5 Tips for PHP Image Effect, Watermark, Resize

Estimated reading time: 7 minutes

 

 

 

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Copy and Re-Sample

Suppose the original file is of JPEG format, and its size is 600×400. We want to resize it to be 300×200. First, a GD function imagecreatefromjpeg() reads the image file to produce an image resource $img.

Next, the other GD function imagecreatetruecolor() create a template of new size. it is referred as a destination image file.

Finally, copying and re-sampling are done. The PHP GD library function imagecopyresampled() copies the source area of { xpos:0, ypos:0, width:600, height:600 } to the destination area of { xpos:0, ypos:0, width:300, height:200 }. That obviously resize the image.

// Image Resize
function image_resize($src, $w, $h) {
    $img = imagecreatefromjpeg($src);
    $oldw = imagesx($img);
    $oldh = imagesy($img);
    $template = imagecreatetruecolor($w, $h);
    imagecopyresampled($template, $img, 0, 0, 0, 0, $w, $h, $oldw, $oldh);
    return $template;
}
imagejpeg(image_resize("$path/pic1.jpg", 300, 200), "$path/pic1-resize.jpg");

The function image_resize() return an image resource. Therefore, you can display it on screen layout, or just save the image resource as a resized JPEG file as the above does.

 

 

Re-Sample with The Same Size

Let’s consider the requirement of cutting part of an image. We generate image resources of source and destination at first. Next, the GD function imagecopyresampled() copies the source area of { xpos:80, ypos:110, width:250, height:210 } to the destination area of { xpos:0, ypos:0, width:250, height:210 }. That indeed cuts part of an image to create another image.

// Image Crop
function image_crop($src, $x, $y, $w, $h) {
    $img = imagecreatefromjpeg($src);
    $template = imagecreatetruecolor($w, $h);
    imagecopyresampled($template, $img, 0, 0, $x, $y, $w, $h, $w, $h);
    return $template;
}
imagejpeg(image_crop("$path/pic1.jpg", 80, 110, 250, 210), "$path/pic1-crop.jpg");

The function image_crop() return an image resource. Therefore, you can display it on screen layout, or just save the image resource as a cut JPEG file.

 

 

Change JPEG to PNG

Suppose that we convert JPEG format to PNG format for image files. Other combinations of conversion are left as your exercises.

The PHP function file_get_contents() gets binary data from a JPEG image file. And then the GD function imagecreatefromstring() generates an image resource from an image file. Supported source image types are JPEG, PNG, GIF, BMP, WBMP, GD2, and WEBP.

Finally, the GD function imagepng() save the image resource into a destination PNG image file.

// Image Convert
function image_conv_png($src, $dst, $quality) {
    $data = file_get_contents($src);
    $img = imagecreatefromstring($data);
    imagepng($img, $dst);
}
image_conv_png("$path/pic1.jpg", "$path/pic1-png.png", 50);

The conversion involves a quality factor. It ranges from 0 to 99, so the quality of 50 indicates normal or middle level.

 

 

Mathematical Filters

A PHP Image filter is the algorithm used to add a specific effect on images. They consist of brightness, contrast, and so on. To implement it on an image, you can use PHP function imagefilter() with different effect parameters.

• IMG_FILTER_BRIGHTNESS: Changes the brightness of the image.
• IMG_FILTER_CONTRAST: Changes the contrast of the image.
• IMG_FILTER_GRAYSCALE: Converts the image into grayscale.
• IMG_FILTER_EDGEDETECT: Uses edge detection to highlight the edges in the image.
• IMG_FILTER_EMBOSS: Embosses the image.
• IMG_FILTER_GAUSSIAN_BLUR: Blurs the image using the Gaussian method.
• IMG_FILTER_MEAN_REMOVAL: Uses mean removal to achieve a “sketchy” effect.
• IMG_FILTER_SMOOTH: Makes the image smoother.

In this example, we choose only the embossed feature to let you know how it works. Compared with the original photo, sculpted scenes are raised above the background plane.

The PHP function imagecreatefromjpeg() generate an image resource from an image file. Then another PHP function imagefilter() modifies the image resource with specified effect.

// Image Filter
function image_filter($src, $effect) {
    $img = imagecreatefromjpeg($src);
    imagefilter($img, $effect);
    return $img;
}
imagejpeg(image_filter("$path/pic1.jpg", IMG_FILTER_EMBOSS), "$path/pic1-filter.jpg");

The function image_filter() return an image resource. Therefore, you can display it on screen layout, or just save the image resource as a filtered JPEG file.

 

 

Create a Text Stamp

Usually, the purpose of putting watermarks on images is to prevent pictures from stealth or misappropriation. To do it, we want to create am text-based image resource as a stamp.

First, a file of truetype font is necessary. The GD function imagecreatetruecolor() create a stamp template of 300×60 as an image resource.

The GD function imagecolorallocate() create colors for the image resource. And then the function imagefilledrectangle() draws a rectangle with white background. Finally, put the text shadow and text string subsequently. Both of them are of a font size and an adjusted angle.

// Image Water Mark
function image_watermark($src, $dst, $stamp_x, $stamp_y){
    $fontfile = dirname(__FILE__) . "/arial.ttf";
    $text = "Easy Code Share";
    $stamp_w = 300;
    $stamp_h = 60;
    $stamp = imagecreatetruecolor($stamp_w, $stamp_h);
    $white = imagecolorallocate($stamp, 255, 255, 255);
    $grey = imagecolorallocate($stamp, 128, 128, 128);
    imagefilledrectangle($stamp, 0, 0, 300, $stamp_h, $white); // create rectangle
    $angle = -4;
    $fsize = 26; // font size
    $font_x = 10;
    $font_y = 30;
    // add shadow
    imagettftext($stamp, $fsize, $angle, $font_x+1, $font_y+1, $grey, $fontfile, $text);
    // add text
    imagettftext($stamp, $fsize, $angle, $font_x, $font_y, $white, $fontfile, $text);
    // merge image and stamp
    $img = imagecreatefromjpeg($src);
    $pct = 50;
    imagecopymerge($img, $stamp, $stamp_x, $stamp_y, 0, 0, $stamp_w, $stamp_h, $pct);
    imagejpeg($img, $dst);
}
image_watermark("$path/pic1.jpg", "$path/pic1-watermark.jpg", 150, 100);

 

Merge Stamp and Image

Along with the prepared stamp image resource, we can merge it and an image resource $img form the original image by GD function imagecopymerge(). Moreover, the parameter $pct a is transparency factor. If pct = 0, no action is taken, when 100 there is no transparency. We choose a middle level of 50.

 

 

Suggested Reading

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