Re: [Gimp-developer] Size on disk vs size reported on status bar

[Elle Stone <ellestone ninedegreesbelow com>]

On 10/03/2017 09:33 PM, Jehan Pagès wrote:
> I don't know how this info is computed in GIMP code (i.e. does it
> check for actual memory size or does it do some basic maths as I am
> about to do), but assuming your image is 8 bits per channel, and all 7
> layers are the size of the image and have no alpha, that makes:
> 4000*6000*7*24 = 4 032 000 000 / 1024^3  ~ 3.8GB!:-)

Hi,

Actually the image is at 32-bit floating point precision, all the layers 
have alpha channels, most of the layers have masks, and there are a 
couple extra channels (saved masks) in the channels dialog.

Ignoring the masks and the extra saved channels, and assuming I'm doing 
the right math, this would be:

4000*6000*7*32*4 = 21 504 000 000 / 1024^3 ~ 20 GB

As an experiment, I followed Simon's suggestion and made a new document, 
same size, 7 layers, and filled each layer with random LCH noise. This 
brought the %m value up to 4.8 GB.

Removing all operations from the Undo history brought the %m value down 
to 2.9 GB. Saved to disk, the size is 1.6 GB. I guess random noise also 
compresses?

Best,
Elle