Preparing photos for the web means knowing where the pitfalls are, and a big one is the fact that monitors pixelate, and crunched photos lose their sharpness. You've got to put the details back in when you crunch a photo. The sharpening tools in the GIMP can and should be your friend, but know the working limits of the tool's capabilities. To get to the tool, from the image menu bar select: Filters>Enhance>Sharpen. Select your strength from the slider or the spin box or direct entry. From practice I use the following values as baseline. First sharpening (before reducing) = 29~39. Adjust to tolerance. After the first reduction (1/2 original size) 19~9. After the final reduction, 09~0 for final effect. Once again, adjust to taste, and watch for over-sharpening. It really does look nasty.
Fetch the tool!
Apply the tool!
Eeeeeew! Way over done! Hit the undo and try again!
Ah! Much better. In fact, just about right.
This tool can actually help save a marginally soft shot, but it isn't going to fix a complete failure to focus. The caveats to sharpening are, too much sharpening is worse than not sharp enough. Those nasty white halos around small items and well defined edges, and hard white spots here and there are a sure sign of trying to make the GIMP fix a focus problem.
is! Sometimes sharpness ruins a mood, too. Pulling your wife/girlfriend/significant-other's tiny little facial wrinkles into stark focus is a sure fire way to spend the next two weeks wondering how long it will take the bruises to heal ... whilst sleeping on the couch.
Know what to sharpen
... and what to blur. Much of the time, an overall photo sharpening isn't the best way to handle a shot. If you have a nice crisp subject, and the background is nicely blurred, a whole shot sharpening isn't going to help much. All it's going to do is add a nasty grain to the background. GIMP to the rescue! Use the Blur / Sharpen tool in the left tool box and a FUZZY brush (sized to suit) to selectively sharpen only what you really want clear.
Sharpen in stages.
A little sharpening goes a long way. Whether doing an overall or a selective sharpening, do a little bit at a time and in relatively low strengths. (A handy way to handle this is to duplicate your working layer and get comfy with the undo stack.) Once you get your new layer all tricked out, try reducing its opacity (increase transparency) until it looks natural. (You'll need to add an alpha channel to your working layer. Right click the layer and select, "Add Alpha channel.") Don't worry about flattening the image for the final crunch. That will happen automagically when we do the final merge and save.
A quick (and completely biased) word here about the Unsharp Mask tool. Yeah. It's there, and some people actually use it, but it's the photographic equivalent of using a ball peen hammer on an ingrown toenail. It just ain't pretty, and when you're done .. you probably won't like the results.
White balance in post production:
Fixing FUBARS. If you forgot to white balance your camera (by selecting or shooting something white in the shooting arena before your capture session begins) you can usually fix that fast and dirty by going to the menu. Colors>Auto>White Balance. Most of the time this works, but sometimes it seems like the GIMP is on a controlled substance, and gives some truly silly results. In which case, it's time to hit the undo, and settle into some serious work on the levels.
Now to the meat of the matter. Resize in stages, and never more than half of the starting value in the pixel box. Depending on your camera and its settings, your originals are going to be huge. Way too big to post on-line. Select: Image>Scale Image. This gives you the dialogue box.
Fetching the dialogue box.
A word to the wise here. Remember that everywhere you are going to be displaying these images -- thinks in RGB, and pixels. If you want to be synced up with your tools and your goals, you need to think in these terms yourself.
The Scale Image Dialogue.
Settings here should be as follows: Leave the ratio chain
linked. This eliminates having to double enter info. Width
is more of an issue in web work than depth, so focus your adjustments on this.
Leave this chain linked too, or things will get really ugly, really fast. Most cameras save jpegs at 72 dpi. If you're in Linux, your monitor and vid card are most likely set to 90~98 dpi, with a default of 96. Most everybody else is set there too, so try not to drop under that value. During the adjustment process, I usually alter the resolution settings to 400. Personal choice. Have it your way. Experiment with file sizes and resolutions until you hit on your own nirvana, just remember the lower you go, the worse it looks.
As I mentioned above, sharpen between each reduction stage, but in steadily reducing strengths. Also check your colors again to make sure you aren't crunching into ugly. You'll soon get a feel for what works for you.
Reduce this value each time.
Percentages in Jpegs:
Overly compressed jpegs are as ugly as home made sin. Shoot for your highest quality value which still gives you a reasonably decent file size. You really don't lose much fidelity between 100~85% quality, but anything under 75~50 starts to get ugly ... fast. A good rule of thumb is to shoot for under 120K per photo. Sometimes you can get up to 300, but anything beyond that will get you summarily deleted from any dial-up user's Christmas Card List. Once you've got your photo crunched, right click the layers box and, "merge visible layers." Then go to the File menu, select Save as, and park the thing where you want it to stage for upload.
Here's where you get to make those jpeg quality decisions. There is a preview function here, and I strongly suggest you use it.
Bingo! Crunched, cleaned, sharpened, saved and ready to go.
One final thought.
Can you really trust your own eyes?
The GIMP gives us a stunningly powerful tool to manipulate images. That's both a good thing ... and a bad thing. As illustrated below, just because you've seen it on the web with your own two eyes ... doesn't mean that's what really was.
After. .................. <..