Yeah, but the functions I want to teach you are only a small part of Gimp functionality and we're going to approach it with that linearity - no need for me to overwhelm you (and everybody else reading) with a complete Care and Feeding the Gimp.
Here's all you need to be able to do with the Gimp, and why. I'm just going to outline what'll be offered here:
1) Cropping and resizing, so you have only the coin for the viewer to see and your processor to think about. A nice square no larger than the coin is the preferred way to present a coin, and all those excess pixels just unduly burden the computer when you perform later operations. So the very first thing you do with any image in postprocessing is crop to the coin. It speeds the whole rest of the process.
Sizing, on the other hand, is the
last thing you will do with each image, and you'll do that on a case-by-case basis depending on where you're going to use it. There will always be one copy saved (always save as a copy; never alter the original) full size and processed. If you're lucky and getting images still larger than 800 pixels (the ideal minimum for grading-quality images), save a second set at around 800 or 1000 pixels in diameter to offer online. You can even change the "quality" of the final image to make the filesize smaller, and that step has the neat benefit of letting you then use the CCF Optimizer (the one everyone always complains about) to post grading size and quality images here.
2) Sharpening. It is my personal habit to do all sharpening that I plan on ever using with the image as the second step of processing. That way you're acting on the largest-possible image, so any downsizing you do later will only help (downsizing increases apparent sharpness; it's a cool thing). And any alteration you may later make in color or contrast might have its' effects overdone by a later sharpening step.
This is my personal workflow, and I think others might do it differently. Hopefully they'll weigh in and share.
The Gimp has a really nice, really granular Sharpening function. I feel it's a bunch smoother than Photoshop's. It's good enough, in fact, to not need to worry about learning Unsharp Mask to get truly effective sharpening. And you really don't want to play with Unsharp Mask anyway. There lies madness.
So that Sharpening is one of the reasons I'm such a big Gimp fan.
3) Color corrections. Gimp allows you to alter coloration by only affecting one "channel" of color, among six channels. That means removing the slight (or even heavy) yellow cast on your image (for instance) is trivial. This is why you haven't heard me talk about White Balance much; I know we can fix that later if necessary. You can also alter Saturation - "back off" the brightness of color - if need be, because some cameras get a little enthusiastic in their interpretation of color.
It should be mentioned that it is not a sin to do whatever the heck you want to a coin image in postprocessing in order to make the image on your monitor look closer to the coin in your hand.
3) Contrast. Getting contrast right is the goal, the Job One of producing grading-quality coin images. That's why you can pick out the details of the hair above the ear of a Morgan or the sharpness of Lincoln's beard - sufficient contrast lets those small details be seen. Gimp (like most capable postprocessing software) has a nice granular Contrast adjustment. Free contrast? Sign me up. I pretty much automatically increase Contrast by 10% with images intended to be posted online. Some folks' monitors are more washed-out or turned brighter than others, and I don't want them losing out.
4) Saving copies with Quality changes. As mentioned above. Most of the stuff I shoot ends up saved in Original, Processed Full Size, Processed Posting Size Large (about 2000px) and Small (about 1000px). Some photo hosts, and some forums, would really rather you don't throw around 2000-pixel pictures - they're not smart enough to realize that your huge pic is a small file, they just limit you because they see the pixel size even though it's the filesize they want to control.
That's it. There are other beneficial features, but nothing else vital to what you want to do.
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Posted 01/02/2015 2:21 pm
Its kicking my tail so far. 
