Re: [Gimp-user] Layer groups seriously broken - huge resource hog

[Ofnuts <ofnuts gmx com>]

On 06/16/18 12:38, BWK wrote:
> I love Gimp. I started using it about a year ago and it is the second most used
> piece of software on my computers. I often use it on two of my computers at the
> same time. I do stuff with it mostly with aerial photo mosaics up to 500
> megapixels - aerial photo tiles joined together with other aerial photos
> overlaid over the top of them. With the new unified transform tool in Gimp 2.10
> an aerial photo overlay can be completed in one step of transformation thus
> maximising the quality and speeding up the work. The software is brilliant for
> this.
>
> Nevertheless there seems to be significant shortcomings in the implementation of
> layer groups in Gimp. I started using them because I had a lot of layers in my
> projects and I wanted to keep everything tidy. But as my projects have grown, I
> have found that layer groups are a huge waste of resources. With the biggest
> project, the file size of the project doubled from 4 GB to 8 GB when layer
> groups were used, with exactly the same layers. Part of creating these aerial
> photos is to split them into tiles to be loaded into a GIS for mapping. This
> requires resizing the canvas to crop the boundaries to a tile boundary and then
> exporting the tile out as a JPG. Most of these tiles are only 4800x7200 pixels
> that should not really be a problem for the computer. But with layer groups it
> takes about 15 minutes to do the canvas resize with the disk constantly
> churning. Without layer groups it only takes about 15 seconds. The export itself
> is much faster with far less disk churning as well.
>
> I only discovered this by accident when in one of my projects Gimp constantly
> crashed when saving the project as soon as I added more than three layers to a
> layer group. Obviously Gimp is broken in that area (and doesn't throw any kind
> of error message or exception either, it just quits) but the result of having to
> take out the layer groups I was putting in and working without them has had the
> unexpected benefit of a huge time saving after allowing for a lost day trying to
> work out what the crashing was about.
>
> If this feature is going to be any good in Gimp in the future the implementation
> of it needs serious attention.

Layers groups are not meant to keep things tidy. They are meant to force 
the compositing order, like parentheses in a mathematical equation. 
Groups have their own opacity, blending mode (and layer mask in 2.10).  
Layers in a group are composed, resulting in a virtual layer, which is  
composed with the layers (or virtual layers from groups) in the parent 
level...

It is possible that layers groups add just enough memory to overflow the 
tile cache and force Gimp to work with a swap (this really slows tings 
down).  See Edit>Preferences>System resources>Tile cache size and set it 
to as much as possible (your available RAM minus what you need for your 
system and other apps).

Something that can help keep things tidy in 2.10 is t use color tags on 
the layers.