Image size is different in GIMP than desktop

[vakita]

Using Windows 10 and Gimp 2.8  When I look at the properties of a .png image on my desktop is says it is 377KB  but when I open it in GIMP underneath the canvas it says image.png (2.7 MB)
It's not a problem, I'm just wondering, why the difference ?

[rich2005]

(04-07-2017, 06:18 PM)vakita Wrote: Using Windows 10 and Gimp 2.8  When I look at the properties of a .png image on my desktop is says it is 377KB  but when I open it in GIMP underneath the canvas it says image.png (2.7 MB)
It's not a problem, I'm just wondering, why the difference ?

The small value is the file size and can vary depending on which format and compression the image is saved. 

   
png in Gimp is saved with a high level of compression but is lossless. What you export is what you get back
Export as a jpeg and that is a 'lossy' format and depending on the amount of compression amounts of image information is lost.

The value you see at the bottom of Gimp is the size of the image being processed is not compressed and will includes any extra layers etc that might be lost when exporting to a png or jpeg.

That is why the default 'save' in Gimp is Gimps .xcf format which is lossless and keeps all layers, masks, transparency which will be lost with other formats

[vakita]

I'm still a little confused but, if I understand correctly, if I want to continue to make changes to an image at a later time, I should save them as an xcf file. Also a jpg will loose some quality each time it is exported, so in order to avoid that I should use png. If I am finished making changes to an image that I want use on a website would you recommend that I export it as a jpg as opposed to png for the advantage of the much smaller size ?
I appreciate your taking the time to help. Thank you.

[Ofnuts]

(04-07-2017, 08:12 PM)vakita Wrote: I'm still a little confused but, if I understand correctly, if I want to continue to make changes to an image at a later time, I should save them as an xcf file.

Yes.

(04-07-2017, 08:12 PM)vakita Wrote: Also a jpg will loose some quality each time it is exported, so in order to avoid that I should use png.

No. If you have a "perfect" image (XCF, PNG, TIFF) and export it to JPG multiple times, you get a loss but it's the same loss every time from the initial perfect image. The problem of cumulative loss arises when you export to JPG, then reload the JPG to edit it and re-export to JPG (typically what many people do with JPG from their camera). And even then, the loss is not as important as what most people think.  If the file is saved back with the same settings (and by the same code) the same encoding is produced for 8x8 blocks with unchanged pixels. So after an initial loss due to the first  compression, further loss will happen only around changed pixels. In other words, as long as you do "local" editing you don't lose much. But changing quality settings or doing some global change (constrast, luminosity, etc...) will entail a new loss (although likely less than the initial one).

(04-07-2017, 08:12 PM)vakita Wrote: If I am finished making changes to an image that I want use on a website would you recommend that I export it as a jpg as opposed to png for the advantage of the much smaller size ?

It depends a lot on the image... For photo JPEG is usually somewhat smaller. For computer graphics (logos, text) PNG is smaller, and in any case the sharp edges and high contrast of these pictures make the compression artifacts of JPG very visible, so JPG is best avoided... But under 100K size is nothing to worry about, most web pages are over severam megabytes these days, due to all the javascript.

[vakita]

All right, I will try and digest all of of this, over the next few days. Thanks again for your help.

[sallyanne]

If you check in gimp (image properties) the file size is often different to what it says down the bottom size in memory.