Image::JpegMinimal

2022-05-23 09:16| 来源: 网络整理| 查看: 265

NAME SYNOPSIS DESCRIPTION METHODS Image::JpegMinimal->new( %OPTIONS ) $compressor->data_preview $compressor->headers HTML JAVASCRIPT REPOSITORY SUPPORT BUG TRACKER AUTHOR COPYRIGHT (c) LICENSE NAME

Image::JpegMinimal - create JPEG previews without headers

SYNOPSIS my $compressor = Image::JpegMinimal->new( xmax => 42, ymax => 42, jpegquality => 20, ); sub gen_img { my @tags; for my $file (@_) { my $imager = Imager->new( file => $file ); my $preview = $compressor->data_preview( $file ); my ($w, $h ) = ($imager->getwidth,$imager->getheight); my $html = Image::JpegMinimal->new( %OPTIONS ) my $compressor = Image::JpegMinimal->new( xmax => 42, ymax => 42, jpegquality => 20, );

Creates a new compressor object. The xmax and ymax values give the maximum dimensions for the size of the preview image. It is suggested that the preview image is heavily blurred when presenting the preview image to the user to hide the JPEG artifacts.

$compressor->data_preview my $data_preview = $compressor->data_preview( $file );

Reads the JPEG data from a file and returns a base64 encoded string of the reduced image data. You stuff this into the data-preview attribute of the img tag in your HTML.

$compressor->headers my %headers = $compressor->headers;

After processing all files, this method returns the headers that are common to the images. You need to pass this to your Javascript.

HTML

Each image that has a pre-preview placeholder will need to store the placeholder data in the data-preview attribute. That is all the modification you need. You should also set the width and height attributes of the image so that no ugly image-popping occurs when the real data arrives. The $payload64 is the data that is returned from the ->data_preview call.

JAVASCRIPT

You will need to include some Javascript like the following in your page, preferrably near the end so the code runs right after the HTML has loaded completely but image loading has not yet fired.

The hash %headers should be set to the base64 encoded fixed headers as returned by the ->headers( $file ) call. The image HTML should have been constructed as outlined above.

"use strict"; var header = { l : atob("$headers{l}"), h : atob("$headers{p}"), }; function reconstruct(data) { // Reconstruct a JPEG header from our special data structure var raw = atob(data); // Keep as "char" so we don't have to bother with Unicode vs. ASCII var width = raw.charAt(0); var height = raw.charAt(1); var payload = raw.substring(2,raw.length); var head; if( width < height ) { head = header["p"] } else { head = header["l"] }; var dimension_patch = width+height; var patched_header = head.substring(0,head.length-13) + width + head.substring(head.length-12,head.length-11) + height + head.substring(head.length-10,head.length); var reconstructed = patched_header+payload; var encoded = "data:image/jpeg;base64,"+btoa(reconstructed); return encoded; } var image_it = document.evaluate("//img[\@data-preview]",document, null, XPathResult.ANY_TYPE, null); var images = []; var el = image_it.iterateNext(); while( el ) { images.push(el); el = image_it.iterateNext(); }; for( var i = 0; i < images.length; i++ ) { var el = images[ i ]; if( !el.complete || el.naturalWidth == 0 || el.naturalHeight == 0) { var fullsrc = el.src; var loadsrc = reconstruct( el.getAttribute("data-preview")); var container = document.createElement('div'); container.style.overflow = "hidden"; container.style.display = "inline"; container.style.position = "relative"; var parent = el.parentNode; parent.insertBefore(container, el); container.appendChild(el); // Set up the placeholder data el.src = loadsrc; el.style.filter = "blur(8px)"; var img = document.createElement('img'); img.width = el.width; img.height = el.height; // Shouldn't we also copy the style and maybe even some events?! // img = el.cloneNode(true); // except this doesn't copy the eventListeners etc. Duh. (function(img,container,src) { img.onload = function() { // Put the loaded child in the place of the preloaded data parent.replaceChild(img,container); }; var timeout = 1000+Math.random()*3000; // Kick off the loading // The timeout is just for demonstration purposes // window.setTimeout(function() { img.src = src; //}, timeout); }(img,container,fullsrc)); } else { // Image has already been loaded (from cache), nothing to do here }; }; REPOSITORY

The public repository of this module is http://github.com/Corion/image-jpegminimal.

SUPPORT

The public support forum of this module is https://perlmonks.org/.

BUG TRACKER

Please report bugs in this module via the RT CPAN bug queue at https://rt.cpan.org/Public/Dist/Display.html?Name=Image-JpegMinimal or via mail to [email protected].

AUTHOR

Max Maischein [email protected]

LICENSE

This module is released under the same terms as Perl itself.

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