read and save img file

when I use the command fopen and fread to input the image with img format,the mat file shows the streched values (from 0-255)rather than pixel values. How can I open an img file and have the pixel values. and How can I save my output as img format?

[Jan]

What exactly is the "img" format? Do you mean the Apple disk image files? Which MAT-files shows what and what are "streched" values? What does "pixel values" mean?

Please edit the question and add more details.

[Hana]

I have a satellite image with .img format. streched values are on the scale of 0-255 .if you click to identify any pixel values in arcgis then you have two set of values,one is streched and one is the value of the pixel. I read my image as follow,but the mat file in matlab shows the streched values and not the pixel values of the image. fid2=fopen('tb420_4.img'); tb = fread(fid2,[6100 2505]);