Loop through specified area of pixels - php

Question

I've made a search by color feature on my photo website. To do this, I looped through all the pixels in one image and recorded the top 10 in my database. The problem I have is that because my photos have people subjects, my searchers are really searching for colors of the subject, rather than the background (sky, paving, grass etc). I know this will be very hard to eliminate completely but I'm thinking I need to change the color slightly to give better results.
Please see this example of one photo:
The example on the left is what I was doing, collecting ALL pixels. Black and grays took up the top 3 colors in that selection, a shade of pink was 4th and navy blue from the background girl's dress was 5th - I only collect the top 5 colors and my main color wasn't really ranked that good. If I could change the way I loop through the pixels, to select only the colors in the green box (right), I think it would make a slight bit of difference in my collection. This is where I'm struggling to see the math.
I was doing this, to loop through all pixels:
$size = #getimagesize($imageFile);
for ($x = 0; $x < $size[0]; $x += $granularity) {
for($y = 0; $y < $size[1]; $y += $granularity) {
// do stuff here
}
But I need to change this to take roughly 5% off the top and bottom and roughly 8-10% of the sides and then loop through the new selection.
I did start this but then stopped because I wasn't sure about my calculations returning odd numbers or number likes 1.030044858.
This is how far I got and hoped somebody can help clean it up and get me over the line:
$granularity = 4;
$granularity = max(1, abs((int)$granularity));
$size = #getimagesize($imageFile);
$sizeX = $size[0];
$sizeY = $size[1];
$xPerCent = 8; // for me to set & adjust
$yPerCent = 5; // for me to set & adjust
$xSelectionWidth = ($sizeX/100) * $xPerCent;
$xSelectionWidth = $sizeX - ($xSelectionWidth * 2);
$xSelectionHeight = ($sizeY/100) * $yPerCent;
$xSelectionHeight = $sizeY - ($ySelectionHeight * 2);
$xSelectionStart = 0;
$xSelectionEnd = 0;
$ySelectionStart = 0;
$ySelectionEnd = 0;
for($x = 0; $x < $size[0]; $x += $granularity) {
for($y = 0; $y < $size[1]; $y += $granularity) {
// do stuff here
}
}

Answer 1

If you want to ignore something in a picture, I suggest you to convert it to B&W and take the biggest white area (you will need to set details of the convertion to be sure you do not get all non already white color as black).
I mean red, and skin color should be set as white and violet as black. In this case, the background and any dark surface would be black. Read http://www.switchonthecode.com/tutorials/csharp-tutorial-convert-a-color-image-to-grayscale its a great introduction but, I am talking about real Black and white so, you may adjust/adapt this one.
This will greatly help you to get focus on the right part of the image.
The more accurate the B&W form recognition, the better you can identify the subject you wat color from. Please read http://en.wikipedia.org/wiki/Pattern_recognition for detailed infos on pattern recognition.
Get the set of coordinates you want to look at in the original image.
Sory I am not a PHP person, I can not be more specific in this way but, I hope this will help you...