Convert images from RGB to CMYK using Imagick

Question

I am trying to convert RGB images to CMYK because they need to be printed. I am using this code:

<?php $filePath = 'rgb.jpg'; // First save image as png $image = new Imagick($filePath); $image->setImageCompression(Imagick::COMPRESSION_UNDEFINED); $image->setImageCompressionQuality(0); $image->setImageFormat("png"); $filePath = 'rgb.png'; $image->writeImage($filePath); $image->clear(); $image->destroy(); $image = null; // Convert colors $image = new Imagick($filePath); $image->stripImage(); $image->setImageColorspace(Imagick::COLORSPACE_CMYK); $image->setImageCompression(Imagick::COMPRESSION_UNDEFINED); $image->setImageCompressionQuality(0); $image->setImageFormat("png"); $filePath = 'cmyk.png'; $image->writeImage($filePath); $image->clear(); $image->destroy(); $image = null; $fileUrl = 'http://www.product-designer.nl/rgb2cmyk/cmyk.png'; ?> CMYK Image:<br/> <img src="<?php echo $fileUrl; ?>" width="400" /><br /><br /> <?php $fileUrl = 'http://www.product-designer.nl/rgb2cmyk/rgb.png'; ?> RGB Image:<br/> <img src="<?php echo $fileUrl ?>" width="400" /> 

You can see the result at http://product-designer.nl/rgb2cmyk I don't know how, but somehow the colors in the image are upside down. I need to convert the image, but the colors should be as close as possible to the RGB colors.

Does anyone know how to do this?

thanks

Answer 1

Take a look here :

 <?php // don't use this (it inverts the image) // $img->setImageColorspace (imagick::COLORSPACE_RGB); if ($img->getImageColorspace() == Imagick::COLORSPACE_CMYK) { $profiles = $img->getImageProfiles('*', false); // we're only interested if ICC profile(s) exist $has_icc_profile = (array_search('icc', $profiles) !== false); // if it doesnt have a CMYK ICC profile, we add one if ($has_icc_profile === false) { $icc_cmyk = file_get_contents(dirname(__FILE__).'/USWebUncoated.icc'); $img->profileImage('icc', $icc_cmyk); unset($icc_cmyk); } // then we add an RGB profile $icc_rgb = file_get_contents(dirname(__FILE__).'/sRGB_v4_ICC_preference.icc'); $img->profileImage('icc', $icc_rgb); unset($icc_rgb); } $img->stripImage (); // this will drop down the size of the image dramatically (removes all profiles) ?> 

Answer 2

Good, so this is a difficult problem. I had the same problem and it took me days to solve this problem. You need negateImage (), please see my example and make sure that you only do this for php 5.3.x, as this problem is unique to this php vs.

 $range = $jpeg->getQuantumRange(); $php_vs_arr = preg_split("/\./", phpversion()); $php_vs = $php_vs_arr[0] . '.' . $php_vs_arr[1]; if ($jpeg->getImageColorspace() == Imagick::COLORSPACE_CMYK) { //make sure cmyk color-space is set correctly $jpeg->setImageColorspace(12); // then we add an RGB profile $icc_rgb = file_get_contents(FRAMEWORK_PATH . DS . 'color' . DS . 'AdobeRGB1998.icc'); $jpeg->profileImage('icc', $icc_rgb); unset($icc_rgb); //set color space to rgb $jpeg->setImageColorspace(13); //fix gamma, hue, saturation, brightness if($php_vs < 5.3) { //ADJUST GAMMA BY 2.0 for 5.2.x $jpeg->levelImage(0, 2.0, $range['quantumRangeString']); } else { //php 5.3 hack FOR INVERTED COLORS $jpeg->negateImage(false, Imagick::CHANNEL_ALL); } } $jpeg->stripImage(); 

Note: my Imagick object is obviously $ jpeg

In addition, you will need to download the AdobeRGB1998.icc profile from the Adobe website, just search on Google.

I hope this helps, please mark this as the correct answer, as many people have problems with this.

Answer 3

A possible reason is that RGB is an additive color scheme and CMYK is a subtractive color scheme. That is, we can convert RGB to CMYK using the following formulas:

 C = 255 - R; M = 255 - G; Y = 255 - B; 

It seems like "how to invert colors." Therefore, in this case, we must also determine the value of K.

To avoid this, we can use ICC profiles .

One possible solution:

 $image = new Imagick('img/test.jpg'); $profiles = $image->getImageProfiles('*', false); if (!array_search('icc', $profiles)) { // Without this code Photoshop cannot open image with original icc-profile $icc_rgb = file_get_contents('profiles/AppleRGB.icc'); if ($image->profileImage('icc', $icc_rgb)) echo '<br>Changed!'; unset($icc_rgb); } // don't use this code, it leads to inverted image //$image->setImageColorspace(Imagick::COLORSPACE_CMYK); // tiff format supports CMYK colorscheme $image->setFormat('tiff'); $image->setImageCompression(Imagick::COMPRESSION_UNDEFINED); $image->setImageCompressionQuality(0); // We can download profiles here http://www.adobe.com/support/downloads/thankyou.jsp?ftpID=4075&fileID=3790 $icc_cmyk_profile_path='profiles/USWebCoatedSWOP.icc'; $icc_cmyk = file_get_contents($icc_cmyk_profile_path); if ($image->profileImage('icc', $icc_cmyk)) echo '<br>Changed!'; unset($icc_cmyk); // Drops all profiles, so we comment it //$image->stripImage(); if ($image->writeImage('img/test_cmyk.tiff')) echo '<br>Save!'; $image->clear(); $image->destroy(); 

Changes the file size, for example. 72 KB to 1.4 MB