File Size Increase with little/no changes

[Elagens]

Hello, and thanks in advance for advice.

 

I was attempting to make alterations to a .PDF that was not editable in Acrobat.

 

I exported the .PDF to .PNG format (230 KB, 13200x8400 at 300 pixels/inch).

 

After deleting and rewriting two words, I saved a new .png file and found that the minor change increased the file size to 1100 KB.

 

Finding that unusual, I opened the original .PNG and used 'save as' to create a new file with no changes, and it also ballooned to 1100 KB.

 

Is there an explanation for why a file would substantially increase in size upon saving it in Paint.net when no alterations have been made to canvas size or resolution?

 

Is there a way to maintain a file size similar to the original image without reducing canvas size by a quarter?

 

Thanks again,

[Rick Brewster]

You're comparing a 230 KB PDF to a 1100 KB PNG? They are completely different ways of encoding. They are not comparable.

[Elagens]

No, I'm not comparing a 230 K PDF to anything. The size of what was once a PDF is irrelevant, I was merely giving some background to the issue.

 

I exported the .PDF to .PNG format (230 KB, 13200x8400 at 300 pixels/inch).

 

 

Once the 230 K PNG was opened in Paint.net, any attempts to alter it, or even save it with no changes, caused it to become a 1100 K PNG.

 

Is there an explanation for why this happens and a way to maintain a similar file size without reducing the image quality?

[Rick Brewster]

Squashing PNGs is a CPU intensive process (i.o.w it takes a LONG time). If you need your PNGs to be as small as possible, use something like pngcrush or PNG Gauntlet. It's like when you make a ZIP file and can choose various compression levels. Low compression produces bigger file sizes but takes the least amount of time. High compression produces smaller file sizes but takes the longest amount of time. An application like Paint.NET, where saving is frequent, must err on the side of speed (it's actually just using the system's GDI+ codec for this which doesn't even allow that to be configured).

 

There may also be differences in the bit-depth of the input and output PNGs. Paint.NET always stores things internally at 32-bit BGRA. So if your PNG started as 8-bit, and you made some changes which require it to be saved at a higher bit-depth (I'm assuming you left the bit-depth setting to "Auto" in Paint.NET), it could certainly cause the file size to go up.

[midora]

You should check the settings in the png save settings dialog.

It's not normal that the size of a png increases by a factor of 3 just by resaving.

The important thing is the number of colors you are using.

An 8-bit png (max 256 colors) needs much less space than a 24bit one.