WordPress at a glance
filter is not described

wp_editor_set_quality filter-hook . WP 3.5.0

Filters the default image compression quality setting.

Applies only during initial editor instantiation, or when set_quality() is run manually without the $quality argument.

set_quality() has priority over the filter.

Usage

add_filter( 'wp_editor_set_quality', 'filter_function_name_1902', 10, 2 );
function filter_function_name_1902( $quality, $mime_type ){
	// filter...

	return $quality;
}
$quality(int)
Quality level between 1 (low) and 100 (high).
$mime_type(string)
Image mime type.

Where the hook is called

WP_Image_Editor::set_quality()
wp_editor_set_quality
wp-includes/class-wp-image-editor.php 238
$quality = apply_filters( 'wp_editor_set_quality', $this->default_quality, $this->mime_type );

Where the hook is used (in WP core)

Does not used.