PNG compression

Questions and comments about Other World Mapper.

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SilverSurfer1221
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Re: PNG compression

Post by SilverSurfer1221 » Thu Apr 08, 2021 10:08 am

In any case, the point is simple - OWM is not at fault here. It looks to be doing what it's supposed to be doing - creating a PNG file that appears to be the correct size based on the dimensions and DPI you have set. It does not look to be compressed (especially since the intent of PNG is to be lossless/uncompressed). The exported file sizes of PNGs from OWM seem to be inline with what other graphics software export for PNG of the same size.

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Balmung
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Re: PNG compression

Post by Balmung » Thu Apr 08, 2021 10:15 am

Unless you have access to the source code - or have an information from the developers, which is the intention of this thread - you don't know it 100%.

It is true that some software don't ask the user for a compression level, but it's also true, that some other do ask the user for it.
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SilverSurfer1221
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Re: PNG compression

Post by SilverSurfer1221 » Thu Apr 08, 2021 10:16 am

I guess you're right - no need to give you relevant information that can help you to answer your original question. I'm not trying to be mean in any way, but just trying to respond to what you've said. Is the PNG from OWM compressed? The answer appears to be no. Why? Because the exported PNG file size from OWM is consistent with exported PNGs of the same size from other professional software, like Photoshop, Affinity Photo and Designer, and Clip Studio Paint. The outlier here seems to be Inkscape, which is an opensource piece of software (by comparison to the others mentioned here).

You may not want the information on PNG, but if you're going to be creating images and you're going to be asking questions and offering input on feature requests and the like, isn't it a good idea to at least have a bit of working knowledge of these things? You may just be a user of these pieces of software, but what's the harm in learning a thing or two about them? There are reasons that various file formats are offered to end-users and it's more than just because they exist. It's because they each serve a purpose of their own and it's good to have at least a base working knowledge of what that is.

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SilverSurfer1221
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Re: PNG compression

Post by SilverSurfer1221 » Thu Apr 08, 2021 10:18 am

You're right. I don't have access to the source code. But, in this case, I don't need to. It's pretty easy to see what's going on.

But I did learn something from your posts - you don't want to hear what anyone else has to say other than the developers. So, fine. I'll not respond to your posts. Have a nice life. OWM is a great piece of software. Enjoy it.

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Balmung
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Re: PNG compression

Post by Balmung » Thu Apr 08, 2021 10:23 am

This is not a feature request, this is just a question for the developers and I'm looking for concrete information.

It's like our discussion with the grid sections: 99% accuracy is like no accuracy at all ;)
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Kanchou
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Re: PNG compression

Post by Kanchou » Thu Apr 08, 2021 11:05 pm

Guys be nice to each other, I really don't like having to do moderating :lol:

Short answer: OWM does not compress formats that aren't typically lossy. So PNG, tiff, etc. are uncompressed. Jpeg is the format the only one that enables the "quality" slider (tied to compression).

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nDervish
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Re: PNG compression

Post by nDervish » Fri Apr 09, 2021 4:56 am

SilverSurfer1221 wrote:
Thu Apr 08, 2021 9:30 am
PNG is not meant to be compressed. As a file format, it is meant to be uncompressed ... it's supposed to be a lossless file format.
Erm... Ever use a .zip (or .gz, or .tgz, or .rar, or .7z, or...) file? Lossless compression is a thing. PNG is both compressed and lossless. If it wasn't compressed, then your blank white page PNG file wouldn't be 400k, it would be the exact same size as every other PNG file with the same number of pixels, because "uncompressed image" means that every single pixel is recorded individually, as in a .RAW file format.

GIMP, etc. offering different levels of compression is also not evidence of lossy compression. ZIP and gzip file compression also offers multiple levels of compression (typically 9 levels, so you can specify them with a command-line parameter of -1 through -9) and they are 100% lossless formats; the different compression levels control how hard it looks for identical sections of data that can be deduplicated, they don't tell it to start throwing away or approximating things.

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Re: PNG compression

Post by nDervish » Fri Apr 09, 2021 5:07 am

Kanchou wrote:
Thu Apr 08, 2021 11:05 pm
Short answer: OWM does not compress formats that aren't typically lossy. So PNG, tiff, etc. are uncompressed. Jpeg is the format the only one that enables the "quality" slider (tied to compression).
I hate to disagree with you about your own software, but this is not correct. I just opened an OWM-exported PNG file in GIMP and re-saved it as a PNG with compression level 9 (the maximum). The GIMP-exported, maximum-compression version is basically the same size (0.2% difference). Then I exported it from GIMP again at compression level 0 (uncompressed) and the uncompressed version is roughly four times as large. So your PNG library seems to be applying (lossless!) compression by default.

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Kanchou
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Re: PNG compression

Post by Kanchou » Fri Apr 09, 2021 10:24 am

nDervish wrote:
Fri Apr 09, 2021 5:07 am
Kanchou wrote:
Thu Apr 08, 2021 11:05 pm
Short answer: OWM does not compress formats that aren't typically lossy. So PNG, tiff, etc. are uncompressed. Jpeg is the format the only one that enables the "quality" slider (tied to compression).
I hate to disagree with you about your own software, but this is not correct. I just opened an OWM-exported PNG file in GIMP and re-saved it as a PNG with compression level 9 (the maximum). The GIMP-exported, maximum-compression version is basically the same size (0.2% difference). Then I exported it from GIMP again at compression level 0 (uncompressed) and the uncompressed version is roughly four times as large. So your PNG library seems to be applying (lossless!) compression by default.
No problem, I appreciate the correction! Was that in Linux or Windows? In Linux/OSX libpng does the encoding of the png export and it must be doing (lossless) compression by default.

In Windows we don't have control over it.

Thank you!

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Alejandro S. Canosa
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nDervish
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Re: PNG compression

Post by nDervish » Sat Apr 10, 2021 7:18 am

Kanchou wrote:
Fri Apr 09, 2021 10:24 am
No problem, I appreciate the correction! Was that in Linux or Windows? In Linux/OSX libpng does the encoding of the png export and it must be doing (lossless) compression by default.
This was in Linux. I didn't think to try on Windows (I use both versions of OWM, but I'm always in Linux when reading forums), but, yeah, it may behave differently depending on the PNG library. I hadn't thought of that detail...

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