How big is an 800x600 image file in PNG?

Question

How big is an 800x600 image file supposed to be in PNG? Actually what I would really like is a table that shows resolutions on the y-axis and formats/compression type on the x-axis. I ask this because I thought I saved an 800x600 72dpi image in PNG and it was 1289 kb which seems kind of big to me.

Is there a table showing file size like I describe above? I could not find one with search engines.

Solution 1

Anywhere from somewhere around 150 Bytes to somewhere around 1875 Kilobytes. Compression efficiency depends entirely on the contents. An image consisting only of a single solid color being the best case and maximum entropy color (+alpha) noise the worst.

Reasoning behind these values

The minimum size is just an estimation (created an image and saved it, now updated with PNGGauntlet). Result was a 152 Byte file.

The theoretical maximum payload size is 800 * 600 Pixel * 4 Bytes per Pixel (1 Byte per R/G/B + Alpha) = 1,920,000 Bytes. Adding to that are headers and compression overhead.

Solution 2

The size of a PNG depends on what the image contains. There is no way to predict the filesize based solely on the dimensions of the image.

If you want the smallest PNG possible, run your image through PNGGauntlet. It will try several PNG compression tools and then output the one with the smallest filesize.

Solution 3

I believe that PNG files are lossless compressed files of the image. So it is very difficult to predict the size of the file since we don't know how the colors are arranged on the image. In fact, the PNG file could even be larger that the raw image data itself.

Comments

[barlop]

That is a complicated question because there are different forms of PNG and I would imagine that an image that is just bright yellow is smaller compressed, than a detailed image.

[barlop]

Not only is there 8bit and 24bit png, you can select the compression used with it libpng.org/pub/png/pngfaq.html "PNG provides a lot of flexibility in tuning the compression level of an image, from trimming the color and transparency palettes to choosing the precise combination of pre-compression filters to choosing the proper settings for the compression engine itself. (GIF, on the other hand, is practically deterministic;"

[barlop]

btw re your big file I suppose you mean KB not kb. B=byte b=bit. Graphic designers often learn about what file format to use. Also if you open a file you (in some programs) can see its uncompressed size. photoshop shows it though photoshop is not freeware.

[barlop]

How did you calculate the 1000byte (you now say 150bytes) -1400KB range?

[barlop]

-1 ypu say in your edit that you estimated a min size and got it wrong. I suppose you estimated and i'd bet you got your max size wrong too. What calculation did you do for your "estimate". I notice your estimate happens to be floppy disk size. I hope you didn't just pick it 'cos a floppy disk sprung to mind.

[Daniel B]

@barlop Relax dude, I’m not a computer. In my previous maximum size calculation I forgot about the alpha channel. If created by hand, you could probably make an even smaller image, but that’s just for sport.

[barlop]

now you have provided your calculation, i'll remove my -1. I can't comment on the calculation, but at least you provided one. Worth bearing in mind though there is 8 bit png and 24 bit png, I suppose that'd make a difference to the calculation?

[Daniel B]

@barlop The program (Paint.NET) already creates an 8-Bit PNG whenever feasible, like in this case. As to what PNGGauntlet does, I’m not so sure. :)