The system provides the function of histogram matching, that means it can apply the histogram of an image or an area to another image. It will make the tone of two images consistent. This method can be applied to the histogram matching of single band image as well as the images with multi-bands. The detailed operation procedure is explained as follows:
Select the target histogram.
Matching in a single band. Click the channel to be matched in the Layer panel, then click Linear button in the Histogram page of the Layer panel, then click Histogram Matching menu option in the pop up menu, the system will pop up the Histogram Matching dialog box, as shown in figure.
The file name and its layer and channel of the required image will be displayed in the To Histogram edit box (if matching the whole layer, no channel will be contained).
Histogram matching with all layers. Click the layer to be matched in the Layer panel, click the right mouse button, and then click the Enhance > Histogram Matching menu option in the pop up menu, the system will open the Histogram Matching dialog box. At this time, the To Histogram bar dialog box will display the required matching image’s filename and the corresponding layer.
Select the original histogram.
Select an image for histogram matching in the Layer or File panel (either file or a band), the path (or band name) of the selected image file will be displayed in the histogram bar.
If it has defined the regions of interest (ROI) in the image of the selected original histogram, the ROI pull down box will be activated then, users can select the histogram of the ROI as the original histogram (By default, it is None, which means the entire image histogram is taken as original histogram).
After selecting the original histogram, the dialog box will look like figure.
Histogram matching.
After selecting the corresponding image data at the target histogram (To Histogram) and the original histogram (From Histogram), click Apply button, the system will process histogram matching automatically and display the result in image display window in real time.
If the result is not satisfied, you can reset the original histogram image in Layer or File panel to rematch the image until it reaches the expectation.
After matching the histogram, you can exit from the module with Close button.
NOTE
If the original histogram has only one band, while the target histogram has many bands; the system will match the original histogram to all bands of the target histogram.
If the target histogram and the original histogram both have many bands, then the system will use the bands of original histogram to matching the target histogram one by one, i.e. the first band will match the first band of the target histogram (the band of first channel), the second band will match the second band of the target histogram (the band of second channel). If the number of bands in the original histogram is less than the target histogram, then it will use the last band histogram to match the rest bands of the target histogram.