This post explains how to make your photos look better with GIMP, a free open source application, sometimes called the “poor man’s Photoshop.”

Photos often need corrections to look their best, such as:

  • exposure correction (making the photo lighter or darker),
  • color correction (getting rid of unnatural hues and making whites appear white),
  • sharpening (making the outlines of shapes look sharper, which gives a crisper look to the photo.)

Gimp logo 320pxThis post deals with two color correction tools in GIMP: levels and curves, and secondly, with the sharpening tool.  These three basic tools will cover a lot of your photo adjustment needs.

But first, download GIMP and install it by following the instructions for your computer’s operating system.

Next, double click on the icon of GIMP2 to launch the program.  Don’t be worried if it takes a while for GIMP to open.  (It has to load fonts.)

When GIMP opens you will see three panels.  The center one is the editing window.  This is where your photo will appear when you open it.

Opening a Photo with GIMP

In that center panel, under the File menu, select open and navigate to where the photo is that you want to work on. (It’s handy to put your photos in the Pictures folder.) Highlight the name of the photo you want to open and click on the “open” button.  You may get a caution message that asks whether you want to convert the file (change its color space).  Click “convert”.

Using the Levels Tool in GIMP

Under the Colors menu at the top of the editing window, select “levels”.  A window will open labeled “Adjust Color Levels.”

You will see a graph of the distribution of colors in the photo. This is called a histogram.  On the extreme left this graph shows pixels that are completely black (i.e., have no color at all.)  On the extreme right the graph shows pixels that are completely white (have all colors).  The graph of your photo may show some space on the extreme left or right where there are no pixels, i.e., blank graph space.  The object of the levels tool is to get rid of these blank spaces in the histogram. You do this by sliding the triangle on the left rightward to where the dark pixels begin, and sliding the triangle on the right leftward to where the light pixels begin.  (The video below demonstrates this procedure.)  When you have adjusted both sliders, click the “OK” button at the bottom of the window.  This saves your changes.

If your photo needed a lot of histogram correction, the levels tool will accomplish most of what’s needed. You should see a fairly dramatic positive change in the look of your photo after applying the levels tool.

But, not all your photos will need levels correction.  When you look at the histogram of some of them you will see that there are no empty spaces to the left or right in the histogram.  So, there is no need for the levels tool. Go to the second colors correction tool, the curves tool.  This is for making more subtle corrections.

Using the Curves Tool in GIMP

Again, under the Colors menu at the top of the editing window, select “Curves”.

You will see the histogram again, and a 45 degree line from bottom left to top right. Place your cursor somewhere on that line and hold the left mouse button down, while moving the cursor straight up or straight down.  Notice what happens to the photo when you drag that graph line up or down.  The photo gets lighter or darker.  When you drag, try to follow the vertical lines in the window.  Don’t stray to right or left as you drag because this will distort the hue of the photo.You want to correct just the lightness or darkness, not the hue. (That’s done with another tool.)

You can experiment by dragging the curve line up or down at various places.  The curves tool is for minor adjustments. Don’t drag very far up or down, unless you want to make your photo look unnatural.

Again, when you are finished save your changes by clicking on the “OK” button at the bottom of the window.

Using the Sharpening Tool in GIMP

In the editing window under the Filters menu, hover over “Enhance” and then select “Sharpen”.

A window opens showing a portion of your photo.You can move to a different portion by sliding the scroll bars left and right or up and down. Select a portion of the photo that shows some finer detail so that you can notice the effect which the Sharpness slider produces.  Then move the slider to the right.  At some point you will see a dramatic change, like the lines in the photo are popping off the background.  This is too far!  Back off about half way of the difference you slid and settle for that.  You don’t want to over sharpen. This will make your photo look unnatural. Click the “OK” button when you are finished.

Finally, go to the File menu in the editing window and select “Save” (if you don’t want to change the name of the file), or “Save As” if you do, then rename it.  The final step in either case is to click the “Save” button.

Congratulations! You have just learned how to use three basic photo correction tools in GIMP: levels, curves, and sharpening.  Even your good photos will look a little better if you take the time to correct them with these tools.

The video below demonstrates the instructions in this post.  If you click thelittle square with the four little arrows (bottom right corner of the video frame) you will see the video much larger.  It’s much easier to see the detail that way.

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