Error Level Analysis with Imagick PHP - result without color

Question

yesterday I posted about a problem with recreating an Error Level Analysis in PHP with Imagmagick. In this question I found a solution with the command-line interaction and tried to translate it into Imagick and PHP.

The following code was proposed:

convert barn.jpg \( +clone -quality 95 \) -compose difference -composite -auto-level -gamma 1.5 barn_ela.png

In this example, the result should highlight the manipulated parts of the image. So I implemented the following code:

            $ELAImageMagick = new Imagick($targetDir . $OriginalImage);
            $OriginalImageMagick = new Imagick($targetDir . $OriginalImage);

            $ELAImageMagick->setImageCompression(Imagick::COMPRESSION_JPEG);
            $ELAImageMagick->setImageCompressionQuality($this->getRequest()->postVar('elaQuality'));

            $ELAImageMagick->compositeImage($OriginalImageMagick, Imagick::COMPOSITE_DIFFERENCE, 1,1);

            $ELAImageMagick->autoLevelImage();

            //Set gamma with a slider in the frontend
            $ELAImageMagick->gammaImage($this->getRequest()->postVar('elaSize'));

            //save ELA-image into Folder
            $ELAImageMagick->writeImage($targetDir . $ELAImage);

Unfortunatly the result does not come close to the desired optic of the result:

The original image (yellow bird has been added in photoshop)

The ELA-Result

Does anyone have an idea, what step I didn't catch quite right and how to solve it? I looked into the documentation and didn't really find any alternatives to this.

Thanks in advance!

Answer 1

You need to first prove that your code works in Imagemagick. But -quality only works for writing a JPG output. So you need to actually save the result of the -quality operation as a JPG and then use it in a second command. Here I just pipe from one convert to another. The first convert actually creates the compressed JPG but just passes it to the second command without writing to disk.

Input:

convert birds.jpg -quality 95 JPG:- | convert birds.jpg - -compose difference -composite -auto-level -gamma 1.5 birds_ela.png

The result I get is:

This is a JPG version of the PNG output since the PNG was too large to post.

However the results from the command line do not match the resulting image you show. So the command is not going to work in Imagick either.

ADDITION:

From what I can see there is no tampering other than possibly the orange bird in the middle. Most of the image is flat or has random noise. The small bird in the middle has a bit brighter texture and so may be an insert.

ADDITION 2

For enhancing edge artifacts, add -geometry +1+1 to my command above just before -compose difference.

convert birds.jpg -quality 95 JPG:- | convert birds.jpg - -geometry +1+1 -compose difference -composite -auto-level -gamma 2 -define jpeg:extent=2000kb birds_ela2.png

Again posting a JPG version for file size issues.

This looks similar to your posted result.