How To Fix An Underexposed Digital Photo…


I thought it would be fun to show you how I fixed some of my pictures that were underexposed (too dark). Obviously, it would be best to take the picture at the right exposure from the start, but sometimes that isn’t so easy.

While I was in Vegas, I didn’t have my tripod. After I’d opened up the aperture to f/5.6 and set the ISO to 400 or 800 and had slowed the shutter to 1/4 or 1/8 of a second I was then in dangerous territory, where I risked noise from too much ISO or blur from not being able to hold the camera still during a longer shutter speed. Post production to the rescue!

In the past, I’ve dorked around with using curves or levels to try to lighten up my photos. But what I really wanted was a way to just expose my photo one more stop. I searched the internet and came across this tutorial for Photoshop.

Even though I use Photoshop in lab for class, at home I use GIMP. So, I decided to write up my own tutorial, translating this method into GIMP. You’d be surprised how similar they are.

Here’s my original photo of the spiral escalator. As you can see from the histogram, my shadows are not blown out (bumping up against the left side) so that tells me that I can lighten this and still have some detail in the shadows.

Fix an underexposed photo

To fix an underexposed photo in GIMP, click over to the layers tab (circled in red)…

Next click on the create a duplicate layer button at the bottom (circled in red), notice that a new background copy is created (circled in red)…

Now for the fun part… change the mode from normal to screen (circled in red)
[side note: for overexposed (too light) photos change mode to multiply]…

Did you see the photo suddenly get lighter? But also note that the histogram didn’t change, we’ll talk about that in just a bit.

At this point, I suggest saving the new photo. You can continue to play with it, but I like to save (under a new name) between big changes.

Does it need to be lightened more? Just click on the create a duplicate layer button again. It automatically puts the new layer it in screen mode…

The photo is even lighter. But how do you know when you’ve lightened it enough?

According to my instructor, if your monitor isn’t calibrated you can get a false since of proper exposure. Perhaps your monitor is set really bright (or really dark). Unfortunately, our eyes can’t really tell if the photo is in proper exposure if the monitor isn’t giving us the correct information. But we can use other information to tell us if our photo is correctly exposed.

One such tool is the histogram. If the graph bumps up against either the left (too dark) or the right (too light) side of the histogram, it means that it is blown out in that area. You can do this check on the camera itself to see if you need to take the picture again, by the way.

Ok, so let’s look at the photos I’ve manipulated, and play a little Goldilocks. This is why I save throughout the manipulating process. Open up your saved manipulated photos in GIMP and let’s take a look.

Here’s the original again… note the histogram, there’s a small bump on the right indicating it’s too light in some part of the picture. I can see that it’s a bit overexposed on the column in the right hand side of the photo, but it’s not something that is easily fixed. But the rest of the histogram indicates that this photo is too dark, the majority of the graph is on the left. Luckily, though, it is not bumped up against the left, so it’s not blown out in the shadows. Too dark…

Now let’s look at the first lightened photo, notice that the histogram has moved slightly to the right and has gotten a bit more shallow. Looks good (just right?)…

But just to make sure, let’s look at the photo that was lightened twice. The histogram is really up against the right side, and the graph is really shallow. Too light…

In my opinion, the middle photo is the best of the three. Not perfect, since it does have that slightly blown out part of the column, but that is not as obvious as it is in the too light and too dark photos.

Hope that helps you correct your photos. Keep in mind that even if you use a program different from GIMP, like Photoshop, the method is very similar.

Until next time…
~nic

Advertisements

One thought on “How To Fix An Underexposed Digital Photo…

  1. Pingback: Hummingbirds… « The Auspicious Squirrel

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s