Have you ever wanted to make a photo go from color to black and white, as in a gradient loss of color? This tutorial will show you how. I used this awful photo here because the color of it is amazing. At the bottom of the tutorial is one photo you can click on and copy with complete visual instructions.
I did this tutorial with Gimp 2.2.12 but it should be nearly identical in other versions of Gimp as well as in Photoshop.
Start Gimp and open up the image you want to fade. Do any flaw editing and color enhancing now and save the new image. Be sure not to overwrite your original image in case you'll need it in the future. Duplicate the image in the layers box and select the upper layer, leaving the settings at normal and 100.
The upper layer should automatically have an alpha channel. You can check by going to Layer> Transparency> Add Alpha Channel. Since there already is one, it's deselected (grayed out).
Then click on Layer> Mask> Add Layer Mask.
A box will pop up, select Layer's Alpha Channel. Hit Ok.
Your layers dialog box should now look like this. Keep settings at normal and 100. Make sure you are still working on the upper layer.
Pick your gradient tool. Foreground (FG) should be white #ffffff and background (BG) should be black #000000. Opacity should be at 100 and mode normal. Reverse checked or unchecked is up to you. I'll cover that in a second. Click the Gradient box and make sure FG to BG (RGB) is selected. To dismiss, click off in the menu box anywhere. I also have my setting at Linear, other settings I'll cover at the bottom of this tutorial.
Click and drag your gradient "brush" across your image as in the example below. You can also go corner to corner for a different effect (the blue dots on the big image at bottom of this tut).
Look in your layers dialog box, it should look like the one below. Where the gradient is white, the image will be in color, where it's black it will desaturate (black and white). If this is not what you want, hit undo, return to your gradient settings and check or uncheck the reverse box and reapply the gradient on the top layer.
Your image is still in color, this is okay. Go to the layers dialog box and select the bottom layer. In the image window select Layer> Colors> Desaturate. Now your image should show the gradient fade.
Flatten image and save. Be sure to rename your image so you don't overwrite your original.
The photo below has two techniques added, this tutorial and the tut I posted just before on enhancing fall photos. Instead of using linear in my gradient settings I used radial, but you can get a similar effect with bilinear. Placement takes a lot of trial and errors. Remember where you start and stop your drag by using your photo as your guide. For instance, I had to use the right edge of the tracks where it goes from land to trestle and drag half way into the woods to the right. It's odd that the white part of the gradient ended up being to the left, but that's how it works, thus having to play with it. You might want to save as a psd or an xcf file before playing so you can go back if you need to.
Another thing to take note is in case your image keeps a small portion colored that doesn't look right, in my case the trees had excessive blue around the tree limbs in the sky, so I went to my layer mask layer and brushed on black in those places and it disappeared.
When I got my color how I wanted it, I flattened my image, then created a new layer, set to overlay mode and bucket filled with my favorite dark brown tint. I moved the opacity until I liked how it looked. Using dark brown did darken my image, it also warmed it up.
The whole tutorial in a single image with pink guide dots is below. Click on the image to get a larger version of it and save picture.