imagetruecolortopalette

(PHP 4 >= 4.0.6, PHP 5)

imagetruecolortopalette — Converte uma imagem true color para uma imagem de paleta

Descrição

bool imagetruecolortopalette ( resource $image , bool $dither , int $ncolors )

imagetruecolortopalette() converte uma imagem truecolor para uma imagem de paleta. O código para esta função foi escrito originalmente pelo Independent JPEG Group library code, o qual é excelente. O código foi modificado para preservar tanta informação do alpha channel quanto possível na paleta de resultado, em adição a preservar as cores tão bem quanto possível. Isto não funciona tão bem quanto podia ser esperado. Normalmente é melhor simplesmente produzir e enviar uma imagem truecolor, a qual tem garantidamente uma qualidade de saída melhor.

Parâmetros

image: An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
dither: dither indica se a imagem deve ser estremecida - se ele é TRUE então o estremecimento será usado, o que resulta em uma imagem mais manchada mas com melhor aproximação da cor.
ncolors: Define o número máximo de cores que devem ser retidos na paleta.

Valor Retornado

Retorna TRUE em caso de sucesso ou FALSE em falhas.

Notas

Nota: Esta função precisa do GD 2.0.1 ou posterior (2.0.28 ou posterior é recomendado).

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Last updated: Fri, 13 Nov 2009

add a note User Contributed Notes
imagetruecolortopalette

djcassis(a)gmail.com
21-Sep-2008 11:52


>> zmorris at zsculpt dot com



I don't have the imageColorMatch() function on my server, but I could slighty improve the quality of the GIF/PNG image by converting it first to 256 colors, then to true colors and finally to the desired number of colors.



<?php



$dither = true;

$colors = 64;



$tmp = imageCreateFromJpeg('example.jpg');

$width = imagesX($tmp);

$height = imagesY($tmp);

imageTrueColorToPalette($tmp, $dither, 256);

$image = imageCreateTrueColor($width, $height);

imageCopy($image, $tmp, 0, 0, 0, 0, $width, $height);

imageDestroy($tmp);

imageTrueColorToPalette($image, $dither, $colors);



?>



Final $image will still have less than 64 colors, but more than if it was directly converted to 64 colors, and they match the JPEG image more.



Dunno why true colors to palette conversions are such a problem...

burninleo at gmx dot net
28-May-2006 02:51


If You know which palette to use (e.g. 255 colors greyscale) You may achieve better results using the following way:



1. Create new image

2. Apply palette

3. imagecopy() the content



This is especially helpful if you created a greyscale picture in trucolor-mode (to use antialiasing for example) but need to send it as palette (to use transparency in Internet Explorer).



The following example will *not* create great results from "real" truecolor images but works well on grey truecolor images:



<?PHP

function imageTruecolorToGrayscale(&$image) {

    $copy = $image;

    $dx = imagesx($image);

    $dy = imagesy($image);

    $image = imagecreate($dx, $dy);

    

    // 254 Colors + 1 reserved for transparency

    $transparency = imagecolorallocate($image, 0, 255, 0);

    $max = 255; $dd = 254;

    for ($i=0; $i<$dd; $i++) {

        $val = round($max * $i / ($dd-1));

        imagecolorallocate($image, $val, $val, $val);

    }

    

    imagecopy($image, $copy, 0, 0, 0, 0, $dx, $dy);

    imagedestroy($copy);

    return $transparency;

}

?>

will at fnatic dot com
24-Feb-2006 06:49


a basic palette to true color function

<?php

    function imagepalettetotruecolor(&$img)

    {

        if (!imageistruecolor($img))

        {

            $w = imagesx($img);

            $h = imagesy($img);

            $img1 = imagecreatetruecolor($w,$h);

            imagecopy($img1,$img,0,0,0,0,$w,$h);

            $img = $img1;

        }

    }

?>

zmorris at zsculpt dot com
17-Aug-2004 03:58


Sometimes this function gives ugly/dull colors (especially when ncolors < 256).  Here is a replacement that uses a temporary image and ImageColorMatch() to match the colors more accurately.  It might be a hair slower, but the file size ends up the same:



<?php

function    ImageTrueColorToPalette2( $image, $dither, $ncolors )

{

    $width = imagesx( $image );

    $height = imagesy( $image );

    $colors_handle = ImageCreateTrueColor( $width, $height );

    ImageCopyMerge( $colors_handle, $image, 0, 0, 0, 0, $width, $height, 100 );

    ImageTrueColorToPalette( $image, $dither, $ncolors );

    ImageColorMatch( $colors_handle, $image );

    ImageDestroy( $colors_handle );

}

?>

php at roelvanmastbergen dot nl
06-Jun-2004 02:34


The palette created by this function often looks quite awful (at least it did on all of my test images). A better way to convert your true-colour images is by first making a resized copy of them with imagecopyresampled() to a 16x16 pixel destination. The resized image then contains only 256 pixels, which is exactly the number of colours you need. These colours usually look a lot better than the ones generated by imagetruecolortopalette().



The only disadvantage to this method I have found is that different-coloured details in the original image are lost in the conversion.

jemore at nospaM dot m6net dot fr
22-Nov-2003 04:25


If you open a truecolor image (with imageCreateFromPng for example), and you save it directly to GIF format with imagegif, you can have a 500 internal server error. You must use imageTrueColorToPalette to reduce to 256 colors before saving the image in GIF format.

darkelder at php dot net
17-Jul-2003 06:34


TrueColor images should be converted to Palette images with this function. So, if you want to use imagecolorstotal() function [ http://php.net/manual/en/function.imagecolorstotal.php ] , you should first convert the image to a palette image with imagetruecolortopalette();

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Last updated: Fri, 13 Nov 2009