Quick Tip: Straighten Up!

One of the easiest photo flaws to fix is a tilted picture. A horizon that's not quite horizontal or a vertical line that's not quite vertical can distract the eye away from the subject of a photo. So fix it!

Yikes. (Intentionally tilted in software for purposes of illustration.)

Most image editing programs will have at least a rotate function. You can use this to eyeball a correction. Or--my favourite--if your editing software allows, you can simply find a line in the photo that should be horizontal or vertical and, using the appropriate tool, drag your mouse along this line. The software will then do the rotating for you. Here's how to do it in my favourite software, darktable:

Open your image. In the right hand panel, click over to the basic group (the circle button), and then find the crop and rotate function. Select this function. Place your cursor at one end of a line that should be either horizontal or vertical. Right-click and hold, then (while still holding the right-click button) drag your cursor along the line to the other end. Release the button. darktable should automatically rotate the image for you.

If you're having trouble getting it just right, you can try zooming in to 100% or 200%. I find this often affords a more accurate correction. In this example, I'm using the shore as a guide, zoomed in to 100%:

Straightening a horizon in darktable. Click to enlarge.

Don't let your photos suffer from crooked horizons or diagonal verticals! Your viewers will thank you.

Behold! A (more or less) straight horizon!
18mm (~28mm equiv); 1/250 @ f/5.0, ISO 100

Photo Editing Techniques: Levels

Today I'm going to talk about a simple but powerful way to change the appearance of your photos: the levels tool. This post may look long, but that's because there are a lot of images--don't be intimidated! This is fairly easy stuff that can make a huge difference in your images.

The levels tool can be found in most image editing programmes (including my favourites, darktable and GIMP) but for the purposes of demonstration, I'll stick to using darktable only. I will also be using a simple image containing various tones to demonstrate the effects of levels adjustments. I encourage you to download this image and play with it on your own; the easiest way to learn is through hands-on practice:

Right click and save as to download to your own computer.

 The basic anatomy of the levels tool is a box containing the histogram for your image, with a black-to-white gradient at the bottom and a set of three sliders. The levels tool in your software of choice may look slightly different, but it should function similarly. In darktable (and in many other editors), you will also see three eyedroppers; these allow you to move the position of the sliders more precisely (more on that soon).

If you're familiar with your luminosity histogram, the levels tool will probably be reasonably intuitive. The gradient at the bottom represents the distribution of tones in your image--it's sort of a guide to reading your histogram. On the left, you have your darkest tones, in the middle you have your midtones, and on the right, you have your lightest tones.

Adjusting levels in darktable. Click on the image to see full-sized Note that the histogram at the top of this screen capture and the histogram in the levels tool are the same, and represent the distribution of tones in sample image shown at the beginning of this post.

The sliders are used to tell your image processor which tones in the original image should be rendered as pure black, which tones should be rendered as pure white, and where your middle grey should be positioned. Their default positions, therefore, will be at the far left, the far right, and the middle of the histogram respectively.

If you slide your black point slider to the right, the amount of black in the image will increase--anything that was darker in the original image than the new position of your slider will be rendered as pure black. Note that the middle slider will automatically be repositioned in the exact centre between the new black point and the white point. Note also that the histogram for your image (at the top right of the screen) will also change to reflect the new tonal distribution:

Changing the black point (and with it, the mid-point).

 Likewise, if you move your white point slider to the left, all of the tones in the original image that are lighter than its new location will be rendered as pure white. Again, the midpoint slider will automatically reposition itself to the centre between the black and white points:

Moving the white point.

Moving the middle grey slider is a little trickier to explain, but basically, the slider determines which original tone will now be rendered as middle grey. Therefore, if you move the slider to the left, your overall image will lighten (although your black point and white point will not be altered unless you choose to move them), because you are telling your editor that a tone originally closer to black should be lightened to midgrey, and therefore the other tones will also lighten to reflect the new distribution of tones. If you move the midpoint slider to the right, the overall image will darken, as you are telling your editor that it should darken what was originally a lighter tone into middle grey. This is easiest to understand by playing around with the sliders yourself.

Lightening the image by shifting the midpoint.

If you want to precisely place the black point, white point, or midpoint, you can use the eyedroppers. Simply click on the eyedropper associated with the point you wish to change, then click on the area of the image that you wish to place at that point.

So how does this work in colour? Let's play around with two examples. First, a colour distribution:

I encourage you to also download this image for practice.

Let's try moving the black point...

Shifting the black point.

...and now the white point...

Shifting the white point.

...and now the midpoint...

Shifting the midpoint.

...and now all three points:

Shifting black point, midpoint, and white point.

See how the levels tool can dramatically alter the look of your image?

Finally, let's play with a real-world example:

A Nova Scotian sunset.

See what happens if we shift the black point?

Moving the black point.

What about if we shift the white point?

Moving the white point.

And finally, what if we move the midpoint?

Moving the midpoint.

The levels tool is just that simple. And, to make life even better (at least in darktable), adjusting your levels will adjust your image in real time, letting you tweak it exactly to your liking. It's an easy tool that makes a powerful difference.

Raw Processing: Introduction to darktable

As I mentioned in a recent post, I use the program darktable for the bulk of my raw file development (and I plan to use it for file management, when I get around to actually, y'know, managing my files). I thought I'd give a brief overview of the program for those who might be interested in getting a taste of it without committing to an installation, or those who have recently installed it and find themselves completely lost.

 

darktable for Windows: lighttable

This is something like what you'll see when you open darktable, provided you have imported files into the program already. This is the lighttable section of the program.

On the left panel, you have options to import files and folders, view imported images (filtered in a variety of ways depending upon user instructions), see recently used collections of images, and see the image information (such as EXIF data and file location) for the photo you have selected in the central panel.

In the centre panel, you'll see a variety of images. The particular images you will see will depend upon the selections you make in the left panel. You can further filter the displayed images with options at the top and bottom of the panel. Also in this centre area are display options and access to global preferences (click the wheel icon).

(Quick tip: if you hover your mouse over a photo in the centre panel and hold down z on your keyboard, the photo will be enlarged until you release z. If you hover your mouse over photo and hold ctrl+z, the photo will be enlarged with indications over all areas that darktable detects as being in focus.)

In the right panel you'll find a variety of functions, such as tagging options (for file management), styles (similar to Adobe Lightroom presets; these provide preconfigured edits to selected images), metadata editing, and export options (to convert edited raw files to image files).

The lighttable is used mainly for file management and export; you won't typically perform edits in this area except, perhaps, for batch processing with styles (but I don't recommend this approach).

If you want to edit an individual raw file, you have two options: you can double-click on it, or you can select it and then click on "darkroom" to the top right of window. Either way, you'll be taken to the darkroom.

darktable for Windows: darkroom

The darkroom is where the real magic happens. Here you can take control over the appearance of your final image through a seemingly endless (and, therefore, initially intimidating) choice of tool modules.

At the centre of the screen, you'll see the image you are editing. At the bottom of the screen, you'll see thumbnails of other images, which can be double-clicked for quick editing access. Between the main screen and the film strip of images is a narrow bar with several icons; these include, on the left, quick access to presets and styles, and on the right, over- and under-exposure warning toggles, and soft-proofing and gamut checking toggles (full disclosure: I have only the faintest idea what the latter two toggles are used for).

The left panel of the screen holds a number of drop-down modules. Snapshots allows you take a quick grab of your image at a given point in the editing process, and later compare that snapshot to the edited image as it currently stands. The history module shows all of the edits you have made to the raw file. These edits are stored in an XMP sidecar file--what this means, in simple terms, is that no edits are made to the original file itself; this is why darktable is described as a nondestructive editor. You will probably notice that even if you have opened a file for the very first time, there will be some items listed in the history module; this is because darktable applies certain basic adjustments automatically. Under the history module are a global colour picker module, a tagging module, an image information module, and a mask editor module. The mask editor module allows you to manage masks that you have used to apply local edits to particular areas of your image (versus applying the edits to the entire image).

The right panel of the darktable is where most of your work takes place. At the top of the panel, you'll see the histogram for your image, as well as some basic image information. There are various options for how the histogram is displayed, and if you wish, you can perform some very basic edits on your image by dragging either side of the histogram. Under the histogram are seven icons, linking you to various groups of editing modules. In the above example, you can see the basic group (accessed by clicking the plain circle icon), with the base curve module expanded. At the bottom of the panel you will see an area labeled 'more modules'; here you can control which modules are displayed for easy access, which modules are hidden, and which modules are included in your favourites section.

So that is a very basic overview of darktable, quite possibly using some incorrect terminology (the darktable user manual, for example, uses panels to refer to areas such as the history stack and the mask manager rather than to the different areas of the screen). Interested in learning more? Keep an eye on this site, or delve further into the manual by clicking here.

darktable is nondestructive, free, and open-source, and available for a variety of operating systems (chances are pretty good that yours is one of them). It was designed by photographers, for photographers--and in my experience, the photographers' influence is easily seen in all of its functions. Check it out if you like how it looks!