You’ll be amazed how your photos can be transformed with proper tonal adjustments, adjustments that are a lot simpler than you might have thought. Once you discover how to play the powerful curves tool in your photo editor, your images will sing.
What would you do with this image? It’s flat, all grays, no blacks, no whites, no contrast. I took this picture on an overcast, shadowless day. The negative was developed in Diafine, a compensating developer that yields lower contrast negatives. A double whammy.
Not to worry. Flat negatives scan better because the scanner has an easier time grabbing midtones. All the information is there in the scan. It’s simply compressed and needs to be coaxed and prodded with tonal adjustments using the curves tool.
Here’s the transformed image. Quite an improvement over the flat, lifeless scan. I expanded the tonal range and increased the contrast using the curves tool in PWP (aka brightness curve). Once I was satisfied with the tonality of the image I used unsharp masking (USM) @ 10%/r=30/threshold=0 for local contrast enhancement. Then I sharpened again with USM set @ 50%/r=2/threshold=0.
I downsized the image for the web, saved the file and reopened it in the GIMP where I tweaked the levels and used smart sharpening with very low settings: amount=30%/r=0.3/threshold=0. When you downsize an image, sometimes you need to sharpen again to compensate.
Let’s go through the tonal adjustments step by step. This screenshot shows the raw scan on the left, the transformed image on the right. The brighness curve dialog (lower left) shows the original histogram with a superimposed S curve. The original curve is the straight line rising at a 45 degree angle from lower left to upper right.
I established three control points along this curve and moved them to create the new S shaped curve. The dialog in the bottom center is the same curve but with the histogram view selected. You can see how I slid the bottom of the two double arrows to the left for the shadows and the other arrow to the right for the highlights.
All images will have a characteristic curve that rises gradually from the foot, steepens through the midtones and rolls over the shoulder at the top. The steeper the rise, the more contrast. The S curve for each image will differ somewhat. The trick here is to massage that curve until you like what you see.
The dialog on the bottom right shows the histogram for the adjusted image. It’s still on the dark side. I tried making all the adjustments using one curve, but got better results when I did a second transformation on the highlights.
The image on the left is the transformation from the first screen, the image on the right shows the final.
This time around, I used two control points to anchor the shadows and two more to give the highlights a boost. Once again, the dialog on the left and in the center are two views of the same curve transformation.
The dialog on the right shows the final histogram. Note the shape and how the original histogram has been expanded to fill all the values from pure black to pure white.
The title of this tutorial is B&W Photography: 16-bit Tonal Adjustments. Now I want to show you why it’s so important to work with 16-bit files. A 16-bit file can contain 65,536 discrete tones ranging from pure black to pure white. An 8-bit file has only 256 values to work with.
I converted my 16-bit scan to 8-bit for this demonstration. I went through the exact same transformations as I did with the 16-bit files I showed you. When you expand the tones of a flat image, you are stretching the histogram with limited tones to cover all the values from 0 to 255. Have a look at the histogram on the lower right. All the gaps are missing tones — not a good thing at all.
And the gaps get even worse here. Compare the final 8-bit histogram to the final 16-bit histogram. Big difference. I used an extreme example and not all images require as large a tonal adjustment as this one, but when you want to make a lot of tonal adjustments (or even a few small ones), use 16-bit files whenever possible.
So now what? Try the curves tool on your photos. Play with curves and learn how to use them effectively. It just takes practice (and patience). You’ll learn that sometimes small tonal adjustments are all you need to really transform your images. Next time, I’ll show you a more subtle example.
Feel free to leave comments and questions. I’ll be happy to answer and help where I can.