Expert mode
Offers more options to compress your image.
Size (px)
Defines the dimensions of the resulting image.
Trim
Removes any borders or edges of an image which did does not change in color or transparency.
Trim fuzz (%)
Defines a threshold for colors that are not-exactly the same, but should be treated as being the same.
Rotation
Rotates the image clockwise in 90 degree increments.
Brightness
Adjusts the brightness of the resulting image.
Contrast
Adjusts the contrast of the resulting image.
Blurring radius (px)
The Selective Blur is used to blur a background so it can be better compressed.
Contrary to other blur algorithms, the Selective Blur doesn't act on all pixels: blur is applied only if the difference between its value and the value of the surrounding pixels is less than a defined threshold value. So, contrasts are preserved because difference is high on contrast limits.
Blurring threshold (%)
Bit depth
More in my article Finally understanding PNG (#Color depths).
Colors
Specifies the amount of colors used to display the image.
More in my article Finally understanding PNG (#Use 8-bit color depth).
Dithering
Dithering is the process by which we create illusions of the color that are not present actually. It is done by the random arrangement of pixels.
Extreme compression
Use more processor power to get a smaller image without affecting the image quality. Be careful: This is time-intensive and is only used with 8 Bit PNGs.
Quality (%)
Posterizes the image. Posterization entails conversion of a continuous gradation of tone to several regions of fewer tones, with abrupt changes from one tone to another.
Here you can see how efficient the compression of this PNG file is. Dark blue means this area could be well compressed and red means poorly compressed. You can use it for different things:
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Learn more about PNG compression in my article Finally understanding PNG.
The problem that some users can't compress files is a bit more serious than thought. I would ask these users to follow the instructions on the following page: processing.compress-or-die.com/cookie-repair Sorry for the inconvenience. 😔
