Free online JPEG optimization tool with a very high compression ratio.
Accepts JPEG, PNG, WEBP, HEIC and BMP images.
Usage summary: Do not increase "Quality" above 85,
and leave "Chroma subsampling" at "2x2".
About JPEG format
JPEG was created in 1992. It is a "lossy" format (in practice, there is no
such thing as "lossless jpeg"), therefore output JPEG will always have worse visual quality
than input image (even at Q=100). Common mistake is to increase "Quality" until no visual
difference in output JPEG is noticed. JPEGs are supposed to lose some visual quality.
JPEGs can never have transparency, they do not have opacity or alpha channels.
This is one of the most known JPEG issues. JPEGs have 2 different internal modes:
- Usual YCbCr mode, which allows saving full color 24-bit images.
- Grayscale 8-bit mode for grayscale images. Note, that it is always possible
to save grayscale images using 24-bit YCbCr mode, but 8-bit grayscale mode is more compact.
Also note, that grayscale mode never performs chroma subsampling.
Privacy
Compression is 100% performed in a browser (JavaScript).
Not a single image byte is ever uploaded to a server. Not even file name, type, or very fact that image
was opened is sent to a server. Server does not collect absolutely anything about images.
But website uses "Google Analytics", which collects general information
about visiting users: how many users visited, from what countries, what browsers they used, etc.
All cookies added by the website come solely from "Google Analytics".
Metadata
Absolutely all (100%) metadata is discarded from output JPEGs: date, camera model,
location, thumbnail, exif, orientation, color profile, etc.
Performance
Compression speed completely depends on your computer CPU, RAM and browser.
Usually Chrome is slightly faster than other browsers.
Generally, speed is slow, because compression takes place in browser
(JavaScript) level, and many JPEG compression enhancements are used.
Limits
There are almost no limits to input images:
- Input image file size is symbolically limited to 100 MB
(just to prevent accidentally opening non-image files).
- Maximum width & height is limited to 65500 px (because that is JPEG standard limit).
- Everything is 100% free (mostly because compression uses your own computer).
"Quality" setting
Quality (Q) values 1-100 are not percentages. Specifically,
Q=100 does not mean that image will not lose quality.
Q=50 produces images with best quality/size ratio. Moving quality towards 100,
image size increases faster than quality. Moving towards 0, quality decreases faster than size.
Probably back in 1992, when JPEG was created, Q=50 was intended to be a default value.
Quality values are not the same among different programs.
One program might produce better quality images at Q=70 than other at Q=80.
"Chroma subsampling" setting
After reducing overall image quality with "Quality" setting,
quality of image colors can be additionally reduced with "chroma subsampling" setting.
Because this setting affects only colors, grayscale images do not have it.
- Value "1x1" disables this step. Colors quality is not additionally reduced.
Should use it when Q > 95. Can consider using it when Q > 85.
- Value "2x2" is by far the most useful, because it significantly
decreases image size without noticeable visual quality loss. Use it for all customary images.
- Value "3x3" does not reduce size so much.
Can consider using it when "Quality" is low and size is important.
- Value "4x4" does not reduce size almost at all. Should probably never be used.
"Transparency" setting
Because JPEGs cannot have transparency, if input image has transparency, "Transparency"
setting will appear, and transparent pixels will be converted to either "White" or "Black" color.