A Full-Featured Open-Source Framework for Image Processing (2024)

Start Here

What you wouldn't give to sit down with Aunt May again, some sunny Sunday morning, and talk about — oh, maybe nothing at all. Talk about nothing at all while the kitchen fills with the warm smell of baking cookies. The kitchen of that quaint, old Victorian gingerbread, now long ago gone.

Well. You've got G'MIC at The Prompt.

And you've got a visual goal: Fix Aunt May's old photograph.

Now — here's the problem: you lack a vocabulary to connect your visual goals to G'MIC commands.

You have no idea what to do. So you throw a Hail Mary! pass:

Imgcreator-AI — zmo.ai

Hey, presto! Stuff happens! A bunch of text. And Aunt May!

Except — you can't seem to do much with it. Mouse over: get read outs. Left or middle mouse buttons: drag. Right: zooms.

What else? C,E,H. Re-positioners. Z. Zooms. G. Makes grids appear. Sometimes.

OK. But this is presentation stuff. What about fixing stuff?

–§§§–

So. Here's the first bit: G'MIC doesn't do Windows, Icons, and Mouse Pointers (WIMP). At least, not much. It mostly does Old School Shell. Like Uncle Ken Olsen hunched over the VT-100, back in the days of DEC.

Not keen on shells? Oh. My. Then you have a bit of a learning curve. But — let's say you can get past that.

Some pipeline following the "gmic" command

Here's the next bit: What you write after gmic is a pipeline. Pipelines are ordered command sequences which operate on image lists. Some people call image lists stacks.

No gmic-qt documentation here

And a third bit: If — instead — you're looking for how sliders or buttons work in the gmic-qt plug-in — the G'MIC inside of paint programs — Sorry. That's Not Here. Nada. Zilch. But! if you want to write such things, you are on the right page. Here, we weigh up the G'MIC command line interpreter and the pipelines you write for that go inside gmic-qt plug-ins too. Get pipelines down and it's just writing the user interface, a kind of a big, fancy comment preceding your pipeline in some command file.

Does any of that pique your interest? Then Start Here.

You write pipelines with the interpreter. Pipelines operate on image lists. Put some pins in that. Pipelines and image lists live at the very core of G'MIC. The Intro Cheat takes a deeper dive, but you've written a pipeline already. You got Aunt May on the stack. She got there because you entered the input command.

Wait — What? Never typed input, you say??!

Ah. That's because G'MIC throws its own Hail Mary passes. Should it encounter an incomplete pipeline — such as the one you wrote — it sticks an implied input command in front of what it guesses to be an image argument. Ditto with output. If G'MIC can't find anything that looks like an output command, it punts, appending a display command to the end of the pipeline.

Hail Mary passes don't always work. These did. You wrote a pipeline: -inputauntmay_oldphoto.png-display, and stumbled onto your first success.

But. You don't want to — just — stumble onto successes. Success only when stars align — Pffft! You want turn-key successes. Successes so common that — you don't even think about them anymore.

Commands, selections and arguments shall a pipeline make

Now. Lets pull the pins. Commands. Image selections. Arguments. Substitution variables. $-expressions. These are what a pipeline makes. A run-down:

There are exceptions. In certain contexts, what look like images selections are selecting things other than images — but that gets ahead of the game. gmichelp <some command> catalogs any such peculiarity.

Mainly, G'MIC commands do image processing. In official distributions, there are a little over nine hundred of them. More than a thousand counting community contributions.

At present you know about two: input and display. It's a start.

Here are two more: output and normalize.

That's enough for a riff. Let's fix up Aunt May — at least a little bit — by re-pegging the illumination range. That is, normalizing it. Type this pipeline at a shell prompt:

Aunt May, normalized from zero to two hundred, fifty-five.

See Also

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Now the old girl has a little more punch. And color! Though still a mess. Yet — progress. A little victory.

Take a look at the text dump. That's the G'MIC shell log: it consists of lines beginning with [gmic] (Official Messages), or sometimes <gmic> (internal minutiae ). It's straightforward: Input. Process (normalize). Output. Typical lines of action. Of course, choosing lines of action may be a bit sketchy for you at the moment. You still know (almost) next to nothing. But the steps forward are plain.

You need to increase your G'MIC vocabulary.

And, as you increase your G'MIC vocabulary, the ways to reach visual goals becomes clearer. So here's the plan:

I want to run the — you know! — the — the — whatchamacallit command. The apply something command. You know. That command.

As you increase your G'MIC vocabulary, you will reach a point where you will have some grasp of maybe a few dozen commands, but many — if not most — are rattling around your head in some half-remembered way. You want to use color_adjust — or is it adjust_color? — command. Or something to do with blur.

G'MIC's help command routinely has to sort out such things, and that command has an internal piece which builds directories from fragments. You can use it too:

Here, following the "print" piece, is the fragment: "apply." G'MIC takes that fragment and gathers together all the command line interpreter ("cli") definitions which has the supplied fragment somewhere in the collected commands' names — that's the "parse_cli" part. It then prints out that list — that's the "print" part. With that list now in front of you, you might recall that it was some apply_curve command which you read about somewhere in some tutorial about programmatically adjusting arguments. So reminded, you can now get specific help:

And while you know (as of yet) only a few commands, you may as well start — right now! — defining your own: say, an easier-to-use version of parse_cli.

Start by creating a file in your home folder (or directory) called:

This file contains your own personal extensions to the G'MIC language. G'MIC reads it every time you use the gmic command and adds whatever custom definitions it finds within. Let your first definition be this (write it inside of your .gmic or user.gmic file):

Apart from observing that this definition is a kind of a template for a new, custom whatis command, we're not going to take you off into the weeds with descriptions of how all the parts and pieces operate. (for that, go to A First Custom Command ). Just save the file in your home directory and — later — when you want to know what kind of blur commands are around, type:

and then get further help on any one of them, say:

An Empyreal Journey

Of course, it's more than vocabulary. It's also grammar, of having G'MIC's whole structure at your beck and call. Sucessions of riffs and finger exercises carry you forward until, one day, an enthralling sense of alchemy overtakes you. You'll grasp the whole from its parts, and never again will you size up an image without having a collateral assay of G'MIC commands rush into your head — it becomes just a part of everyday perception.

In any case, you are now a digital artist. Seek inspiration from the world around you. Look at textures, surfaces, The G'MIC Gallery, clothing fabric, Funny Oneliners, fields of grass. Tree bark. Concrete Textures.

Can you write pipelines that render (maybe somewhat faux) versions of these? Yes you can. At first, keep it simple. Can you make a ramp? Seems probable. How about a diffusion tensor field? Uh. That last one may be a bit of a reach. But keep calm and carry on. With each step toward the more complicated cases, futher riffs and finger exercises suggest themselves. Scrounge around the tutorials. Post questions at Discuss Pixls: G'MIC or gamble a day away on writing one-liners. Always set challenges for yourself. Here are a few to get started:

How to stamp ampersands all over the place Or any other shape. Turn the trick with a small binary image (an ampersand!) and a large, mostly black image, but with scattered pulses — non-zero pixels. The convolution of a pulse and a shape reproduces the shape — on the first pass. What happens with more passes?	XORing the Addressing The exclusive OR (XOR) operator reports False on identical inputs and True on differing inputs. What if we set the value of every pixel in a 128×128 image with the XOR of its coordinates? Can we animate it??
How to animate as if in a dream? Anything that G'MIC can apply to a single image can apply to a sequence. Here: based on a slightly differing warp of an image, one after another, applied in not quite identical ways, to each channel, the lot changing over time. See the tvfritz script in the discuss.pixls.us G'MIC section.	How to make a network of roads? Bandpass salt-and-pepper noise for a smooth-varying pattern that tiles vertically and horizontally. Off-center thresholding — something other than 50-50 — so that either white or black regions connect and the other forms islands. Morphologically thin on the island color so that islands expand to their limits. Blur-and-threshold to finish up. Roadways among the hills, perhaps, or biological cells.

Tutorial Land

If all else fails, read the manuals.

Updated: February 04, 2024 17:30 UTC Commit: ceda63b2867a