On the Rigaku website http://www.rigaku.com/downloads/software/ present some utilities for converting. For example, "dtrek2jpeg" may be useful. Documentation placed into zip-file. Obtained JPG file easily convert to TIFF by means of free software, for example, IrFanViewer : http://www.irfanview.com/ .

Thank you Alexey. I tried "dterk2jpeg" .

Unfortunately, I found that the software is not suitable for my purpose. In JPEG format, each pixel is 8 bit. Therefore, the information in the original file is lost. Because I want to convert the image for analytical purpose, loss of the information in 16 bit format should be avoided.

Thank you all, I could solve the problem by myself.

ImageJ can be used for the conversion. We have to know the image size (pixel * pixel)  in advance. Then we can import the img file by "File -> Import -> Raw". The image type is 16 bit Unsigned. Skip byte is the size of one line, i.e., 2 (byte) * pixels of width.

The following text is saved as a macro file in advance.

---------

// Correct a Rigaku IMG file to handle in ImageJ.

// IMG file must be read as 16bit Unsigned.

// Skip byte is the size of one line, i.e., 2 (byte) * pixels of width.

w = getWidth();

h = getHeight();

mask = 32767;

for (y=0; y

Thank you Nita,

One of my problem was to handle the Rigaku IMG file by FIT2D. The software can read  IMG files by Fuji and Hamamatsu but Rigaku IMG file is not supported.

Now, I found that the format of Rigaku IMG file changes according to the type of instruments. The above method is valid for R-AXIS.