Dark Photos
One problem you can run into is a picture that is too dark. It could happen because you took a photo at night, or in an area with low light levels, such as a dense forest. Can it be fixed? Yes, to some degree. But bear in mind you cannot create information that was not captured in the first place. I have a few photos I took in Heidelberg, Germany that had this problem on a sunny day because the sky was so bright that the camera adjusted to the sky, thus making the city scene too dark. So how do I handle this problem?
- First, open the photo in GIMP.
- Go to the Colors Menu–>Levels. This will open a pop-up window to Adjust Color Levels. This becomes a trial-and-error process, but you may be amazed at what you can do with just a few simple tweaks.
- By default, when you open the Adjust Color Levels pop-up, the setting for Channel will be Value. Leave it there for the moment. This means you will be adjusting all three color channels equally, which means it is just the overall darkness or brightness.
- Underneath that is the Input Levels setting. There is a histogram, and underneath it is a long box with triangles. These are sliders, and there are three of them, though one may be half hidden if it is all the way to one side. They are for Black, Gray, and White.
- Note that there is a check-box on the lower right of the pop-up for Split View. This will split the screen down the middle so you can see the original side-by-side with your modified version. I recommend using this. You will see it on other pop-ups we use as well.
- Start with the middle slider, and move it to the left. You should see the picture start to brighten. Depending on the original photo, this may be all you need to do. As I said, it is trial-and-error, and what matters most is if you like the picture you are getting. But you can try to modify a bit more with other two sliders.
- Then if you wish you can go back to the Value setting, and select each of the Primary colors of Red, Green, and Blue, and adjust them as well.Click OK if you like what you have which will close the Adjust Color Levels pop-up.
- Next go to the Colors menu and select Exposure. This will open another pop-up window.
- In this pop-up window you can adjust the Exposure and the Black Level. Make any adjustments you need to make here. Remember to use Split View.
- When you like what you have click OK, closing the pop-up.
- For more tweaking you can go to the Color menu and select Color Temperature. This term is something that comes from physics and is somewhat technical and rather counter-intuitive to me. We tend to think of Reds and Oranges as “warm” colors and Blues and Whites as “cool” colors, but in Color Temperature it is just the opposite. But you don’t really need to get into all of this if you just want to think of this as another possible tweak to your photo.
- Adjust the sliders for Original Temperature and Intended Temperature until you like the result, then click OK to accept this and close the pop-up window.
- One last adjustment can be made by going to the Color Menu and selecting Curves.
- This pop-up has a graph with a diagonal line running up from left to right, but you can click on the line and drag it to create a smooth curve. Usually you want to create something like the letter S by dragging the right side up a little and the left side down a little. but I would again use the Split View to make sure to not overdo it.
- Export the photo. I append “-fixed” to the original file name, and keep the original file when I do this.
This may sound very daunting, but it doesn’t have to be. If you are a graphic designer or some other type of visual artist you should probably take the time to master all of these tools as part of your craft, but for a hobbyist who takes holiday snapshots, like me, maybe only one or two of these tweaks will do what is needed. For one of my photos from Heidelberg, all I really needed to do was make the first adjustment in Adjust Color Levels and I was fine with the result. The only thing you should care about is if you have photos you like.
If you want a little more information check out this video from Digitivity: https://www.youtube.com/watch?v=G8OJJbhNWGs
Color Adjustments
My wife has some pictures that are 50 years old that haven’t aged well. For example, a number of them have a strong green tint that probably is due to degradation of the Magenta dye in the film, leaving just the Cyan and Yellow, which of course combine to form Green. GIMP can of course fix this to some degree, and this is a couple of ways to go about it.
Color Balance
- Open your photo in GIMP
- Go to the Color Menu and select Color Balance. This will open a pop-up window.
- In this window you can adjust the colors for three different ranges, your Shadows, Midtones, and Highlights. You will see the biggest effect with Midtones in most pictures, but do work all three. Remember to use Split View.
- The sliders underneath let you adjust individual color ranges, and work by sliding toward one color and away from the complement. So if you slide toward Cyan, you will add more Cyan to the picture you will get less Red, more Magenta means less Green, and more Yellow means less Blue.
- This again is trial-and-error. You won;t get a perfect result right away, but get it is close as you can, then click OK to accept the changes and close the pop-up window.
For relatively minor adjustments this is a fairly easy approach, but not a flexible and powerful as the next method.
Adjust Color Levels
- Go to the Color Menu and select Adjust Color Levels.
- This becomes a lot like the previous adjustment for dark photos, only now the color channels become even more important. So use the sliders to adjust the Red, Green, and Blue levels as needed.
- Also make sure to check the Output Levels to fine-tune the result.
- When you get the best result, Click OK to close the pop-up window and accept the picture.
- Export the finished product.
If you have serious degradation the result is not going to be perfect. GIMP can only work with the information it has. But I was able to get significantly better results on those old photos.
About Histograms and Levels
A Histogram is a graph statisticians use to look at a frequency distribution, which means how many observations fall into a certain range or category. In GIMP, the Histograms are telling you about the number of pixels with a certain value. So at the far left you have pure Black, or pure Red, or pure Green, or pure Blue, depending on that selection. And on the right is pure White, pure Red, etc. In the Adjust Color Levels pop-up, when you leave it on Value it is looking at Black and White. So a very dark picture will have a high curve to the left because there are lots of dark pixels, and a low curve to the right because there are fewer light pixels. The three triangle sliders help adjust the balance. If you pull the left-most triangle to the right, you are telling GIMP to treat every pixel up to and including that value as pure Black, which will darken the picture. If you pull the right-most triangle to the left, you are telling GIMP to treat every pixel from that value upwards as if it was pure White. The middle triangle is for setting your mid-point. When you move it to the left, you are shrinking the area below the midpoint, reducing the amount of darkness, so the image lightens. And of course moving it to the right increases the area below the midpoint, making the image darker.
Something similar happens when you move to the color channels, only instead of the black-and-white balance you are working with the amount of the color. But it is a little different. For example, if you are on the Red channel and you move the left-most triangle to the right you are telling GIMP that all pixels to the left of the triangle should now be Cyan, the complement to Red. This will make the picture more Blue. And if you move the right-most triangle to the left it tells GIMP to make all pixels to the right of the triangle Red, resulting in a Redder picture. This is all done by mathematics, of course, since the essence of digital photography is to encode the level of colors as numbers. GIMP is an 8-bit program, so the numbers range from 0 to 255, and you can see that under the sliders where there are numbers. These show the position of the far left and far right sliders, and you can fine tune them using the up and down arrows next the number. Do you need to know this to use this tool? Perhaps not, but it may help you to use it more effectively.
For a good video try this from Davies Media Design: https://www.youtube.com/watch?v=jbU8FqTI-A4
And with that I conclude my GIMP series, at least for now. I did what I set out to do.