Two choices and differences for generating thumbnails with GD under PHP _php tutorial

The GD extension of PHP provides two functions to scale an image:

Imagecopyresized (destsrcdxdysxsyDWDH  SWsh);
Imagecopyresampled (destsrcdxdysxsyDW  dhSWsh);

The imagecopyresized () function works in all GD versions, but its scaled image algorithm is coarser and may cause jagged edges of the image. GD 2.x has a new imagecopyresampled () function, and its pixel interpolation algorithm gets a smoother image edge (but the function is slower than imagecopyresized () .

To take a look at an example, we'll reduce this figure by four times times:

$SRC= Imagecreatefromjpeg(' php.jpg ');

$width= Imagesx($src);
$height= Imagesy($src);
$x= $width/2; $y= $height/2;
$DST= Imagecreatetruecolor($x,$y);
imagecopyresized($DST,$src,0,0,0,0,$x,$y,$width,$height);
//imagecopyresampled ($DST, $SRC, 0,0,0,0, $x, $y, $width, $height);

Header(' Content-type:image/jpeg ');
imagejpeg($DST,'', -);
?>

Original:


Use ImageCopyResized()函数生成的结果：



使用 ImageCopyResampled()函数生成的结果：




It's obvious that two functions produce a different image than the one you see. ImageCopyResampled()函数生成的结果比较平滑，效果较好。



By the way, an effect is represented by an ASCII representation of the image. Imagecolorat () has a very interesting use, it can cycle check
The color of each pixel in the image, and then manipulate the color data.

Source:

  
            $im
 = Imagecreatefromjpeg(' test1.jpg ');
$DX= Imagesx($im);
$dy= Imagesy($im);
for ($y= 0; $y<$dy; $y++) {
for ($x=0; $x<$DX; $x++) {
         $col= Imagecolorat($im, $x, $y);
         $rgb= Imagecolorsforindex($im,$col);
         printf('*',
                 $rgb[' Red '],$rgb[' Green '],$rgb[' Blue ']);
}
Echo"
\ n ";
}
Imagedestroy($im);
?>
 

Very interesting, hehe.

http://www.bkjia.com/PHPjc/318380.html www.bkjia.com true http://www.bkjia.com/PHPjc/318380.html techarticle the GD extension of PHP provides two functions to scale the image: Imagecopyresized (dest, src, dx, dy, sx, SY, DW, DH, SW, SH); imagecopyresampled (dest, src, dx, dy, sx, SY, DW ...)

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