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png quality when re-saving


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I though png was a lossless format. Whenever I re-save a png file, lets say after I resized it to be smaller, I end up with a bigger file. And If I size down the original file and the resized to a smaller image, the resized will look distorted.


I don't know if this would happen in PS and what should I do instead, save it as a jpeg?

Edited by nicoliani
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PNG is a lossless format, but file sizes depend on how long you want to spend optimizing it.

Reason for file becoming bigger after resizing it smaller, most likely is due to blurriness? If the initial image is optimal for PNG, sharp lines, no gradients, few colors, it works great. Resizing produces artifacts which are very costly to store lossless.

One option is to try

OptiPNG optimizes the file as much as possible.

Edited by Zagna


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I've always found optimising the size of a .PNG a very hit or miss affair and it is of great importance to me too because I use PDN to create a lot of personalised icons/thumbnails for certain retro games' console use. There is an upper total size memory limit for such graphical files in one case which if exceeded mean icons won't be displayed and the whole console navigation slows down.


Basically the smaller the file size the better, preferably <50KB  but I need maximum image quality and JPGs, in some cases, simply are not good enough.


The way I've been doing it up until I read this is to save the original PDN created image as a PNG then use another graphics program with PNG optimising tools to decrease the colour depth and then save again as PNG. That way I can often get a >50KB PNG well below 50KB without it visibly affecting the picture quality.


Having to use a second graphics tool for this is inconvenient so if that OptiPNG plugin can be used in the same way it will be a real help.


Had a problem getting it to work, I think I must have somehow installed the version shown as not working with PDN v4.0>, but I reinstalled what is definitely the most recent version and now have an Optimized PNG save option. Great.


Not as comprehensive as the other program's options mentioned but even if it only saves me having to use that 50% of the time it is still worth having.



Edited by IHaveNoName


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