the given threshold
/// </summary>
/// <param name="image"></param>
/// <param name="threshold"></param>
/// <returns></returns>
private bool IsBlank(byte[] image, byte threshold)
{
var ms = new MemoryStream(image);
using (var b = new Bitmap(ms))
{
using (var gray = Grayscale.CommonAlgorithms.BT709.Apply(b))
{
new SobelEdgeDetector().ApplyInPlace(gray);
var p = new SimplePosterization(SimplePosterization.PosterizationFillingType.Average);
p.PosterizationInterval = 128;
p.ApplyInPlace(gray);
return gray.GetPixel(0, 0).R < threshold;
}
}
}
public ImagePreprocessor()
{
gScale = new Grayscale(0.2125, 0.7154, 0.0721);
sobelDetector = new SobelEdgeDetector();
posterization = new SimplePosterization();
}
