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\ No newline at end of file +PROLOGUE + redshift-ng is a fork Redshift. redshift-ng strives to keep backwards + compatibility with Redshift and be usable as a drop-in replacement. + Therefore, redshift-ng implements the command "redshift" just like the + original Redshift implementation. + +NAME + redshift - Automatically adjust display colour temperature according the Sun + +SYNOPSIS + redshift [-b day:night] [-c file] [-g r:g:b] [-m method[:options]] + [-l latitude:longitude | -l provider[:options]] + [-o | -O temperature | -t day:night | -x] [-hpPrvV] + +DESCRIPTION + redshift adjusts the colour temperature of your screen according to your + surroundings. This may help your eyes hurt less or reduce the risk for + delayed sleep phase syndrome if you are working in front of the screen + at night. + + The colour temperature is set according the the position of the Sun. + A different colour temperature is set during the night and during the + day. During dawn and early morning, the colour temperature transitions + smoothly from night- to day-time temperature to allow your eyes to + slowly adapt over a period of about an hour. At night, the colour + temperature should be set to match the maps in your room. This is + typically a low temperature at around 3000K–4000K (default is 4500K). + During the day, the colour temperature should match the light from + outside. Typically around 5500K–6500K (default is 6500K). The light has + a higher temperature on an overcast day. + + In addition to the command-line tool redshift, the GUI redshift-gtk + provides an alternative interface that shows up as a notification icon + in the desktop environment. + +OPTIONS + The following options are supported: + + -b day:night + Screen brightness to apply at daytime and at nighttime. + (Default: 1:1) + + The value most be between 0.1 and 1.0. + + -c file + Load settings from specified configuration file. + + -g r:g:b + Additional gamma correction to apply. (Default: 1:1:1) + + -h + Display help message. + + -l latitude:longitude + Your current location, in degrees. Shall be formatted a single + real number, rather than split into integer degrees, minutes + and seconds. The location should be specified using the GPS + coordinate system. + + -l provider[:options] + Select provider for automatic location updates. + + Use "-l list" to see available providers. + + Use "-l provider:help" to see available options. + + -m method[:options] + Method to use to set colour temperature. + + Use "-m list" to see available methods. + + Use "-m method:help" to see available options. + + -o + One-shot mode (do not continuously adjust colour temperature). + + Use this with the -P option to clear the existing gamma ramps + before applying the new color temperature. + + -O temperature + One-shot manual mode (set colour temperature). + + Use this with the -P option to clear the existing gamma ramps + before applying the new color temperature. + + -p + Print parameter and exit. + + -P + Reset exiting gamma ramps before applying new scolour effects. + + -r + Disable fading between colour temperatures. + + -t day:night + Colour temperature to set at daytime and at nighttime. + + -v + Enable verbose output. + + -V + Show program implementation and verison. + + -x + Remove adjustments from screen. + +OPERANDS + None. + +STDIN + Not used. + +INPUT FILES + None. + +ASYNCHRONOUS EVENTS + redshift takes the standard action for all signals except: + + TODO + +STDOUT + TODO + +STDERR + Default. + +OUTPUT FILES + None. + +FILES + TODO + +EXTENDED DESCRIPTION + Gamma ramps + redshift applies a redness effect to the graphical display. The + intensity of the redness can be customised and scheduled to only be + applied at night or to be applied with more intensity at night. + + redshift uses colour correction lookup tables (CLUTs), usually called + gamma ramps or gamma correction ramps, to apply this effect. + + Colour temperature + The redness effect applies by redshift is modelled after black-body + radiation, specifically with a 10 degree observer. Although black-body + radiation starts at 0, redshift's model start at the conventional 1000K + (1000 Kelvin). For this reason, no colour temperature below 1000K can be + specified. However, as there is a limit can be determined for the colour + when the colour temperature appreciates infinity, the upper limit for + allow colour temperature is instead determined by the data type it is + stored in. However, it also means that it is meaningless to use colour + temperatures above 40000K. + + The sRGB colour space, and modern monitors, use the standard illuminant + D65 as the reference for pure white, modelling ideal day light. The + correlated colour temperature of D65 is called 6500K, however it's + actually 6504K, but redshift's defines this illuminant has having the + colour temperature 6500K. This means that 6500K is the neutral (no + effect) colour temperature. + + The current version redshift assumes the monitor uses sRGB. However + this is usually only true for CRT monitors. HDR-capable monitors + particular diverges significant for sRGB. This means that the display + colour does not perfectly correlated to the specified colour temperate. + Lower (more red) colour temperatures, about 1900K and below, are out of + gamut, and thus incorrect even on sRGB monitors. + +EXIT STATUS + TODO + +EXAMPLES + TODO + +KNOWN ISSUES + No or incorrect effect on cursor + Some graphics drivers apply the effect (colour corrects) twice or not at + all on hardware cursors. It is often possible to reconfigure the display + server to use software cursors, to avoid this problem, however at mouse + pointer performance cost that may be noticeable on very low-end computer. + + D65-flashes + For some versions of some graphics drivers, there will be an occasional + flash where gamma ramps are not applied to the output. + + Limited hardware support + Low-end hardware, especially embedded devices, often lack colour + correction features redshift abuse to apply it's affect. redshift is not + always able to tell if support is missing. + + Limited software support + redshift does not yet support Waylaid. If your environment contains the + variable WAYLAND_DISPLAY, you are using a Wayland compositor and cannot + currently expect redshift to work. Even with Wayland support, it would + be up to each individual Wayland compositor to opt in to support + applications like redshift. + + Backlight control + redshift uses gamma ramps rather than backlight control to adjust + brightness. This actually intentional and for your best. Most + contemporary monitors require Pulse-Width Modulation, which causes + flicker than can cause eye-strain and headaches, to adjust backlight. + Using gamma ramps is a safe option, it's also considerably less work + basically no extra code and posses no additional limitations. It's often + not possible to adjust backlight on desktop monitors from software, for + devices for which it is possible (mostly telephones and laptops, however + not all have fine-grained enough configurability to be usable) it's not + possible from software to determine well enough how changing the + backlight settings changes the backlight physically. If you still want + backlight to be controlled, you can hook in a tool such as + adjbacklight(1). + + Flickering and temporary suspension + redshift uses the gamma ramps for the monitor to apply it's effect. The + gamma ramps where originally intended for colour correction. Therefore + there is no standardised why have multiple applications applying + different effects without overriding each other. This can cause + continuous flicker if multiple instance are running or effects + temporarily disappearing. By default, redshift uses coopgammad, which is + a daemon applications can opt to use instead of directly setting the + gamma ramps themselves, coopgammad can then calculate the result of all + of the effects and apply them as one, allowing the user to use multiple + applications that apply different effects. However coopgammad still has + to compete with applications that does not use it. + +RATIONALE + To prevent the user from accidental making the screen black, brightness + level below 0.1 are forbidden. + + To prevent colour distortion and making the screen too white, brightness + level above 1.0 are forbidden. + +NOTES + "Colour temperature", or just "temperature", is actually short for + "correlated colour temperature". (Your monitor is not a black-body + radiator.) And specifically the correlated colour temperature of the + monitor's whitepoint. + + It's common for users to miss to specify a coordinate as negative, + which, if missed on the longitude can swap day and night. The latitude + is negative on the southern hemisphere and the longitude is negative on + the western hemisphere. + +SEE ALSO + cg-tools(7), coopgammad(1), radharc(1) |