I have a large set (>10000) of uncompressed 8 bit images. Their size is 1600*1200 pixels.

The first 24 pixels in the upper most line starting from left contain some important information (time stamp etc.) about the image.

I want to read out all byte values of these 24 pixels.

Finally I want to save all byte data as right aligned numbers into a text file, a single line with 24 numbers for each image.

I CANNOT READ IN ALL IMAGES INTO THE MEMORY AT ONCE BECAUSE OF MEMORY PROBLEMS.

For testing I have uploaded a set of 1000 cropped images, each having a dimension of 50*50 pixels. They can be downloaded from here: https://drive.google.com/open?id=0B9wKP6yNcpyfUUlsQU1iVWJ0b2M

I have two questions:

**- how can I improve (speed up) my code?**

**- what is the most straightforward solution to save the byte values right aligned into a text file?**

My code is: 

    ChoiceDialog[{FileNameSetter[Dynamic[imageDir], "Directory"], Dynamic[imageDir]}];
    SetDirectory[imageDir];
    
    fNames = FileNames["*.png"];
    n = Length[fNames];

    timeStampValues = Array[0 &, {n, 24}];
    SetSharedVariable[timeStampValues];
    
    ParallelDo[
       
       byteValues = Import[fNames[[i]], "Data"];
       timeStampValues[[i, All]] = Flatten@byteValues[[1, 1 ;; 24]];
       
       , {i, 1, n}
    ]; // AbsoluteTiming
    
    {17.7253, Null}

    (* Saving byte values into text file - can that be done easier?*)
    
    formatted = Map[NumberForm[#, {3, 0}, NumberPadding -> {" ", "0"}, 
       NumberPoint -> ""] &, timeStampValues, {2}]
    
    Export[StringJoin[imageDir, "\\timeStampBytes.txt"], formatted, "Table"];