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PNG Preprocessor PlugIn


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PNG Preprocessor prepares images for being saved as PNG. It optimizes the size of the file to 40-80% of the original size. This is done by combining nearly same colors to one, so the PNG compression algorythm can work more effective. You normally won't be able to see the difference between the compressed and the original image.

Download: PNG_Preprocessor.dll (8,19 KB)


Before: 1860 KB
After: 957 KB
Click the images to see full size - Photo taken by me

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PlugIns Made in Germany

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Interesting. The only place I can see any difference at all in your sample is the sky.

I'll have to try this out once I get over my newfound Questionable Content and Starcraft 2 addictions.


ambigram signature by Kemaru

[i write plugins and stuff]

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Just to clarify... will this optimize the size even more than what optipng already does? (I would guess yes, since optipng is lossless and this sounds like it has at least some loss...)

Thats why its different to OptiPNG: It is an effect ( not a file format ) which just prepares the image for being saved, after that you can save it with PDNs standart PNG format. So the 100% compatibility to PNG is guaranteed.

Yes, it has some loss, but if you use the same settings in the same imaage twice there won't be more lost then after the first use.

It is also not limited to PNG, you can use it with every other format that has similar compression techniques (e.g JPG). I made it mainly for PNG cause i made an app which does the same only for PNG before i put it into a PlugIn.<br><br><br>EDIT: I saw OptiPNG gets results between 50 and 80%, PNG Preprocessor gets also these results with most images, but i also tested some and got only 20 to 60% of the original size. You have to decide with how much quality loss you can agree.<br>

Edited by niwax

PlugIns Made in Germany

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but 80% does sound impressive

It depends on your image - photos will get to 50-80% of their original size and screenshots 20-80%. The example was compressed with strength 3 of 5.

PlugIns Made in Germany

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  • 2 years later...
  • 3 years later...

One of my favorite plugins. Great work. Also, photos need to be reuploaded.


Here are some photo comparisons, since the ones provided by OP are broken. In all compressed images, maximum level of compression (5/5) was used.


Audi A5 before (321 KB in PNG):



Audi A5 after PNG Preprocessor (185 KB = 57.6% of original size)


Audi A5 High-Quality JPEG : 41.59 KB

Lena Söderberg before (1.77 MB)

Lena Söderberg after (978.2 KB = 55.3%)

Lena Söderberg High-Quality JPEG : 134 KB

"Pub" by GUWEIZ on DeviantArt (1.45 MB)


"Pub" by GUWEIZ after (790 KB = 54.5%)

"Pub" High-Quality JPEG : 242.15 KB

A page in the manga Nisekoi before (264 KB)

The same page after (176 KB = 66.7 %)

Manga page High-Quality JPEG : 183.49 KB

A transparency gradient before (179 KB) :


Transparency gradient after (56.6 KB = 31.6%) :


Transparency gradient High-Quality JPEG : Not Applicable (JPEG doesn't encode transparency)

In conclusion, I have found that color images such as photos or complex pieces of artwork can be compressed to about 55% of the original size on average, whereas simpler grayscale images can be compressed to 65% of the original file size. The only noticeable deteriorations I have found are transparency gradients and dark gradients.

This compression method gets results that can be comparable to high-quality JPEG for much less noticeable deteriorations.

Edited by Rei
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