Gimp make jpg to Webp 100% quality half size while IM6 make double size. why?

[estatistics]

Same JPG picture with 100% quality in GIMP, and saving all information, without any other processing
a) Saving it as WEBP, result half size.
b) Running  mogrify -quality 100 -format  webp on same JPG picture, double size resulted.

Why? What is doing GIMP and what is doing IM6 mogrify when transforming JPG to webp format?
Note that the differences in picture quality between JPG and gimp 100% webp and im6 100% webp in full zoom are almost not visible.


The original picture.
greek carnaval pic

Because i have GIMP 3, is lacking scipt-fu in menu (why?)
using bash, i try to make all jpg to be saved as webp. How?


gimp -i --verbose -b '(let* (file-webp-save 1 image drawable "$webp_name" "$webp_name" 0 $lossless $quality 100.0 1 1 1 0 0 0 0 67 0))' --batch-interpreter="plug-in-script-fu-eval"

[rich2005]

(5 hours ago)estatistics Wrote: Same JPG picture with 100% quality in GIMP, and saving all information, without any other processing
a) Saving it as WEBP, result half size.
b) Running  mogrify -quality 100 -format  webp on same JPG picture, double size resulted.

Why? What is doing GIMP and what is doing IM6 mogrify when transforming JPG to webp format?
Note that the differences in picture quality between JPG and gimp 100% webp and im6 100% webp in full zoom are almost not visible.

I am not sure what you are trying to demonstrate. The English term is, Comparing Apples with Pears.

As downloaded your image is 1.6 MB (the comment says CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), quality = 90)
Uncompresssed image (as a tiff) 36 MB

Exporting from Gimp
100 quality jpeg 3.7 MB
100 quality webp 1.6 MB
lossless webp 5.3 MB

...different compression formats (jpeg/webp) will give different results, that is expected.

When it comes to exporting webp at various compression settings (no metadata) Gimp and Imagemagick are roughly the same file size.

Quote:Because i have GIMP 3, is lacking scipt-fu in menu (why?)
using bash, i try to make all jpg to be saved as webp. How?


gimp -i --verbose -b  '(let* (file-webp-save 1 image drawable "$webp_name" "$webp_name" 0 $lossless $quality 100.0 1 1 1 0 0 0 0 67 0))' --batch-interpreter="plug-in-script-fu-eval"

What OS are you using For Gimp 3.0 ? Is it possible to run that command line ?
Gimp 3 script-fu is not exactly the same syntax as Gimp 2.10

If you revert to Gimp 2.10 then the BIMP plugin will convert to .webp

[estatistics]

No, try to export from GIMP this image as WEBP and then try to mogrify it as webp with im6. See the difference in file size using in both same (100%) quality?

i found the script-fu menu.

[rich2005]

(4 hours ago)estatistics Wrote: No, try to export from GIMP this image as WEBP and then try to mogrify it as webp with im6. See the difference in file size using in both same (100%) quality?

i found the script-fu menu.

You mean for 100 quality .webp from Gimp = 1.66 MB versus from IM = 5.38 MB (much larger than Gimp)

Probably a bug with IM. Using the convertor binary from Google cweb a 100 quality .webp is 1.7 MB edit: binaries here: https://developers.google.com/speed/webp/download

For values other than 100 Gimp and IM are close in file size.

Quote:GIMP                  IM
644K 90.webp   644K
260K 70.webp   252K
204K 50.webp   200K

[estatistics]

thanks! I must close or tag it solve somehow the thread?

[rich2005]

no problem
Looking at the large IM 100 quality .webp file size, maybe IM uses lossless format instead of "lossy"

edit: it is using webpinfo on the IM webp shows it lossless.

Quote:rich@rich-neon:~/Downloads/libwebp-1.5.0-linux-x86-64/bin$ ./webpinfo 3HD5wzP.webp
File: 3HD5wzP.webp
RIFF HEADER:
File size: 5387762
Chunk VP8L at offset 12, length 5387750
Width: 2848
Height: 4288
Alpha: 0
Animation: 0
Format: Lossless (2)
No error detected.

[estatistics]

gimp also has an option for webp lossless and yet is much smaller than im6 webp convertion.

[rich2005]

(2 hours ago)estatistics Wrote: gimp also has an option for webp lossless and yet is much smaller than im6 webp convertion.

Not on this installation kubuntu 22.04

Gimp lossless = 5377834 B <> IM 100 quality = 5387762 B

[estatistics]

Yes you are right! Gimp lossless creates bigger files than the size of the original JPG. However, the IM6 lossless still produce somewhat larger sizes in 100%.

stat *
File: DSC_1528_gimp100_nolossless.webp
Size: 1,986,982

File: DSC_1528_gimp100_lossless.webp
Size: 5,986,002

File: DSC_1528_IM100.webp
Size: 6,064,204

original jpg
3,665,275

i didnt checked about exif iptc tables and other info. maybe the slight difference is somewhere there.