Extremely large xcf file with 8 layers

[jrickards]

Hi:

GIMP 2.10.34 on Linux Mint

I opened 8 ~16Mpx photo images as layers. I first tried 8 PNG (~80MB each) but the XCF file was huge (919MB) so I exported the photos from darktable as JXL (~4MB each) and the XCF was still huge (925MB), both XCF saved with the higher compression option.

Photoshop has a "Place Linked" option which I presume doesn't copy the placed files into the working file, presumably creating a much smaller saved copy of the working file. (I have PS at work but I haven't explored this option so I'm guessing).

Is there any way to create a layered XCF file that isn't so huge?

[PixLab]

(10-24-2024, 01:14 AM)jrickards Wrote: Hi:

GIMP 2.10.34 on Linux Mint

I opened 8 ~16Mpx photo images as layers. I first tried 8 PNG (~80MB each) but the XCF file was huge (919MB) so I exported the photos from darktable as JXL (~4MB each) and the XCF was still huge (925MB), both XCF saved with the higher compression option.

Photoshop has a "Place Linked" option which I presume doesn't copy the placed files into the working file, presumably creating a much smaller saved copy of the working file. (I have PS at work but I haven't explored this option so I'm guessing).

Is there any way to create a layered XCF file that isn't so huge?

We need to know a lot more than "xcf are huge"

What are the resolution of those images? are you working in 32-bit floating point? what do you do when working with GIMP, how many layers? Are the images meant for internet/website or to be printed?

[rich2005]

(10-24-2024, 01:14 AM)jrickards Wrote: ...
I opened 8 ~16Mpx photo images as layers. I first tried 8 PNG (~80MB each) but the XCF file was huge (919MB) so I exported the photos from darktable as JXL (~4MB each) and the XCF was still huge (925MB), both XCF saved with the higher compression option.
.......Is there any way to create a layered XCF file that isn't so huge?

It does not really matter much about the original image format, jpeg will be 8 bit lossy-compressed / png 8 bit (probably) lossless-compressed / tiff (alsorts) when inside Gimp the format is just pixel information so the size generally shows larger than the sum of original images. Coming from Darktable then the precision is probably 32 bit floating point and correspondingly larger than an 8 bit image.

Then you can add on any alpha channels and while Gimp is open any undo information.

When it comes to saving a Gimp .xcf image, it is compressed to certain extent (run-length encoding I think) and is lossless.
For a slightly smaller file size you can use secondary compression and save as a .xcf.gz and a comparison.
8 layers (jpegs about 7.5 MB each) 545 MB in Gimp saves ,xcf 8bit as 381 MB .xcf.gz 304 MB and "better" .xcf.gz 280 MB a bit of a saving
32 bit float is 2.6 GB in Gimp and similar, a 32 bit "better" xcf.gz file size is 436 MB
...obviously depends on images, do your own comparisons.

Quote:Photoshop has a "Place Linked" option which I presume doesn't copy the placed files into the working file, presumably creating a much smaller saved copy of the working file. (I have PS at work but I haven't explored this option so I'm guessing)

I am guessing this is similar to Inkscape importing a bitmap image. Your choice, embed into the image or add a link to the file.
It depends how trusting you are. Move to a different computer / network and the source(s) might disappear. Using Cloud storage ? Here today , Gone tomorrow.

[Ofnuts]

(10-24-2024, 01:14 AM)jrickards Wrote: Hi:

GIMP 2.10.34 on Linux Mint

I opened 8 ~16Mpx photo images as layers. I first tried 8 PNG (~80MB each) but the XCF file was huge (919MB) so I exported the photos from darktable as JXL (~4MB each) and the XCF was still huge (925MB), both XCF saved with the higher compression option.

Photoshop has a "Place Linked" option which I presume doesn't copy the placed files into the working file, presumably creating a much smaller saved copy of the working file. (I have PS at work but I haven't explored this option so I'm guessing).

Is there any way to create a layered XCF file that isn't so huge?

The format of the input file is irrelevant, what count is the size in pixels, because compressed format like JXL are expanded.

What makes a great difference if the image precision. The image is either in 8-bit/channel (one byte) ("native" precision of JPEG/PNG) or 32-bit/channel (4 bytes) (high precision). There are also 16-bits/channel precision modes but they are unimportant. Depending on input format, and settings (Preferences ➤ Image import and export ➤ Import policy ➤ Promote imported images...) the image is loaded in 8bpc or 32bpc. Of course if you come from a raw, using 8-bit precision is shedding useful bits of information.

If you load the image, the RAM you use is width × height × 4 (channels) * (layers+2) bytes (the 2 additional layers are actually buffers for the composite image). So with my 20Mpix camera, 8 layers are 764MB in low precision, and 3.2GB is high precision.  And of course when you work on it you add undo snapshots...

When you save the image as XCF, there is a compression option at the bottom of the file dialog. Using my 8 random pictures of vintage cars, I get:

             RAM Size   Plain XCF   Compressed XCF
             --------   ---------   --------------
     8 bpc:    764MB      422MB         210MB
    32 bpc:    3.2GB      1.3GB         305MB

so the compression is quite efficient (but is also quite slow) .

[jrickards]

Thank you for the information. I didn't know about the .gz option, it'll help, if only with archiving old projects.

Linked files would work for me, I put all resources for a project in a folder and keep them together and archive them together.