Does 3.8.0 version lack support for some metrics (SSIM, DSSIM, PHASH and others)?

[mikenosp]

Using latest MAMP with PHP 8.3.28, imagick 3.8.0 enabled. phpinfo reports "Imagick compiled with ImageMagick version 7.1.0-23 Q16-HDRI x86_64 2022-02-05" and "Imagick using ImageMagick library version 7.1.0-23 Q16-HDRI x86_64 2022-02-05". However, any attempt to use Imagick::METRIC_SSIM continues to fail with "Uncaught Error: Undefined constant Imagick::METRIC_SSIM".

[Danack]

Undefined constant Imagick::METRIC_SSIM".

So, unless I've missed something, what makes you think that is a valid constant to use?

Or can you point at which underlying constant in ImageMagick you think that corresponds to?

[mikenosp]

Well, as far as I know ImageMagick actually offers SSIM metric since 6.8.3-10. However, the PHP documentation about metrics doesn't show any reference to that constant.

Similarly, in the PHP doc about Imagick::compareImages an user contributed note comments "The Absolute Error metric is not listed as an available metric constant. However, you can still use it if needed by passing the internal constant definition for AE which is 1". This looks consistent with the MetricType enum defined in compare.h so it seems logic I could use 11 and 12 for StructuralSimilarityErrorMetric and StructuralDissimilarityErrorMetric (and the same for other metrics constants still absent in PHP).

Anyway I did a request to both Gemini and Copilot for a PHP function to calculate SSIM using Imagick. The received responses have differences in the code, but both solutions make use of Imagick::METRIC_SSIM:

Gemini:
...
• Make sure that the version of ImageMagick installed on your system is recent (the SSIM metric was added in versions 6.8.3-10+)
...
$result = $image1->compareImages($image2, Imagick::METRIC_SSIM);
...

Copilot:
...

• Requirements:
• • imagick extension installed.
• • ImageMagick with SSIM metric support (Imagick::METRICSSIM).

...
if (!defined('Imagick::METRIC_SSIM')) {
throw new RuntimeException("Your Imagick/ImageMagick doesn't expose Imagick::METRIC_SSIM (SSIM). Update ImageMagick/Imagick.");
}
...
$raw = $imA->getImageChannelDistortion($imB, $channel, Imagick::METRIC_SSIM);
...

Setting aside some typing errors (such as that "METRICSSIM" in the requirements) it seems clear that Imagick::METRIC_SSIM (and others) should be defined in PHP. I don't know however whether or not all metrics types defined in compare.h do actually work as intended. For example, I have applied the pointed internal constants (11 for StructuralSimilarityErrorMetric and 12 for StructuralDissimilarityErrorMetric) in the very simple Gemini code and both metrics give the same result (!):

test_file2.jpg
MSE = 0.37647059559822
SSIM = 0.95352712385079
DSSIM = 0.95352712385079

I don't know whether or not this has to do with the inverted values issue but, to avoid that, Copilot response uses a double check, first calculating the error value using getImageChannelDistortion and laterly comparing the image against itself:

...
$raw = $imA->getImageChannelDistortion($imB, $channel, Imagick::METRIC_SSIM);
$clone = clone $imA;
$self = $imA->getImageChannelDistortion($clone, $channel, 11);
$rawLooksLikeSimilarity = (abs($self - 1.0) < abs($self - 0.0));
...

With a much better result:

test_file2.jpg
RAW : 0.95859081404384 95.86%
SSIM : 0.95859081404384 95.86%
DSSIM : 0.041409185956156 4.14%

[Danack]

I'm slightly annoyed.

Both because this bug report is the result of an AI hallucination, but also because you didn't follow my relatively simple instruction of:

can you point at which underlying constant in ImageMagick you think that corresponds to?

Which meant more work for me reading through a long answer.

Read your original issue report again.

I had absolutely no way to know that "METRIC_SSIM" was meant to mean StructuralSimilarityErrorMetric.

Picking that detail out from your answer, I can point to where the Imagick Magick constants are defined in Imagick code:

#if MagickLibVersion >= 0x707
IMAGICK_REGISTER_CONST_LONG("METRIC_STRUCTURAL_SIMILARITY_ERROR", StructuralSimilarityErrorMetric);
IMAGICK_REGISTER_CONST_LONG("METRIC_STRUCTURAL_DISSIMILARITY_ERROR", StructuralDissimilarityErrorMetric);
#endif

Do me a favour give me some money. Maybe like 50 bucks, or whatever you make in an hour.

both solutions make use of Imagick::METRIC_SSIM:

[mikenosp]

I'm sorry if I annoyed you with my story.

I had absolutely no way to know that "METRIC_SSIM" was meant to mean StructuralSimilarityErrorMetric.

Well, considering that a simple ssim dssim search returns a Wikipedia entry and others about Structural similarity I was sure that 'ssim' term was clear enough about what I was speaking about. Moreover in the second paragraph I wrote:

...the MetricType enum defined in compare.h so it seems logic I could use 11 and 12 for StructuralSimilarityErrorMetric and StructuralDissimilarityErrorMetric

Anyway I apologize for this as well, but while it is true that "METRIC_SSIM" may not be the right wording for that metric, it is also true that there is no common pattern between the metric types as defined in compare.h and their PHP counterparts:

UndefinedErrorMetric -> imagick::METRIC_UNDEFINED
MeanAbsoluteErrorMetric -> imagick::METRIC_MEANABSOLUTEERROR
MeanSquaredErrorMetric -> imagick::METRIC_MEANSQUAREERROR
PeakAbsoluteErrorMetric -> imagick::METRIC_PEAKABSOLUTEERROR
PeakSignalToNoiseRatioErrorMetric -> imagick::METRIC_PEAKSIGNALTONOISERATIO
RootMeanSquaredErrorMetric -> imagick::METRIC_ROOTMEANSQUAREDERROR

I any case, it seems you missed the real problem I was pointing out: whatever their names are, some Imagick metrics (AbsoluteErrorMetric, StructuralSimilarityErrorMetric, and so on) are not exposed to PHP as I said and also another user already explained 11 years ago. Thus, knowing the Imagick SSIM constant is internally registered as METRIC_STRUCTURAL_SIMILARITY_ERROR does not solve the real issue at all because It is equally unusable from PHP code:

Fatal error: Uncaught Error: Undefined constant Imagick::METRIC_STRUCTURAL_SIMILARITY_ERROR in ...

Nice jpeg, by the way.

[Danack]

Well, considering that a simple ssim dssim search

To set your expectations; I do not do random google searches to try to figure out what people are thinking.

I ask them questions such as "Or can you point at which underlying constant in ImageMagick you think that corresponds to?"

are not exposed to PHP

That is just the documentation. which users are free to update.

As to your missing define, please can you run this code, and paste the output back here

<?php

// Start output buffering
ob_start();

var_dump(Imagick::getVersion());

$config_options = Imagick::getConfigureOptions();

echo $config_options["LIB_VERSION"] ?? "LIB_VERSION not set";
echo "\n";

echo $config_options["LIB_VERSION_NUMBER"] ?? "LIB_VERSION_NUMBER not set";
echo "\n";

$rc = new ReflectionClass("Imagick");
$constants = $rc->getConstants();

foreach ($constants as $name => $value) {
    if (str_starts_with($name, "METRIC_")) {
        echo $name . ": " . $value . "\n";
    }
}

// Capture and hash the output
$output = ob_get_clean();
$hash = hash('sha256', $output);

// Emit output followed by its hash
echo $output;
echo "\n---\n";
echo "SHA256: " . $hash . "\n";

Well, as far as I know ImageMagick actually offers SSIM metric since 6.8.3-10

If you think that, please can you point to the earliest version of ImageMagick in https://github.com/ImageMagick/ImageMagick6 that you think has it, and say exactly why you think it was added in that version.