Editing in Gimp – Threshold and Color to Alpha Tools
As the title identifies, I’ll be using the image editor GIMP to demonstrate the Threshold and Color to Alpha tools. If you don’t already have a copy, head over to GIMP.org and download one. it’s free which is why I use it 
.
This is what we’re shooting for:
Threshold
The Threshold tool turns your image into a true Black and White. That is Black and White only, no shades of grey. You have to carefully choose the image you want to use this effect upon. If the image has too many colors or limited contrast, it may not work too well. However, if in doubt, open up the image and give the Threshold tool a whirl and see how it turns out, a little experimentation may find a brand new trick!
So, let’s take my original image:
You’ll notice that this image has a lot of conrtast and limited colors. It’s perfect for turning the Threshold tool loose on. Now, you’ll find the Threshold tool under Colors > Threshold…
I’ve selected the Threshold tool and am adjusting the slider to get just the effect I want. I think right about here gives good detail. Let’s go with that.
Now we have a black and white image, perfect for using the Color to Alpha tool (Alpha is a fancy name for transparent).
Color to Alpha tool
You can find Color to Alpha under Color > Color to Alpha… Let’s choose that now. Here’s a shot of the open Color to Alpha tool. I selected white in the “From … to alpha” box. As soon as I did that, all the white in the image disappeared like this:
Now we have an image that is only black, black trees. The rest of the image is transparent. Lets add a layer and move it underneath these black trees. If you look at the Layers, Channels, Paths and so on window (it’s usually on the right side of your screen looking something like this:
Let’s add another layer. I’ve circled in red the new layer button. This will add a transparent layer above the tree image. This new layer need to be placed below the trees so just click on the new layer and pull it below the original one. Voila, now you have a clean slate to lay in the background!
I chose a Hubble space telescope image for this background. I opened the space image and scaled it down to fit my tree image. Copied the space image, click on the trees again, clicked on the transparent layer and pasted the space image into it. That’s it. All that is left is a quick rotate of the whole image. I decided that I wanted it rotated to the left so I choose Image > Transform > Rotate 90 counter clockwise. Be sure and click on the finished image and view a larger size version. Much of the detail is lost with the small sizes.
Now, let’s see what you can do!
GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring.
It has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc.
GIMP is expandable and extensible. It is designed to be augmented with plug-ins and extensions to do just about anything. The advanced scripting interface allows everything from the simplest task to the most complex image manipulation procedures to be easily scripted.
>p>GIMP is written and developed under X11 on UNIX platforms. But basically the same code also runs on MS Windows and Mac OS X.
Read MoreOrton Effect with the GIMP
Last week, I posted about a computer meltdown and a reinstall of software including trying to find the GIMP plugins I was using. After finding them and another cool suite of plugins, a twitter mate of mine @alastair_hm commented that he like the Orton Effect plugin. This plugin is located in the Gimphelp.org suite and is found under Script-Fu -> Sharpness -> Softer -> Orton Effect. I had not used this effect so I quickly applied it to an image. I instantly saw the potential for this effect.
I since discovered that the effect was named for MIchael Orton. He sandwiched slides together. For each image, he would take two shots. One overexposed by two stops and one that was overexposed by one stop. This would produce an image that had an impressionistic sense to it. Nowadays, we don’t really need to use a tripod and take multiple shots. Most image editing programs have settings, plugins, addons and etc that could produce this same effect or it an be produced by adding layers onto an existing image.
In GIMP, the Orton Effect copies the image on two additional layers. In the first it overexposes the image and sharpens it, in the second it applies a gaussian blur.
In this photo I used the Orton Effect then added an alpha mask to the blurred layer to fade out the effect in the center of the flower allowing the sharpness to show through.
This image shows the Orton Effect without using an alpha mask.
If you have a favorite GIMP plugin or effect, please let us all know!
Read MoreGIMP Plugins
I’ve had a computer melt down. My main computer’s power supply turned off the lights and now no one’s home. The laptop had a failing HDD. I replaced the HDD in the laptop but had to leave the big computer with someone else to repair the power supply. After replacing the laptop HDD I’ve had to reinstall all software. I upgraded to the latest Ubuntu 9.10 and installed all my favorite apps. However, I couldn’t remember the name of the suite of scripts/plugins I use on GIMP. I googled furiously to find the plugins I have on the main computer. Eventually I found them – FX-Foundry . If you’ve never used this collection before I’d highly recommend it. Like I said, I was frantic to find them to install on the laptop.
In the process I happened across another collection of plugins from gimphelp.org I experimented tonight with an image I took earlier in the day of an old dead tree.
Here’s the originial image:
Cutout script
Infrared Simulation
and my favorite for this image – Make Wonderful
el hombre cielo grande
I decided that it had been far too long since I had pulled out the ol’ camera and took some shots. I walked around this morning with my daughter and took a few experimentals. While editing them on my favorite editing software, the GIMP, I accidentally choose the Threshold option. This gives a very stark black and white image. I was impressed with how the stripes on the shirt contrasted the other elements in the composition.
I decided to use the threshold edit and layer it with an alpha mask and a circular gradiant. This pulled in color and gave me a great color and texture contrast. If all this sounds like goobledy gook and you wouldn’t know your GIMP from a lame Pimp, then check out the GMIP tutorials located on the site here. The second part of this tutorial explains the threshold tool and how to use it.
Read MoreFinding My Emotive Self
This was a little project inspired once again by Chica’s Photo Projectz site. The challenge was to
“Take a photo you like… and play around with it in your favorite editing program to come up with a heavily filtered look that you feel adds to the image and leaves you with an entirely different (when compared to the original), but enjoyable, result.”
I chose an image I took a while back. It’s an emotive portrait. I started fiddling with my filters and sliders in the GIMP. I ended up using a very heavy dose of the oil painting filter followed by some extreme unsharp masking. I liked the warm rich color and the heavy shadow effect. Hopefully this edit has enhanced my emotive effect.
Read More