I recently took quite a lot of photos with wrong color temperature (white balance) settings. It is easy to correct the color temperature if the photos are in RAW format. However, all my photos were shot in JPEG format and they are not easy to change. Most image editing tools allow you to adjust the color level or saturation, but not color temperature. I found this GIMP script which does let you manipulate the color temperature directly.

The script is called colortemp and it works with GIMP 2.2, 2.4 and 2.6. Here is the site. To install it, just download the script file colortemp.scm and put it in the script directory of your GIMP installation. On Windows, this location is

32 bit:

C:\Program Files\GIMP-2.0\share\gimp\2.0\scripts

64 bit:

C:\Program Files (x86)\GIMP-2.0\share\gimp\2.0\scripts

Once you have it installed. Open up a photo that you want to modify. The information you need to enter is the color temperature of the original file and the target temperature you want to set. There are two ways to specify the original color temperature. If you know the original color temperature, you can use the slider to specify it. Otherwise, you can use the color picker to pick a white spot on your photo and the program would determine the color temperature for you automatically. For some reason, the first option did not work for me, while the second option worked pretty well.

Click on Filters -> Colors -> Convert Color Temperature to bring up the dialog box.

Click on the drop down box and select From foreground color. Click on the toolbox and select the color picker tool. Use the color picker tool to select a white or gray spot on your photo to set it as the foreground color. Now back to the dialog box and use the slider to specify the target temperature or enter it in the box. You can leave Intensity or Saturation unchanged. Click on OK and the script would change the color temperature for you. If you do not like the changes, simply press Ctrl + Z to undo it.

If you do not know what is the correct color temperature to use for the target temperature, you can read this article to get a better idea about the topic.

For those who are unfamiliar with bokeh, it is the blur in the out-of-focus areas of an image. This effect is easily achieved by using a DSLR camera. On a compact camera, it is difficult to have bokeh because of the small lens and sensor.

You could however “simulate” bokeh effect using an image editor. In this tutorial, I am going to show you how to do it using the open source GIMP.

1. Invoke GIMP and open the image you want to edit.
2. Click on the Free Select Tool.
3. Trace your subject with the Free Select Tool.
   
4. Once your subject is selected, click on Select -> Invert to invert the selection. The background is now selected.
5. Click on Filters -> Blur -> Gaussian Blur… to bring up the Gaussian Blur dialog.
   
6. Enter the size of Blur Radius. You have to experiment a bit to figure out the size. In this example, it is a 10MP image, and I used 20.0 px for the Blur Radius. Click on OK to close the dialog.
7. Save the image under a different name so that the original is unaltered.

Here are the sample photos.

BEFORE

AFTER

The thumbnails are a bit small for you to notice the difference. Click on the thumbnails to see the full size images.

I recently got a used Kodak Pro SLR/c camera. It shoots excellent pictures at a low ISO. However, the picture quality degrades greatly at a higher ISO because of noise. One time I accidentally set the ISO to 800, and almost all of the photos were not usable.

There are quite a few Photoshop plug-ins available to tackle the problem. However, Photoshop is very expensive, and, in addition, the plug-ins are not free. This combination is quite out of reach for most of us.

In this tutorial, I am going to show you how to reduce digital photos noise using free tool – GIMP and the wavelet denoise plug-in. Here are the links for these tools:

GIMP

Wavelet denoise plugin (Windows binary of 0.3.1 )

Please refer to the aforementioned links for installation procedures and the location where you should place the plug-in. Once you have GIMP installed with the wavelet denoise plug-in, follow these steps:

1. Invoke GIMP and open up a photo.
2. Click on Filters -> Enhance -> Wavelet denoise … to bring up the Wavelet denoise dialog.
3. There are 3 color modes to choose from. You don’t have to use them all. Just pick one. I like to use CIELAB.
4. After the color mode is selected, adjust the Threshold and Softness for each channel. Make small adjustments, and keep an eye on the preview window. If you set the Threshold to high, you might lose the sharpness of the photo.
   Before
   
   After
   
5. Click on OK to exit out the plug-in and apply the results to the photo.
6. Click on File -> Save As to save the file to a different name so that you still have the original.

Overall, I am very satisfied with the results. The plug-in author mentioned that it is possible to mask the filter effect with selection to further improve the results. That might be something you will want to try if you are well-versed with GIMP.

I have always wanted to learn how to cut out the background of my photo, but I never got a chance. I finally got around to it using GIMP this afternoon. Here is what I figured out.

1. Invoke GIMP and open a photo of your choice.
   
2. Use the Paths Tool to create a path around the subject. When you are about to close the path, press and hold Ctrl key and click on the first point.
   
3. Click on Select -> From Path to select the subject.
4. Click on Select -> Invert to invert the selection. The background is now selected.
5. Click on Edit -> Cut to cut out the background.
   
6. Save the file.

Not too difficult, is it? Just in case you are wondering, the picture shown is a Shuttle K48 I built a while ago.