Author Topic: Photo Tutorial: Downsizing Images in GIMP  (Read 1781 times)

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Offline Dan Lyke

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Photo Tutorial: Downsizing Images in GIMP
« on: February 26, 2007, 02:01 PM »
GIMP is a free and open source image editing program which is available for Windows, Mac, Linux, and a bunch of other operating systems you haven't heard of.

The whole topic of the value of Open Source software is a long thread that's probably not terribly germaine to the Festool Owner's Group, so I'll leave that for another time, but in my household we have far more computers than we have people, one techie and one non-techie, and I use the Mac for work, my sweety and I both use Linux, a popular free and open source operating system, for our regular computer use, and boot Windows (we have two valid XP licenses) when there's absolutely no other choice. Usually that's for running TurboTax around this time of year. So we value programs that run across different platforms and that encourage interoperability in their data formats and work flows (not so much an issue with image editing, but a problem with, say, spreadsheets and word processing...).

At any rate, I'm a big fan of Open Source software, and GIMP is my image editing software of choice on all of these platforms. So, here's a quick intro to how to use it.

Open up your image using GIMP. Depending on how you've installed it this could involve double clicking on your image file, right clicking and choosing "Open with GIMP", starting up GIMP and choosing "File->Open", or any other of the myriad ways. I'll assume that you can do basic navigation and file operations on your computer.

Once you have the image, to resize it, choose the "Image" menu, and then "Scale Image".



This will bring up a dialog box that will allow you to choose the resulting image size. Enter in a value for the "Width", and the "Height" will change to match the aspect ratio (so that you don't get a "funhouse mirror" effect):



Note that there's a little chain to the right of "Width" and "Height". Sometimes you want to fit an image into a specific size. In my case, this camera takes pictures with some weird sort of vertical height, and even if there's just a touch of distortion, I like values divisible by 4 (if you really want to know, I'll ramble on that, but be warned, that can get technical). So I click on the little chain to break it



and then I'm free to enter any value into "Width" or "Height" that I want to, with out it affecting the other.

Click "Scale", and then choose "File" "Save As...", select a file name, and you'll get a little dialog allowing you to choose different compression factors:



JPEG images use "lossy" compression, which means they throw away portions of the detail in the image and hope you don't notice. Most of the time you don't. If you want to fine tune this, you can click the "Show Preview in image window" check box, and manipulate the "Quality" slider until you absolutely can't stand how bad the picture looks.

Poof! Resizing images is that easy.

However, sometimes the right thing to do isn't so much resizing the image as cropping. Maybe you've got identifying details in the background that'd show where you keep that stash of gorgeous Festools, or maybe you just didn't get in tight enough on the parts that matter when you took the picture. In this case, select the rectangle selection tool:



Then select the region of the image that you want to use, go to the Image" menu, choose "Crop Image", and the image is now reduced to the region of interest!



There's plenty of documentation and tutorials over at the GIMP web site to help you through other operations, hopefully this will get you started on the bits you need to put up simple images here.

And remember that holding down the control key and hitting "Z" will undo your goofs, so feel free to experiment! (And one little confusion for the Mac: yes, it's ctrl-Z, because this is running as an "X" app it keeps the original key mappings, which means the native Mac Cmd keys aren't the standard ones. Annoying if you're a Mac only person, great if you use lots of different platforms and computers.)

« Last Edit: June 26, 2007, 02:43 PM by Dan Lyke »
Accomplished computer geek, novice woodworker, road cyclist, in Sonoma county, northern California.

Offline Dan Clark

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Re: Photo Tutorial: Downsizing Images in GIMP
« Reply #1 on: February 26, 2007, 03:06 PM »
Dan,

I took a quick look 'cause I'm at the office.  That's nice work!   I'll look closer when I get home.

I liked your comments about JPEG's lossy compression.  I think I'll copy some of the praseology into the file type overview.  And, I liked your comments about the Mac.  You're now the Official Mac expert!     ;D

Thanks,

Dan.

Offline Dan Lyke

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Re: Photo Tutorial: Downsizing Images in GIMP
« Reply #2 on: February 26, 2007, 03:27 PM »
I liked your comments about JPEG's lossy compression.  I think I'll copy some of the praseology into the file type overview.

I absolutely must force myself to do some more work, but I'll try to find a decent image to save at a couple of different quality settings so that we can show the effects of JPEG quality degredation.

And, I liked your comments about the Mac.  You're now the Official Mac expert!     ;D

Oh dear...  ;)

Alas, I often end up being the official "N" expert where "N" covers a lot of ground. And I use a Mac like it's a Unix machine, not like it's a Mac, so I'm generally only good with Mac stuff in those instances where I have trouble making it Unix-ish. Which gives some of my Mac-head coworkers fits.
Accomplished computer geek, novice woodworker, road cyclist, in Sonoma county, northern California.

Offline Dan Clark

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Re: Photo Tutorial: Downsizing Images in GIMP
« Reply #3 on: February 26, 2007, 03:33 PM »
Aha!  I knew it!  You are now the official Mac AND Unix expert!   ;D

Regards,

Dan.