Over the years I have been asked a lot of questions about how I manage to get so much detail out of the highlights on my film scans, particularly color negatives. A lot of people have also been asking how I correct the colors in my scans. I touched on the basics of those topics on an earlier post, so if you haven't already read my blog post on Scanning and Editing Color Negative Film make sure to check it out. This post will elaborate on the topic of luminosity masks, and how I use them for both color negative and slide film. At the end of this post, you will also find a downloadable Photoshop action that will easily create luminosity curves layers for both the highlights and the shadows so you can try it yourself. (Don't worry, I won't be offended if you scroll to the bottom to get that action now) Before we get started, I will say that this is not necessarily the only or the right way to make luminosity adjustments. This is just an overview of my workflow and a process that has worked well for me. These same ideas will also help with your digital images so I hope everyone learns something!
Image without luminosity adjustments, roll your mouse over the image to see it with the luminosity masks
On the image above we're going to look at a type of scene that I commonly get questions about: shooting right into the sun and still having the sun and foreground nicely exposed. First of all, there's a lot of magic happening in the color negative films like Kodak Ektar and Portra, especially the latter. The dynamic range is outright insane on these films, being able to capture all the detail from the foreground to the disc of the sun. The problem is that once you scan an image that contrasty in, it will look very flat if you try to maintain details in all areas of the image. You still don't want to clip any of the highlights while scanning because we want to have more precise control over that in a program like Photoshop. Luminosity masks will give us the edge we need to adjust areas of the image based on their brightness, or luminosity. This way we can bring up the foreground brightness and contrast while only barely touching the area around the sun in a way that is subtle and creates no halo effects.
Ok, so what the heck are luminosity masks anyway? I had the chance to visit the gallery of well-known large format landscape photographer Michael Fatali several years ago. He's one of the few who still projects his images onto massive sheets of cibachrome paper and makes real darkroom prints from color transparencies. It's a shame to admit that I have come into the game of film photography too late to be able to master the art of cibachrome printing. There's only a few people left that have purchased the last of the paper, and even they have just a few years' supply left. Anyway, when talking about his printing technique Fatali mentioned that he makes multiple exposures of a color image on black and white film as well. He will then line these black and white negative images up perfectly with the original positive slide, essentially creating a luminosity mask in a traditional darkroom environment. That negative image blocks the light from the brightest part of the slide and allows light through the darker areas, essentially allowing him to raise the brightness of just the shadows. Absolutely brilliant! We are going to accomplish the same task in Photoshop with just a few presses on the keyboard.
Alright let's get to it! There are a few different ways you can select the highlights of an image, but my favorite way is to press Ctrl + Alt + 2 (Cmmd + Alt + 2 for you Mac users). Once you've pressed this you'll see the selection outline all over the image, similar to the photo above. Pixels will be selected based on their brightness, with a pure white pixel being selected 100% and a pure black pixel not being selected at all. Everything in between is selected proportionally based on its brightness. Once you have this selection, I like to start by making a curves layer with it by going to Layer>New adjustment Layer>Curves on the top menu. Now you have a curves layer that will mostly just adjust the highlights in the image. I then Ctrl+Click on the curves Layer (click on the little photo just to the left of the word "curves") to get the same selection again and inverse the selection by going to Select>Inverse on the menu at the top. I then make another curves layer just as I did before with this selection, only now it will mostly adjust only the shadows. You can also do this entire process in one easy click by downloading my super handy Photoshop action at the bottom of this page.
Important note for film users: You will want to clean up all dust spots on the image before making these luminosity masks! Think about that black or white dust speck in the sky not being selected by the luminosity selection, then making adjustments to the highlights and creating a tiny area that will not go away when you use the healing brush tool unless you go through all your layers to remove it. It's nothing but sadness, so make sure to take my advice here!
Ok, so now we have these two awesome curves layers, but what can we do with them that helps with your film scans? I like to start with the shadows layer, which is the one that looks like a negative image when you Alt-click on the layer icon. The curves adjustments you can see above are rather typical to what i would do on any of my images. I go through each of the color channels in the curves layer and bring the black point over until it would almost clip. This has effectively removed any of the common color cast you would get in the shadows of a scan. The blacks should already look much more pure and not a mess of noisy deep grey. This has likely made the image darker than you'd like, so now I head over to the RGB channel and bring the brightness back up and typically also add some contrast to the shadows with a gentile "S" to the curve. Then I go back and fine-tune the colors with the individual channels.
I use the highlights layer to get the sky to look exactly the color I want, usually making much more subtle changes than the shadows layer. I start with the RGB channels and move the right slider almost until the highlights clip. You can check for clipping by holding the "Alt" key as you slide the black or white points and the bottom of the curves adjustment. Since this scene was shooting into the sun, I couldn't really move the white point over as it would clip right away. Instead I added a bit of contrast to the highlights with an "S" shape curve that's particularly high towards the top. The dynamic range of color negative films like Kodak Portra is downright insane, especially for images shot into the sun. While the film can handle the exposure of the sun with the rest of the scene, I think it will look unnatural and flat if you leave it that way. I feel it's best to carefully adjust the highlights in this way to brighten the sun and the area around it without destroying the feeling of bright, glowing light and the orb of the sun. From there I tend to make some very minor adjustments to color in the highlights. This was a bit of an unusual scan because I often find myself adding blue in the highlights but to bring this image closer to my memory I had to remove blue. Every image takes a unique approach.
Image without luminosity adjustments, roll your mouse over the image to see it with the luminosity masks
I've talked very little about how I edit my slide film scans, mostly because they don't seem to need as much color correction and I get far less questions about slides. I still think luminosity masks play a big role in getting the colors right, mostly in the shadows where scanners tend to reveal nasty colors casts unique to each type of slide film. Mouse over the image above and you can see how big a difference this process makes. For this image I've chosen a classic scene where a scanner will struggle in the shadows: a nicely exposed sheet of Velvia 50 taken during a sunrise with strong alpenglow colors. Similarly to the way I scan my negative film, I make sure to leave a huge amount of room on both the highlights and the shadows during the initial scan. This results in a very flat image where no detail is clipped. While the sheet of film may look beautiful on a light table, the scanner produces results that are often less than flattering. Luminosity adjustments are my starting point in getting the contrast and colors correct.
Being able to adjust the colors in just the shadows has been a game changer in the way I get my colors correct on slides. Looking at the curves adjustments above you can see I make some major adjustments depending on the film type. Velvia 50 will have a good amount of red in darker areas of the image, where Provia 100f will have tons of blue. Velvia 100 is well known for its extreme magenta cast. Just as I did with the color negative film, I will start going through the individual color channels and adjusting the curves until each channel almost clips to black. Then I add some brightness to the shadows with the RGB channels.
As a quick tip, remember to hold Alt while adjusting the black point of each channel to make sure you're not clipping anything. The image will turn the color of the channel and any clipped areas will appear in black. This works for highlights as well.
As far as highlights go, slides don't typically need a whole lot of adjustment here. I just brighten the image up until it almost clips and make very small adjustments to colors and contrast. That's pretty much it for my luminosity mask adjustments. If I see a particular part of an image that needs extra adjustment I may mask out the rest of a new layer with the paint brush or gradient tools. You can even get creative with your luminosity adjustments, using them to apply hue/sat layers only to shadows or highlights or any adjustment you could really imagine. Of course luminosity masks aren't the only part of correcting the color and contrast, but they are one more tool you can use to get you closer.
You may ask why I would use luminosity masks to correct color instead of a global curves layer. My response is that it gives me just that little bit of extra control over the image outcome and doesn't take a whole lot of effort. I'm also using medium and large format film so I tend to already be very picky with the images I expose, might as well put all the effort into each image that you can. Being able to remove unwanted red casts from the shadows while still leaving pleasant film tones in the highlights is a very desirable feature to me. You have any other questions for me regarding luminosity masks? Feel free to leave a comment and don't forget to download the easy Photoshop action below!
Thanks for looking! I hope this helps some of you out there!
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