Урок - Image Manipulation Class

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CodeIgniter's Image Manipulation class lets you perform the following actions:

  • Image Resizing
  • Thumbnail Creation
  • Image Cropping
  • Image Rotating
  • Image Watermarking

All three major image libraries are supported: GD/GD2, NetPBM, and ImageMagick

Note: Watermarking is only available using the GD/GD2 library. In addition, even though other libraries are supported, GD is required in order for the script to calculate the image properties. The image processing, however, will be performed with the library you specify.

Initializing the Class

Like most other classes in CodeIgniter, the image class is initialized in your controller using the $this->load->library function:

$this->load->library('image_lib');

Once the library is loaded it will be ready for use. The image library object you will use to call all functions is: $this->image_lib

Processing an Image

Regardless of the type of processing you would like to perform (resizing, cropping, rotation, or watermarking), the general process is identical. You will set some preferences corresponding to the action you intend to perform, then call one of four available processing functions. For example, to create an image thumbnail you'll do this:

$config['image_library'] = 'gd2';
$config['source_image'] = '/path/to/image/mypic.jpg';
$config['create_thumb'] = TRUE;
$config['maintain_ratio'] = TRUE;
$config['width'] = 75;
$config['height'] = 50;

$this->load->library('image_lib', $config);

$this->image_lib->resize();

The above code tells the image_resize function to look for an image called mypic.jpg located in the source_image folder, then create a thumbnail that is 75 X 50 pixels using the GD2 image_library. Since the maintain_ratio option is enabled, the thumb will be as close to the target width and height as possible while preserving the original aspect ratio. The thumbnail will be called mypic_thumb.jpg

Note: In order for the image class to be allowed to do any processing, the folder containing the image files must have write permissions.

Note: Image processing can require a considerable amount of server memory for some operations. If you are experiencing out of memory errors while processing images you may need to limit their maximum size, and/or adjust PHP memory limits.

Processing Functions

There are four available processing functions:

  • $this->image_lib->resize()
  • $this->image_lib->crop()
  • $this->image_lib->rotate()
  • $this->image_lib->watermark()
  • $this->image_lib->clear()

These functions return boolean TRUE upon success and FALSE for failure. If they fail you can retrieve the error message using this function:

echo $this->image_lib->display_errors();

A good practice is use the processing function conditionally, showing an error upon failure, like this:

if ( ! $this->image_lib->resize())
{
    echo $this->image_lib->display_errors();
}

Note: You can optionally specify the HTML formatting to be applied to the errors, by submitting the opening/closing tags in the function, like this:

$this->image_lib->display_errors('<p>', '</p>');

Preferences

The preferences described below allow you to tailor the image processing to suit your needs.

Note that not all preferences are available for every function. For example, the x/y axis preferences are only available for image cropping. Likewise, the width and height preferences have no effect on cropping. The "availability" column indicates which functions support a given preference.

Availability Legend:

  • R - Image Resizing
  • C - Image Cropping
  • X - Image Rotation
  • W - Image Watermarking
PreferenceDefault ValueOptionsDescriptionAvailability
image_library GD2 GD, GD2, ImageMagick, NetPBM Sets the image library to be used. R, C, X, W
library_path None None Sets the server path to your ImageMagick or NetPBM library. If you use either of those libraries you must supply the path. R, C, X
source_image None None Sets the source image name/path. The path must be a relative or absolute server path, not a URL. R, C, S, W
dynamic_output FALSE TRUE/FALSE (boolean) Determines whether the new image file should be written to disk or generated dynamically. Note: If you choose the dynamic setting, only one image can be shown at a time, and it can't be positioned on the page. It simply outputs the raw image dynamically to your browser, along with image headers. R, C, X, W
quality 90% 1 - 100% Sets the quality of the image. The higher the quality the larger the file size. R, C, X, W
new_image None None Sets the destination image name/path. You'll use this preference when creating an image copy. The path must be a relative or absolute server path, not a URL. R, C, X, W
width None None Sets the width you would like the image set to. R, C
height None None Sets the height you would like the image set to. R, C
create_thumb FALSE TRUE/FALSE (boolean) Tells the image processing function to create a thumb. R
thumb_marker _thumb None Specifies the thumbnail indicator. It will be inserted just before the file extension, so mypic.jpg would become mypic_thumb.jpg R
maintain_ratio TRUE TRUE/FALSE (boolean) Specifies whether to maintain the original aspect ratio when resizing or use hard values. R, C
master_dim auto auto, width, height Specifies what to use as the master axis when resizing or creating thumbs. For example, let's say you want to resize an image to 100 X 75 pixels. If the source image size does not allow perfect resizing to those dimensions, this setting determines which axis should be used as the hard value. "auto" sets the axis automatically based on whether the image is taller then wider, or vice versa. R
rotation_angle None 90, 180, 270, vrt, hor Specifies the angle of rotation when rotating images. Note that PHP rotates counter-clockwise, so a 90 degree rotation to the right must be specified as 270. X
x_axis None None Sets the X coordinate in pixels for image cropping. For example, a setting of 30 will crop an image 30 pixels from the left. C
y_axis None None Sets the Y coordinate in pixels for image cropping. For example, a setting of 30 will crop an image 30 pixels from the top. C

Setting preferences in a config file

If you prefer not to set preferences using the above method, you can instead put them into a config file. Simply create a new file called image_lib.php, add the $config array in that file. Then save the file in: config/image_lib.php and it will be used automatically. You will NOT need to use the $this->image_lib->initialize function if you save your preferences in a config file.

$this->image_lib->resize()

The image resizing function lets you resize the original image, create a copy (with or without resizing), or create a thumbnail image.

For practical purposes there is no difference between creating a copy and creating a thumbnail except a thumb will have the thumbnail marker as part of the name (ie, mypic_thumb.jpg).

All preferences listed in the table above are available for this function except these three: rotation_angle, x_axis, and y_axis.

Creating a Thumbnail

The resizing function will create a thumbnail file (and preserve the original) if you set this preference to TRUE:

$config['create_thumb'] = TRUE;

This single preference determines whether a thumbnail is created or not.

Creating a Copy

The resizing function will create a copy of the image file (and preserve the original) if you set a path and/or a new filename using this preference:

$config['new_image'] = '/path/to/new_image.jpg';

Notes regarding this preference:

  • If only the new image name is specified it will be placed in the same folder as the original
  • If only the path is specified, the new image will be placed in the destination with the same name as the original.
  • If both the path and image name are specified it will placed in its own destination and given the new name.

Resizing the Original Image

If neither of the two preferences listed above (create_thumb, and new_image) are used, the resizing function will instead target the original image for processing.

$this->image_lib->crop()

The cropping function works nearly identically to the resizing function except it requires that you set preferences for the X and Y axis (in pixels) specifying where to crop, like this:

$config['x_axis'] = '100';
$config['y_axis'] = '40';

All preferences listed in the table above are available for this function except these: rotation_angle, width, height, create_thumb, new_image.

Here's an example showing how you might crop an image:

$config['image_library'] = 'imagemagick';
$config['library_path'] = '/usr/X11R6/bin/';
$config['source_image'] = '/path/to/image/mypic.jpg';
$config['x_axis'] = '100';
$config['y_axis'] = '60';

$this->image_lib->initialize($config);

if ( ! $this->image_lib->crop())
{
    echo $this->image_lib->display_errors();
}

Note: Without a visual interface it is difficult to crop images, so this function is not very useful unless you intend to build such an interface. That's exactly what we did using for the photo gallery module in ExpressionEngine, the CMS we develop. We added a JavaScript UI that lets the cropping area be selected.

$this->image_lib->rotate()

The image rotation function requires that the angle of rotation be set via its preference:

$config['rotation_angle'] = '90';

There are 5 rotation options:

  1. 90 - rotates counter-clockwise by 90 degrees.
  2. 180 - rotates counter-clockwise by 180 degrees.
  3. 270 - rotates counter-clockwise by 270 degrees.
  4. hor - flips the image horizontally.
  5. vrt - flips the image vertically.

Here's an example showing how you might rotate an image:

$config['image_library'] = 'netpbm';
$config['library_path'] = '/usr/bin/';
$config['source_image'] = '/path/to/image/mypic.jpg';
$config['rotation_angle'] = 'hor';

$this->image_lib->initialize($config);

if ( ! $this->image_lib->rotate())
{
    echo $this->image_lib->display_errors();
}

$this->image_lib->clear()

The clear function resets all of the values used when processing an image. You will want to call this if you are processing images in a loop.

$this->image_lib->clear();

 

Image Watermarking

The Watermarking feature requires the GD/GD2 library.

Two Types of Watermarking

There are two types of watermarking that you can use:

  • Text: The watermark message will be generating using text, either with a True Type font that you specify, or using the native text output that the GD library supports. If you use the True Type version your GD installation must be compiled with True Type support (most are, but not all).
  • Overlay: The watermark message will be generated by overlaying an image (usually a transparent PNG or GIF) containing your watermark over the source image.

Watermarking an Image

Just as with the other functions (resizing, cropping, and rotating) the general process for watermarking involves setting the preferences corresponding to the action you intend to perform, then calling the watermark function. Here is an example:

$config['source_image'] = '/path/to/image/mypic.jpg';
$config['wm_text'] = 'Copyright 2006 - John Doe';
$config['wm_type'] = 'text';
$config['wm_font_path'] = './system/fonts/texb.ttf';
$config['wm_font_size'] = '16';
$config['wm_font_color'] = 'ffffff';
$config['wm_vrt_alignment'] = 'bottom';
$config['wm_hor_alignment'] = 'center';
$config['wm_padding'] = '20';

$this->image_lib->initialize($config);

$this->image_lib->watermark();

The above example will use a 16 pixel True Type font to create the text "Copyright 2006 - John Doe". The watermark will be positioned at the bottom/center of the image, 20 pixels from the bottom of the image.

Note: In order for the image class to be allowed to do any processing, the image file must have "write" file permissions. For example, 777.

Watermarking Preferences

This table shown the preferences that are available for both types of watermarking (text or overlay)

PreferenceDefault ValueOptionsDescription
wm_type text text, overlay Sets the type of watermarking that should be used.
source_image None None Sets the source image name/path. The path must be a relative or absolute server path, not a URL.
dynamic_output FALSE TRUE/FALSE (boolean) Determines whether the new image file should be written to disk or generated dynamically. Note: If you choose the dynamic setting, only one image can be shown at a time, and it can't be positioned on the page. It simply outputs the raw image dynamically to your browser, along with image headers.
quality 90% 1 - 100% Sets the quality of the image. The higher the quality the larger the file size.
padding None A number The amount of padding, set in pixels, that will be applied to the watermark to set it away from the edge of your images.
wm_vrt_alignment bottom top, middle, bottom Sets the vertical alignment for the watermark image.
wm_hor_alignment center left, center, right Sets the horizontal alignment for the watermark image.
wm_hor_offset None None You may specify a horizontal offset (in pixels) to apply to the watermark position. The offset normally moves the watermark to the right, except if you have your alignment set to "right" then your offset value will move the watermark toward the left of the image.
wm_vrt_offset None None You may specify a vertical offset (in pixels) to apply to the watermark position. The offset normally moves the watermark down, except if you have your alignment set to "bottom" then your offset value will move the watermark toward the top of the image.

Text Preferences

This table shown the preferences that are available for the text type of watermarking.

PreferenceDefault ValueOptionsDescription
wm_text None None The text you would like shown as the watermark. Typically this will be a copyright notice.
wm_font_path None None The server path to the True Type Font you would like to use. If you do not use this option, the native GD font will be used.
wm_font_size 16 None The size of the text. Note: If you are not using the True Type option above, the number is set using a range of 1 - 5. Otherwise, you can use any valid pixel size for the font you're using.
wm_font_color ffffff None The font color, specified in hex. Note, you must use the full 6 character hex value (ie, 993300), rather than the three character abbreviated version (ie fff).
wm_shadow_color None None The color of the drop shadow, specified in hex. If you leave this blank a drop shadow will not be used. Note, you must use the full 6 character hex value (ie, 993300), rather than the three character abbreviated version (ie fff).
wm_shadow_distance 3 None The distance (in pixels) from the font that the drop shadow should appear.

Overlay Preferences

This table shown the preferences that are available for the overlay type of watermarking.

PreferenceDefault ValueOptionsDescription
wm_overlay_path None None The server path to the image you wish to use as your watermark. Required only if you are using the overlay method.
wm_opacity 50 1 - 100 Image opacity. You may specify the opacity (i.e. transparency) of your watermark image. This allows the watermark to be faint and not completely obscure the details from the original image behind it. A 50% opacity is typical.
wm_x_transp 4 A number If your watermark image is a PNG or GIF image, you may specify a color on the image to be "transparent". This setting (along with the next) will allow you to specify that color. This works by specifying the "X" and "Y" coordinate pixel (measured from the upper left) within the image that corresponds to a pixel representative of the color you want to be transparent.
wm_y_transp 4 A number Along with the previous setting, this allows you to specify the coordinate to a pixel representative of the color you want to be transparent.