CODEWITHSUNDEEP
javaimage-processing
Abhinav Rastogi
Abhinav Rastogi

Reputation: 35

what is the significance of (k<<24)>>>24 in remote sensing image reading?

In general, why do we first left-shifted it only to be right-shifted again? Is it related to something like ensuring that pixel value is positive? code Snipped->

for(k=0; k<Width; k++)
{
    if(shiftFlag != 8)
    {
        p1 = pix_rgb[i][2*k] << 24;
        p2 = (pix_rgb[i][2*k+1] <<24 ) >>> 8;
        tempCount = p1 | p2;
        tempCount = tempCount >>> 16;
    }
    else
        tempCount = (pix_rgb[i][k] << 24) >>> 24;

    if(tempCount>maxBand[i])
        maxBand[i]=tempCount;

    if(tempCount<minBand[i])
       minBand[i]=tempCount;
}

Upvotes: 2

Views: 65

Answers (1)

Pshemo
Pshemo

Reputation: 124275

Based on name of pix_rgb I am assuming that pix_rgb[i][k] holds an int represesnting color which usually on 32 bits (which is size of int) is written in form 

AAAAAAAARRRRRRRRGGGGGGGGBBBBBBBB
|       |       |       |
|       |       |       blue
|       |       green
|       red
alpha/transparency

By pix_rgb[i][k] << 24 you are shifting all bits to left and set most right 24 bits to 0.

So AAAAAAAARRRRRRRRGGGGGGGGBBBBBBBB will become

BBBBBBBB000000000000000000000000
        ^^^^^^^^^^^^^^^^^^^^^^^^ <<24

Now with (pix_rgb[i][k] << 24) >>> 24 you can think of it as BBBBBBBB000000000000000000000000 >>> 24 where you are shifting bits to right but at the same time you are guaranteed that most left bits will be filled with 0 (if we would use >> 24 we could fill it with 1 if first B would also be 1).

So BBBBBBBB000000000000000000000000 will be changed into 

000000000000000000000000BBBBBBBB
^^^^^^^^^^^^^^^^^^^^^^^^ >>>24

In other words we got int which holds value which represents only blue color.

In short

  • pix_rgb[i][k] << 24 was used to remove all bits except BBBBBBBB
  • >>>24 was used to set BBBBBBBB back at lower indexes of int so we could treat it as value from range 0-255.

Upvotes: 2

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