Calibration for Image Mastering
"Colour management doesn't mean squat if your audience is on cell phones and un-calibrated home screens."
The above is a fairly common comment regarding display calibration when performing grading or mastering.
Unfortunately it is this lack of forward thinking that causes a number of major problems with later viewing of material on any display.
If you do not care about accuracy during the image generation, the results will always be bad - on any display, regardless how well it is calibrated - or not. Two wrongs can never make a right, while a right and a wrong will always lessen the final wrong.
If your grading display is crushing blacks, and is too blue it will cause you, the colourist, to lift the blacks to overcome the crushing, and make the image too warm to counter the inherent coolness of the 'blue' display. So when the graded images are viewed on a correctly calibrated display the result will show the inaccurate grading, while things will get much worse if the final viewing display has lifted blacks, and is too warm, as the images will show grey blacks with washed-out detail in the shadows, and a very inaccurate colour temperature.
When mastering, if you always work on a well calibrated display the worse any final error can ever be is just that of the un-calibrated viewing display, and as the viewer is used to seeing image on that display - most of which will have been generated on reasonably calibrated displays - they will be able to judge by reference the quality of your images - a direct comparison to what they are used to seeing.
If you have graded on a poorly calibrated display their relative judgement on their still uncalibrated/inaccurate display will define your images being yet more inferior.
That is the definition of a poor workman, with a poor workflow, and is something all professional will always strive to avoid.
A 'relative' comparison is just as valid as a definitive comparison, as it will always show the original material to be inferior.
This is also why a colourist must never deliberately alter a grade for viewing on an uncalibrated/inaccurate display, no matter what any unknowledgeable client/producer may ask for. Altering a grade so it becomes inaccurate on a calibrated display will show as being yet more inaccurate on any other uncalibrated/inaccurate display, as the 'relative' comparison to other accurately graded material will make the deliberately altered grade appear even more 'wrong'...