(02-20-2022, 07:11 PM)Corsari Wrote: Around the web you read pages where they say same jpg image same quality in webp will be significantly smaller
Well I tried with Gimp exporting to webp and the result is not smaller
Depends upon the process. The more you give .webp to work with, then the better your results ...If you are taking an image that is already compressed as a .jpg and converting that to .webp and expecting a considerable reduction in file size, you likely are not going to be very impressed.
But taking a full resolution .png image and converting it to .webp, you are going to be impressed with how much smaller the end file size compared to the same image converted to .jpg ...and the .webp is going to look better.
Just as a comparison I just took a 286 KB .png image, and converted it to a 62 Kb .jpg, compared to the same image converted to a 36 KB .webp
Mostly I use .webp for animations. An .mpg video clip that converts to 35 MB as a gif, instead reduces to only about 13 MB as a .webp...and additionally there is not that insane limitation to only 256 colors that you get with .gif.
So, I use .webp for qualitative reasons, and not just for file size.
It is how they measure the image quality also the compression value is not equivalent between formats.
Quality ? Look up ssim. Using ImageMagick gives a ssim value
A comparison using a scanned in photo 300 ppi exported as a png for the reference image.
A 90% jpeg size 0.67 MB has a quality difference (ssim) 0.96 versus a 95% webp size 0.61 MB ssim 0.96
That end of the scale roughly equivalent here, a small saving on file size.
The other end of the scale 60% jpeg size 0.31 MB ssim 0.93 versus a 75% webp size 0.23 MB ssim 0.92
Roughly the same quality with a smaller file size, about a 25% saving.
It is a format for web use I'm not going to archive any photos with it.
02-21-2022, 09:35 AM (This post was last modified: 02-21-2022, 09:37 AM by rich2005.)
Quote:So if you have an optimized and compressed JPG that appears "good", no reason to use webp
Not necessarily, There will be situations where you need to squeeze a bit out of the file size for posting on a web site. Jpeg compression is not linear, values 60 and below, plenty loss in quality for not much reduction in file size.
PNG format: png image = 195 KB Lossless (for equivalence) webp = 175 KB a 10 % saving but with 90 compression the webp = 71 KB
As the old saying goes, You pays your money, You makes your choice Up to you to decide on format depending on circumstance.
Video is more dramatic.
48 frames pulled out of a video - a cartoon, small frame 320x218 suitable for animations, as 48 individual jpegs of not great quality.
exported as an optimized gif animation, size 843 KB
exported as a 50 quality webp animation size, 160 KB an 80% saving in size and you keep all the colours.
Smaller yes, drastically smaller, not necessarily if you want to keep equivalent image quality. Tried with this image:
Exported as Jpeg: 185K, as WebP: 137K. (used Q=90 for both, whatever that means). So this is about a quarter smaller in WebP format.
Then you have to understand that all these lossy compression schemes are data dependent, they work better on uniform and clean areas than on noisy ones. In the Webp export dialog, you can indicate the type of document and this may influence some compression parameters. In the Jpeg export dialog, the "chroma subsampling" in the advanced options is the main factor for the output size. Color information can be stored as a half-size image (one fourth the pixels) and this alone divides the total size by two (there is also a chroma subsampling in WebP, but this isn't an option you can tweak).
