Histogram is used to show the proportion of pixels in image for all gray levels, it describes the distribution of gray levels of all image pixels. The details of dark tone images concentrate in the low gray area, while the details of light tone images concentrate in the high gray area. It will help the users to make tone adjustment with the distribution of the gray level of image.
Histogram editing will transform the original image into another image based on the given histogram distribution form. This method is mainly used to adjust the image with dark tone or light tone. For example, the gray value of a dark tone image concentrate in the range of 30~160, if the gray level of output image is evenly distributed at the range of 10~240, it will get an image with high contrast and tone smooth transition, which is helpful for extracting the details.
The system provides the function of histogram editing, which can transform the gray range of the input image (including non byte image type) into other range (commonly in the range of 0~255).
The operation is explained as follows:
Enter the system main interface, import an image to be processed.
Click the channel in the Layer panel.
Click on the Histogram property page in the Property panel, the corresponding image histogram will be displayed at the black rectangle box, as shown in figure.
The yellow curve in the histogram represents the transformation curve, the light blue color represents the original histogram, and the green color represents the transformed histogram.
Trim
It is used to eliminate the proportion of the noise. By default, the value is 0.02, which represents about 2% pixels distributed at both sides will be eliminated as noise, the corresponding gray value will be replaced by the adjacent gray values.
Input Min
By default, the system will regard the minimum gray value of the input image as the input minimum. Users can set the input minimum based on the requirement; at this time, the system will eliminate those pixels to which their gray values are less than the inputted minimum value as noise. So the input minimum already set should not be less than the minimum gray value of the input image, and also not large than the maximum gray value of the input image.
Input Max
By default, the system will regard the maximum gray value of the input image as input maximum. Users can set the input maximum based on the requirement, in this case, the system will eliminate those pixels to which their gray values are larger than inputted maximum value as noise. So the input maximum already set should not be larger than the maximum gray value of the input image, and also not less than minimum gray value of the input image.
Output Min
The minimum gray value of output image. The value is an integer in the range of 0~255. Users can set output minimum based on the requirement, the system will set all gray values which are less than the output minimum as output minimum.
Output Max
The maximum gray value of the output image. The value is an integer in the range of 0~255. Users can set output maximum based on the requirement, the system will set all the gray values which are larger than the output maximum as output maximum.
ROI
Select a certain regions of the interest (ROI) in image, and then match its histogram to the entire image. By default, it is None.
Users can set the histogram input and output range with the editing frame. Based on the setup, the system will adjust the output histogram, and display the result in image display window in real time (Input a value in the editing box and press “Enter” button, you can view the result in image display window).
Edit the transformation curve manually. Just press the left mouse key and drag the small rectangle box of the yellow curve to edit the gray value, the system will process the image based on the adjusted curve and display the result in image display window, as shown in figure.
Manual
editing LUT (Look-up-Tables) directly. If it is not convenient to edit
the curve in the histogram or the result does not satisfy the expectation,
users can click the button 
to open the LUT (Look-up
Tables, shortened form is LUT) for exact edit of the gray value.
If the image to be processed is in the color layer or gray layer, the system will pop up the LUT dialog box, as shown in figure.
The Break Points table lists all the coordinates (X, Y) of the break points on the curve.
In the LUT table, it lists both the input value and the output value to indicate the gray value change. Input represents the original gray values; Output represents the changed gray values. Users can modify the output gray value based on the requirement.
After editing, click Ok button, the system will close the dialog box and display the result in image display window.
If users want to save the
current change, click 
button, then assign a
directory and filename in the pop up Save As dialog box, the system
will save the current LUT for later use. When users open the image next
time, click 
button, load the saved LUT and apply
that to the current displayed image file to show the result after edit.
Certainly, it also can be used to other images (Please refer to Image Enhancement for details).
Click Cancel button to exit the dialog box directly without saving the edit result.
If the image is a pseudo color image, the system will pop up the Pseudocolor Table, as shown in figure.
In this table, it lists all the gray values for different color layers represented by each index value in the peseudo image, i.e. Blue, Green, and Red channel. Users can modify the gray value in the table, when the cursor leaves the editing cell box or click “Enter” button, it will display the modified result in the image display window.