how can I modify the brightness&contrast automatically on my images with fiji macro?

I try to write a very simple macro with Fiji in order to merge channels and enhance contrast automatically.

dir  = getDirectory("Select input directory"); out  = getDirectory("Select destination directory");
files  = getFileList(dir);
//foreach tiff couple files
for (j=0; j<lengthOf(dir);j+2) {
    channel1 = dir+files[j];
    channel2 = dir+files[j+1];
    open(channel1); 
    open(channel2);
    run("Enhance Contrast", "saturated=0.35"); // the same for the channel1
    run("Apply LUT", "stack"); // the same for the channel1
    run("Merge Channels...", "c1="+channel1+" c2="+channel2);
    run("Z Project...", "projection=[Sum Slices]");
    saveAs("Tiff", out+"merge"+files[j]);
    run("Close");
}

With "enhance contrast", I don't know how I can use the button "auto" of the brightness&contrast window in the macro. The channel 2 is stronger than the first.

And with "apply LUT", an error occur when I have this line : "The display range must first be updated using Image>Adjust>Brightness/Contrast or threshold levels defined using Image>Adjust>Threshold." I changed the threshold level and it still doesn't work...

What could you suggest to me ?

The Apply Lut command (source) gives this error if the display min and max are 0 and 255. This could occur if your image already has high contrast. Below I added a condition using getMinAndMax where it skips the Apply step if the display range is unchanged (i.e. 0-255).

With "enhance contrast", I don't know how I can use the button "auto" of the brightness&contrast window in the macro.

According to the documentation, run("Enhance Contrast", "saturated=0.35") is the same as clicking Auto on the B&C window.

I'm not clear if you want to repeat this process on all the images or just the 2nd channel. Below is a macro that enhances contrast on each channel individually, and fixes some issues with the loops.

dir  = getDirectory("Select input directory"); out  = getDirectory("Select destination directory");
files  = getFileList(dir);
//foreach tiff couple files
    for (j=0; j<lengthOf(files);j+=2) { //fixed loop length and incrementor
    channel1 = dir+files[j];
    channel2 = dir+files[j+1];
    open(channel1); 
    image1 = getTitle(); // get the window name
    open(channel2);
    image2 = getTitle(); // get the window name

    selectWindow(image1); // focus on the first channel
    run("Enhance Contrast", "saturated=0.35 process_all"); // process all slices
    getMinAndMax(min,max);  // get display range
    if (min != 0 && max != 255) {  // check if the display has been changed
        run("Apply LUT", "stack"); 
        }

    selectWindow(image2); // repeating for the 2nd channel
    run("Enhance Contrast", "saturated=0.35 process_all"); // process all slices
    getMinAndMax(min,max); // get display range
    if (min != 0 && max != 255) {  // check if the display has been changed
        run("Apply LUT", "stack"); 
        }

    run("Merge Channels...", "c1="+image1+" c2="+image2); // use window names rather than full paths
    run("Z Project...", "projection=[Sum Slices]");
    saveAs("Tiff", out+"merge"+files[j]);
    run("Close All"); // make sure everything is closed
}