我有一个PHP图像上传系统，允许用户上传各种图像（JPG，GIF，PNG）。上传的每张图片都有一个图标（20x20），缩略图（150x150）和为其生成的明信片（500x500） - 我称之为“元图像”。如果原始图像尺寸不像元图像那样是方形的，则将其缩放到最佳拟合，并且以适当的尺寸生成透明画布，并将元图像放置在其上。由于这种透明的画布，以及其他目的，所有生成的元图像本身都是PNG（无论原始图像格式如何）。
例如，如果用户上传800px x 600px JPG图像，则文件系统中会出现以下内容：
这适用于JPG和GIF文件 - 所有颜色都处理得正确，尺寸有效等等。
但是，如果我上传其中有黑色的PNG（rgb（0,0,0），＃000000），则生成的3个元图像全部变为透明黑色。其他一切都很好 - 尺寸等等。请记住，透明GIF似乎工作正常，即使内部有黑色。
有人可以向我解释如何解决这个问题吗？下面是我为这个系统编写的代码（注意在它下面定义了抽象类的3个扩展）：
<?php
/*
* TODO: There is no reason for this class to be abstract except that I have not
* added any of the setters/getters/etc which would make it useful on its
* own. As is, an instantiation of this class would not accomplish
* anything so I have made it abstract to avoid instantiation. Three
* simple and usable extensions of this class exist below it in this file.
*/
abstract class ObjectImageRenderer
{
const WRITE_DIR = SITE_UPLOAD_LOCATION;
protected $iTargetWidth = 0;
protected $iTargetHeight = 0;
protected $iSourceWidth = 0;
protected $iSourceHeight = 0;
protected $iCalculatedWidth = 0;
protected $iCalculatedHeight = 0;
protected $sSourceLocation = '';
protected $sSourceExt = '';
protected $oSourceImage = null;
protected $sTargetLocation = '';
protected $sTargetNamePrefix = '';
protected $oTargetImage = null;
protected $oTransparentCanvas = null;
protected $bNeedsCanvas = false;
protected $bIsRendered = false;
public function __construct( $sSourceLocation )
{
if( ! is_string( $sSourceLocation ) || $sSourceLocation === '' ||
! is_file( $sSourceLocation ) || ! is_readable( $sSourceLocation )
)
{
throw new Exception( __CLASS__ . ' must be instantiated with valid path/filename of source image as first param.' );
}
$this->sSourceLocation = $sSourceLocation;
$this->resolveNames();
}
public static function factory( $sSourceLocation, $size )
{
switch( $size )
{
case 'icon':
return new ObjectIconRenderer( $sSourceLocation );
break;
case 'thumbnail':
return new ObjectThumbnailRenderer( $sSourceLocation );
break;
case 'postcard':
return new ObjectPostcardRenderer( $sSourceLocation );
break;
}
}
public static function batchRender( $Source )
{
if( is_string( $Source ) )
{
try
{
ObjectImageRenderer::factory( $Source, 'icon' )->render();
ObjectImageRenderer::factory( $Source, 'thumbnail' )->render();
ObjectImageRenderer::factory( $Source, 'postcard' )->render();
}
catch( Exception $exc )
{
LogProcessor::submit( 500, $exc->getMessage() );
}
}
else if( is_array( $Source ) && count( $Source ) > 0 )
{
foreach( $Source as $sSourceLocation )
{
if( is_string( $sSourceLocation ) )
{
self::batchRender( $sSourceLocation );
}
}
}
}
/**
* loadImageGD - read image from filesystem into GD based image resource
*
* @access public
* @static
* @param STRING $sImageFilePath
* @param STRING $sSourceExt OPTIONAL
* @return RESOURCE
*/
public static function loadImageGD( $sImageFilePath, $sSourceExt = null )
{
$oSourceImage = null;
if( is_string( $sImageFilePath ) && $sImageFilePath !== '' &&
is_file( $sImageFilePath ) && is_readable( $sImageFilePath )
)
{
if( $sSourceExt === null )
{
$aPathInfo = pathinfo( $sImageFilePath );
$sSourceExt = strtolower( (string) $aPathInfo['extension'] );
}
switch( $sSourceExt )
{
case 'jpg':
case 'jpeg':
case 'pjpeg':
$oSourceImage = imagecreatefromjpeg( $sImageFilePath );
break;
case 'gif':
$oSourceImage = imagecreatefromgif( $sImageFilePath );
break;
case 'png':
case 'x-png':
$oSourceImage = imagecreatefrompng( $sImageFilePath );
break;
default:
break;
}
}
return $oSourceImage;
}
protected function resolveNames()
{
$aPathInfo = pathinfo( $this->sSourceLocation );
$this->sSourceExt = strtolower( (string) $aPathInfo['extension'] );
$this->sTargetLocation = self::WRITE_DIR . $this->sTargetNamePrefix . $aPathInfo['basename'] . '.png';
}
protected function readSourceFileInfo()
{
$this->oSourceImage = self::loadImageGD( $this->sSourceLocation, $this->sSourceExt );
if( ! is_resource( $this->oSourceImage ) )
{
throw new Exception( __METHOD__ . ': image read failed for ' . $this->sSourceLocation );
}
$this->iSourceWidth = imagesx( $this->oSourceImage );
$this->iSourceHeight = imagesy( $this->oSourceImage );
return $this;
}
protected function calculateNewDimensions()
{
if( $this->iSourceWidth === 0 || $this->iSourceHeight === 0 )
{
throw new Exception( __METHOD__ . ': source height or width is 0. Has ' . __CLASS__ . '::readSourceFileInfo() been called?' );
}
if( $this->iSourceWidth > $this->iTargetWidth || $this->iSourceHeight > $this->iTargetHeight )
{
$nDimensionRatio = ( $this->iSourceWidth / $this->iSourceHeight );
if( $nDimensionRatio > 1 )
{
$this->iCalculatedWidth = $this->iTargetWidth;
$this->iCalculatedHeight = (int) round( $this->iTargetWidth / $nDimensionRatio );
}
else
{
$this->iCalculatedWidth = (int) round( $this->iTargetHeight * $nDimensionRatio );
$this->iCalculatedHeight = $this->iTargetHeight;
}
}
else
{
$this->iCalculatedWidth = $this->iSourceWidth;
$this->iCalculatedHeight = $this->iSourceHeight;
}
if( $this->iCalculatedWidth < $this->iTargetWidth || $this->iCalculatedHeight < $this->iTargetHeight )
{
$this->bNeedsCanvas = true;
}
return $this;
}
protected function createTarget()
{
if( $this->iCalculatedWidth === 0 || $this->iCalculatedHeight === 0 )
{
throw new Exception( __METHOD__ . ': calculated height or width is 0. Has ' . __CLASS__ . '::calculateNewDimensions() been called?' );
}
$this->oTargetImage = imagecreatetruecolor( $this->iCalculatedWidth, $this->iCalculatedHeight );
$aTransparentTypes = Array( 'gif', 'png', 'x-png' );
if( in_array( $this->sSourceExt, $aTransparentTypes ) )
{
$oTransparentColor = imagecolorallocate( $this->oTargetImage, 0, 0, 0 );
imagecolortransparent( $this->oTargetImage, $oTransparentColor);
imagealphablending( $this->oTargetImage, false );
}
return $this;
}
protected function fitToMaxDimensions()
{
$iTargetX = (int) round( ( $this->iTargetWidth - $this->iCalculatedWidth ) / 2 );
$iTargetY = (int) round( ( $this->iTargetHeight - $this->iCalculatedHeight ) / 2 );
$this->oTransparentCanvas = imagecreatetruecolor( $this->iTargetWidth, $this->iTargetHeight );
imagealphablending( $this->oTransparentCanvas, false );
imagesavealpha( $this->oTransparentCanvas, true );
$oTransparentColor = imagecolorallocatealpha( $this->oTransparentCanvas, 0, 0, 0, 127 );
imagefill($this->oTransparentCanvas, 0, 0, $oTransparentColor );
$bReturnValue = imagecopyresampled( $this->oTransparentCanvas, $this->oTargetImage, $iTargetX, $iTargetY, 0, 0, $this->iCalculatedWidth, $this->iCalculatedHeight, $this->iCalculatedWidth, $this->iCalculatedHeight );
$this->oTargetImage = $this->oTransparentCanvas;
return $bReturnValue;
}
public function render()
{
/*
* TODO: If this base class is ever made instantiable, some re-working is
* needed such that the developer harnessing it can choose whether to
* write to the filesystem on render, he can ask for the
* image resources, determine whether cleanup needs to happen, etc.
*/
$this
->readSourceFileInfo()
->calculateNewDimensions()
->createTarget();
$this->bIsRendered = imagecopyresampled( $this->oTargetImage, $this->oSourceImage, 0, 0, 0, 0, $this->iCalculatedWidth, $this->iCalculatedHeight, $this->iSourceWidth, $this->iSourceHeight );
if( $this->bIsRendered && $this->bNeedsCanvas )
{
$this->bIsRendered = $this->fitToMaxDimensions();
}
if( $this->bIsRendered )
{
imagepng( $this->oTargetImage, $this->sTargetLocation );
@chmod( $this->sTargetLocation, 0644 );
}
if( ! $this->bIsRendered )
{
throw new Exception( __METHOD__ . ': failed to copy image' );
}
$this->cleanUp();
}
public function cleanUp()
{
if( is_resource( $this->oSourceImage ) )
{
imagedestroy( $this->oSourceImage );
}
if( is_resource( $this->oTargetImage ) )
{
imagedestroy( $this->oTargetImage );
}
if( is_resource( $this->oTransparentCanvas ) )
{
imagedestroy( $this->oTransparentCanvas );
}
}
}
class ObjectIconRenderer extends ObjectImageRenderer
{
public function __construct( $sSourceLocation )
{
/* These Height/Width values are also coded in
* src/php/reference/display/IconUploadHandler.inc
* so if you edit them here, do it there too
*/
$this->iTargetWidth = 20;
$this->iTargetHeight = 20;
$this->sTargetNamePrefix = 'icon_';
parent::__construct( $sSourceLocation );
}
}
class ObjectThumbnailRenderer extends ObjectImageRenderer
{
public function __construct( $sSourceLocation )
{
/* These Height/Width values are also coded in
* src/php/reference/display/IconUploadHandler.inc
* so if you edit them here, do it there too
*/
$this->iTargetWidth = 150;
$this->iTargetHeight = 150;
$this->sTargetNamePrefix = 'thumbnail_';
parent::__construct( $sSourceLocation );
}
}
class ObjectPostcardRenderer extends ObjectImageRenderer
{
public function __construct( $sSourceLocation )
{
/* These Height/Width values are also coded in
* src/php/reference/display/IconUploadHandler.inc
* so if you edit them here, do it there too
*/
$this->iTargetWidth = 500;
$this->iTargetHeight = 500;
$this->sTargetNamePrefix = 'postcard_';
parent::__construct( $sSourceLocation );
}
}
我用来运行它的代码是：
<?php
ObjectImageRenderer::batchRender( $sSourceFile );
主要问题似乎出现在createTarget()和fitToMaxDimensions()方法中。在createTarget()中，如果我注释掉以下几行：
$aTransparentTypes = Array( 'gif', 'png', 'x-png' );
if( in_array( $this->sSourceExt, $aTransparentTypes ) )
{
$oTransparentColor = imagecolorallocate( $this->oTargetImage, 0, 0, 0 );
imagecolortransparent( $this->oTargetImage, $oTransparentColor);
imagealphablending( $this->oTargetImage, false );
}
我不再失去黑色，但所有现有的透明度都会变黑。
我认为问题在于我使用黑色作为透明度通道。但是，如何避免使用图像中的颜色作为透明度通道？
感谢任何能帮助我理解透明背后的奥秘的人！
吉姆
答案 0 :(得分：1)
你明确指出0,0,0是透明的：
$oTransparentColor = imagecolorallocatealpha( $this->oTransparentCanvas, 0, 0, 0, 127 );
这将适用于图像中颜色三联体为0,0,0的所有像素 - 换句话说，所有黑色，正如您所发现的那样。
如果您希望原始图像通过，您将转换为使用Alpha通道。它是图像中的单独“层”，专门为每个像素指定透明度/不透明度。那或扫描图像中的原始颜色未使用的颜色，然后将其指定为新的透明值而不是默认为0,0,0。