Join Taz Tally for an in-depth discussion in this video Evaluating the image, part of Photoshop Color Correction: Extreme Color Cast.
Well, looking at this image and regardless of whether you look at the histograms or not or, how badly out of calibration your monitor is. You can probably see this has a pretty strong blue-green colour cast. this is an image of a white tip green shark, that I shot while diving in the Riven reefs in the northern portion of the great barrier reef of the east coast of Australia. And these sharks are fairly common in this area, and this type of deep blue green colour cast is very, very common when you shoot underwater. In fact, the deeper you go, the more blues and the less reds and yellows there are.
And that's because the hydrogen bonds in the water that holds the water molecules together preferentially absorbs the warmer wavelengths, the reds and the yellows. So you get this blue green very, very commonly and as you get down deeper and deeper even the green begins to disappear and you mainly get blues and purples. So a big strong colour cast in this image and also to, visually it's not really all that great a contrast. And, we're not quite sure whether that's due to the blue, or if maybe we're kind of missing. We'll to get the detail story, or as Paul Harvey would say, the rest of the story.
We look over here on the histogram as always. And let's first set our master histogram to RGB just to look at the tone as we always do. And we can see where most of the data is in the quarter tone to three quarter tone. Alright, there is data in the near highlight. There's a little bit of a peak on the very whitest end, but not much data right in here. This is mostly flat noise, and then on the shadow end, from about three quarter tone to shadow, there's not much data at all. So we can see that's a good portion of the reason why this image has somewhat low contrast is, is really ma, not much three quarter tone or shadow data in this precious little data over here in the true highlight.
Alright, and then when we look at the individual histograms, we see, you know, the real challenge, and let's go ahead and view this as colours. So we can see the overlapping histograms as well as the individual ones. And it's very clear no matter where you look that blue is way offset to the right. The green is offset less and then the red is offset, well, the least. It has the least amount of data in the image and it's mostly in the shadow portion. So, we have a very strong colour cast. And this is a very typical histogram for images that are shot underwater. So if we can correct a really strong colour cast like this, using the histogram based colour correcting technique we've been using, we know we're doing something right.
So let's go see if we can do that, and, at the same time, we'll see if we can fix that contrast and improve the contrast a bit as well.
Check out the first installment in this series, Photoshop Color Correction: Fundamentals, for more detailed information about adjusting color in Photoshop.