Images converted to black and white are tinged with pale cyan

[OutDamnSpot]

I convert from colour to black and white often.  It usually works, but occasionally, some images are tinged with pale cyan instead of just shades of grey.  

For example, 255, 255, 255 produces white, as expected, but 244, 244, 244 produces pale cyan instead of pale grey.  The CMYK values are 3%, 2%, 2%, 0%, so the pale cyan is not surprising.  I'm using the sRGB colour profile.  It there an easy way to ensure I get C=M=Y, and greys that are grey?

[davescm · Accepted solution]

Forget the CMYK values. You are working in RGB colour. If your conversion to black and white is giving you pixel values where R=G=B then it is working correctly. So that leaves your monitor.  Photoshop is colour managed which means it uses the monitor profile in the operating system to adjust the colour values sent to the screen so that they display correctly. That of course relies on that monitor profile accurately describing the behaviour of your monitor. To get that fully accurate, we use hardware calibration and profiling devices, such as the i1Display,  to read the individual screen and ensure that the resulting profile is accurate. Adjusting any screen controls such as brightness or contrast invalidates that profile and it must be made again. If you have a broken profile then it can cause issues with the display. If you are serious about colour then a profiling device really is an essential part of your kit.

If you suspect a broken profile in Windows you can go to Windows color management and temporarily change the display profile to sRGB until you can make a profile for your individual monitor.

One more thing, most displays-are 8 bit colour which limits the number of steps. This can cause light banding in gradients where the greys do not track exactly. This is a display artifact and does not change the image itself.

Dave

[Derek Cross]

There are a number of ways to convert a colour image to grey, try this:

Open your  colour  RGB image then select: Filter > Camera Raw Filter, then select Monochrome from the Profile drop down.  You can then use the various features, such as Exposure and Black and White mixer to fine-tune your image to your heart's content!