HistogramCommand Class

Summary

Creates an array that charts how many times each intensity level occurs in an image. This class can chart red, green, and blue separately or together. It is used for all resolutions, including 12 and 16-bit grayscale.

Syntax

Objective-C

C++/CLI

Java

Python

public class HistogramCommand : RasterCommand

@interface LTHistogramCommand : LTRasterCommand

public class HistogramCommand 
    extends RasterCommand

public ref class HistogramCommand : public RasterCommand

class HistogramCommand(RasterCommand):

Remarks

For 1, 2, 3, 4, 5, 6, 7, 8, 16, 24, and 32 bit color images, intensity levels range from 0 to 255. Therefore, the resulting array has 256 items, indexed by intensity value. The value of each item is the number of occurrences of the intensity level.
For 48 and 64-bit images, the intensity levels range from 0 to 65535. Therefore, the resulting array has 65536 items, indexed by intensity value. The value of each item is the number of occurrences of the intensity level.
This class also works on 12 and 16-bit grayscale images. Intensity values in these images can range from 0 to (2^16 - 1) for 16-bit grayscale or from 0 to (2^12 - 1) for 12-bit grayscale. The LowBit and HighBit of this image identify which bits in a 12-bit or 16-bit entry are used. The LowBit and HighBit can be obtained by using the MinMaxCommand or by looking at the corresponding properties in the RasterImage class itself.
Specifically, the table must hold at least 2^(HighBit - LowBit + 1) entries if HistogramCommandFlags.LowHighBits is set in the Channel Property. If HistogramCommandFlags.AllBits is set in the Channel Property, the table must hold at least 4096 for 12-bit images and 65536 for 16-bit images.

For example, suppose HistogramCommandFlags.LowHighBits is set in the Channel property and you have a 16-bit grayscale image with LowBit = 2 and HighBit = 7. There are 2^(7-2+1) = 64 possible grayscale intensities. The table must therefore hold at least 64 entries. The number of grayscale values with bits 2 - 7 set to 0 can be found in Histogram [0]. The number of grayscale values with bit 2 set to 1 and bits 3 - 7 set to 0 can be found in Histogram [1], and so on up to Histogram [63]. Since the low bit is 2 and the high bit is 7, bits 0, 1, and bits 8 - 15 must all be 0. Therefore the values set in bits 2 - 7 determine the intensities present in the image. In the table below, the gray columns represent those bits that are always 0 for the image. The columns bit 7 through bit 2 represent possible settings for those bits. The last column gives the location within the Histogram array of the number of grayscale values having the corresponding settings. For example, Histogram [0] contains the number of grayscale values of intensity 0 (all bits set to 0). Histogram [1] contains all the grayscale values with intensity 4 (the 2 bit position set to 1). Histogram [2] contains all the grayscale values with intensity 8 (the 3 bit set to 1 and the remaining bits set to 0) and so on.

bits 8 - 15	bit 7	bit 6	bit 5	bit 4	bit 3	bit 2	bit 1	bit 0	count location in Histogram
all 0s	0	0	0	0	0	0	0	0	Histogram [0]
all 0s	0	0	0	0	0	1	0	0	Histogram [1]
all 0s	0	0	0	0	1	0	0	0	Histogram [2]
all 0s	0	0	0	0	1	1	0	0	Histogram [3]
all 0s	0	0	0	1	0	0	0	0	Histogram [4]
_	0	0	0	0	0	0	_	_	and so on
all 0s	1	1	1	1	1	1	0	0	Histogram [63]

As another example, suppose you have a 16-bit grayscale image with LowBit = 0 and HighBit = 15. The table must hold 2^16 = 65,536 integer values.
This class supports 12 and 16-bit grayscale and 48 and 64-bit color images. Support for 12 and 16-bit grayscale and 48 and 64-bit color images is available only in the Document/Medical toolkits.
This command does not support 32-bit grayscale images.

For more information, refer to Changing Brightness and Contrast. For more information, refer to Grayscale Images.

Example

Run the HistogramCommand on an image to get the red-channel histogram.

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing.Color; 
 
 
public void HistogramCommandExample() 
{ 
   // Load an image 
   RasterCodecs codecs = new RasterCodecs(); 
   codecs.ThrowExceptionsOnInvalidImages = true; 
 
   RasterImage image = codecs.Load(Path.Combine(LEAD_VARS.ImagesDir, "Master.jpg")); 
 
   // Prepare the command 
   HistogramCommand command = new HistogramCommand(); 
   long[] histogramValues; 
   //Create the red-channel histogram. 
   command.Channel = HistogramCommandFlags.Red | HistogramCommandFlags.AllBits; 
   command.Run(image); 
   codecs.Save(image, Path.Combine(LEAD_VARS.ImagesDir, "Result.jpg"), RasterImageFormat.Jpeg, 24); 
   histogramValues = command.Histogram; 
 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS22\Resources\Images"; 
}