Luminosity Blending in Photoshop
Welcome back all right so I wanted to talk about uh luminosity blending because um again what we're concerned with here is ah the lights and darks in the image so I'm gonna illustrate of the concept here using this very colorful shot and in our in luminosity blending approach to tonal control we're going to be thinking of our color images in black and white so it's useful to know howto do ah ah black and white conversion this this particular images very colorful but we can still think of it as it would be in its um different channels in different color spaces so uh this image could be rgb it could also be seen like a and it could also be l a b and in all three of those different color spaces they have a different grayscale channel structure so when we look at this in rgb the road at the top here groups where they took over my computer are we okay? We're in uh he's importing you gotta love this life I'm going to take over the computer again here live while it's doing this important job ...
go back to my keynote um so let me have it let me have it don't fight me um so again top row red green blue these are radically different grayscale renderings of the same color image the second rowe is leiby lightness and then a and b and you'll notice they have even again radically different grayscale renderings of the same image cy in magenta yellow and black at the bottom and when we think of converting into black and white it's useful to remember that the same image could be represented and rg being seem like a and b and sometimes we could kind of blend uh uh information from all these different channels to create a a complete a new black and white rendering of the image so if I if we're done now with our importing I'm gonna actually let me let me finish this up here sorry. Um the idea here this is the regular color image and manipulating these grayscale channels which I want to go into photo shop here in a minute actually look at the same image before we get to working with bernard uh I can I can create a version of this color version of this image that is radically different using the grayscale channel so we can make it look like this and, um let me show you that get into in the photo shop here. We're still importing our pictures, so here we are from yesterday it closed these out on I'm gonna open up my sunflower image with any luck here, all right, so again remember I was saying this could exist in multiple colors spaces right now it's an rgb so we have read green and blue and there's enough information here that we could do some interesting things to do. A black and white conversion. Um, there's always the black and white tool. So if if I made an adjustment in black and white, um, the default here, of course, for this particular images dreadful, right, but weaken work the different colors of the image on these sliders, you know that that the pedals of this flower yellow and I can brighten those up just by moving the yellow slider a bit. Here. I can also, like dark and the blue, uh, using the blue slider. And so, you know, I can get kind of maybe almost an infrared sort of look out of this image. There's. One problem, though, with the black and white, uh, conversion adjustment. Okay, they're black and white adjustment photoshopped, which is a fairly new, ah adjustment type. And I'm just going to point out this area down here. There's there's sort of like a little white edge all the way around this leave. And this is a defect in using this approach when you use ah, strong sliders settings. Um the transition between the greenleaf and the blue sky is a little posterized right at this edge so that we're getting this little funny little uh white line I'm gonna turn that off for a moment and duplicate this image so that we have another copy because I'm going to compare compare them in a minute so here's my black and white conversion I'm going to do black and white conversion here different um so we can also use the channel mixer adjustment and that gives us some access to the actual red green and blue channels this tool has presets er and the presets are all designed for black white conversion so if for instance we could say give me the black and white with the red filter and what we get is exactly the look of the red channel by itself and you can see here one hundred percent read but we can also mix between the different channels so I can put fifty percent here and fifty percent in the in the green and uh now I've gotta blend my blend adds up to one hundred percent so all of these presets here respect this sort of hundred percent total which does not distort the overall luminosity the image however you can cheat so and especially in this image we can very easily subtract the brightness in the blue channel and I can make this blue sky very dark and get very similar look that I got with the black and white adjustment to the look at the difference along the edge so here the edge of the leaf against the blue background that's that's a natural edge? I'm not getting an artificial halo, which is something that I get when using the black and white adjustment tools, so that is the one big difference and the thing to look out for the black and white of justin tools very easy and a sort of intuitive you just darken the color is dark and the light in the colors in the image, but you can generate sort of artificial results with it very easily. Lee blending the channels is much more natural and they but they blend better, so something to be on the lookout for. So we've used the channel mixer here, too blend these channels, but we can also do something, uh a little more trick, and it still involves blending the channel, so I'm going to throw away this channel mixer adjustment and again inside this color image, we have three black and white images the red channel of the green channel in the blue channel so here's here's ah here's something that people don't often do or even know about in the channels panel if I come over here to my options, my fly away options menu, I have something called split channels so if I select split channels, what happens is the image is broken apart now into three grayscale documents and labeled appropriately so this is now a a grey scale document that represents the red channel, a separate document, the reference, the green channel and a third document that represents the blue channel. Okay, now weaken blend these in layers because I have three separate documents, aiken reassemble them so that they stack up in layers so let's, take the green document and I'm going to drag it on top of the red document. Ok, so this is sometimes difficult for people. We were doing this a little bit yesterday, uh, but I'm taking the move tool I click inside the image and hold down the shift key and drag up to the tab that represents the red document. I just sort of wait over that tab till it comes forward, and now I'm still holding down on the mouth, dragging it until I've got the cursor over the image I let go of my mouse while holding the shift key down, and it drops the image in perfect registration on top of the other image. So I've got the green document on top of the red document, okay, it's a little bit sort of like, you know, rubbing your belly and patting your head so there's always this coordination thing which finger do I let loose of? And you know, s o may take a little practice for you to get that um anyway, holding down the shift key is the secret that makes these things line up when I dropped him on top of each other and so if you try it and they don't line up it's it's because you let go the shift key okay, so here I have the green I'll go ahead and label that green on top of the red and I can change the opacity if I change the passage of fifty percent. I've got something similar to what I did with the channel mixer where I had fifty percent read and fifty percent green but it's in a in a layer uh now, because it's in a layer, I can do something even more interesting to blend these two different grayscale renderings to blend them together because I have the power of the layer apply moz to play with instead of just simply luminosity. I'll leave the the capacity up a one hundred percent and I'm look, I look at these two just talking back and forth a look at the green and the red and think to myself, I like that dark sky of the of the red document, but I've lost all the detail in the pedals here and there pedals are a little darker here in the green document. Gee, wouldn't it be great if I could yet just the darker pedals and keep the dark sky and that is actually incredibly easy here in photo shop? We can just change from normal apply mode to darken and magically the only thing in that green layer that can make the underlying image darker is the pedals in that in the green later everything everything else in the green layer is lighter than the red underlying later ok, so I've blended them and I haven't had to mask it or do anything fancy like that now if I want say, you know, the center of this flower seems to be a bit quite a bit darker now and it is darker in the green channel, maybe I want that the lighter one from the underlying layer well, I can mask it because is layer I can apply a layer mask so I'll go ahead and add that layer mask there and I can paint into that layer mask with black I'll just make a nice big brush here and now I'm hiding the application the dark and application of the green layer to reveal the lighter sunflower center from the red lair okay, so we've used red and green and now probably everyone out there is wondering, what am I going to do with this god awful thing uh, in this particular image, there's like no blue in this flower with green and the yellow really don't have any traces of blue, so the only brightness in this channel or this layer, this document is in the sky, so but I am going to use it. In fact, I'm going to invert it. So do command I or image adjustment invert so now it's the exact opposite of itself, and I'm going to do in my trick again. Hold down the shift key is the move tool and drag it up to that red tab moved back down and let go the mouse while holding on the shift key, and I've dropped it on top. Now what if I change the planeload from normal to multiply here? Well, now I'm back to that kind of infrared look because in multiply everything. If it's white, it has no effect on down the line layers it's only where it's darker than white, that it has a corresponding effect and I'm darkening everything with the dark sky so in normal, right? And the only thing dark and this layer is, is the sky changing to multiply? And I'm adding that darkness into the underlying layers, but because it's a layer I can again at a layer mask and what would happen now if I put a grady in't into that layer mask, and I'm gonna. I'm gonna put a black to white grady in here, starting with black at the bottom in a drag up. And I'm holding down the shift key to constrain that action of that great and so it's. Perfectly perpendicular. I'm just going to ramp this grading through the image. And now I've got I've got a graduated filter effect, sam, just darkening the top half of the sky. This is now completely new, black and white rendering of this image that took advantage of all three channels red, green and blue, but combined them and completely unique way. And I have achieved a result here. That would be really different than just doing a black and white conversion and using a curve.