Colour casts

Good evening,

At the risk of seeming very stupid, are colour casts noticable by a keen eye or are there more technical ways to tell if the image has a cast. I posted an image that only a couple of people mentioned a blue cast but not others. The cast was really obvious when I put the image back into PS, but to my eye, initially when posted, it wasn't obvious.

Any help appreciated

Graeme, UK

They are certainly noticeable to a trained eye. Our minds often compensate for casts subliminally so it does take some deliberate effort to notice them. Once you become aware of them and the conditions in which they occur though - you will see them every time.

Guy

My wife has a terrific eye but I sturggle. My crutch is the white eyedropper in Photoshop's Levels. Click on something that should be white in the image and watch for a change in the preview. Click it back and forth a few times and any color cast will seem to flash like neon. It's helped me train my eye, so at least I'm finally getting better.

It is definitely a case of practice. Try to keep the room lighting at a minimum, to avoid introducing an external color from the room lighting or furniture reflections. Also, if you are using a CRT, let it warm up for 20-30 minutes before doing serious work. The last probably won't make a huge difference, but it won't hurt.

Just be sure you are starting with a calibrated monitor. Without that step, you don't have a chance of getting it right.

Hi Graeme,

Most people don't see the colour cast until it's pointed out to them . You can train yourself to spot them quite easily and the conditions in which you take the shot will sometimes give you a clue as to the presence of a cast - for example, most shots taken in the UK in winter will tend to exhibit a cool blue cast, except when the sun is shinning strongly. As you're used to the light in the UK, you tend not to notice the colour cast so much as you think it is normal!

You can check various parts of an image for the presence of a cast. Most image processing programs now have some sort of RGB colour readout which shows the separate RGB values in an area under a cursor. If you can find areas in your image that you know should be black, white or grey, then you can check the colour readouts for these areas to see if a particular colour is high or low (the values of each channel should be close together if there is no cast present). In Photoshop, you can use the Eyedropper tool and the info pallette to check the colour values. An added benefit of using PS is that you can also see the Cyan, Magenta and Yellow readouts too which can help indicate a colour caste in one of those colours.

Thank you gents....

Nick, that works a treat. I am cured and a lot happier!!

Hi Graeme
As already mentioned the key seems to be a trained eye. It's a good skill to learn but also a bit of a curse because once you learn to see colour casts you'll see them a lot.

You've been given some good suggestions here for how to learn to see them. Have fun

I see what you mean Ed. Everything seems to has some kind of cast!!!

I created some printer calibration images years ago with Photoshop that contain a number color squares with increasingly unbalanced color from neutral. Also useful for evaluating a monitor though monitor calibration tools are the standard these days and I use a Monaco product. Very easy to create with a bit of Photoshop skill. One starts from a white 255,255,255 background by making a matrix of narrow black line delineated squares. Then use the Color Picker to select offsets which are used to color fill individual squares. The first column of primary and secondary color squares would be 255,254,255 and 254,255,255 and 255,255,254 and 255,254,254 and 254,254,255 and 254,255,254 with the second column 255,253,255 and so forth, with the third column 255,252,255 etc. Now if your monitor or ambient lighting is causing a color cast, the white 255,255,255 background won't be neutral while one of these other values might. The same check can be done lower down on the gray scale say at 200,200,200 though is most easily seen at peak white. One may also be able to see hues like a subtle red that looks too green making yellow. ...David

The easiest way to find out color casts is to fully saturate your image....if the whites or blacks get a color...BINGO you have a color cast....

Note that a colorcast sometimes can add to an image...so there is not always a need to fully get rid of them.

I've always used Jasper's method. Just crank the saturation up to 100% and you'll notice if there's a color cast.

Ah , thank you very much indeed. Steep learning curve this business!!!



Graeme

Graeme now that you're learning to see colour casts, be aware that looking in the mirror on the morning after the night before can be disturbing. Especially if the wine was flowing freely.