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I have RSI problems and have tried 30 different computer keyboards which all caused me pain. Playing piano does not cause me pain. I have played piano for around 20 years without any pain issues. I would like to know if there is a way to capture MIDI from a MIDI keyboard and output keyboard strokes. I know nothing at all about MIDI but I would like some guidance on how to convert this signal into a keystroke.
I haven't done any MIDI programming in years, but your fundamental idea is very sound (no pun).
MIDI is a stream of "events" (or "messages"), two of the most fundamental being "note on" and "note off" which carry with them the note number (0 = C five octaves below middle C, through 127 = G five octaves above the G above middle C, in semi-tones). These events carry a "velocity" number on keyboards that are velocity sensitive ("touch sensitive"), with a force of (you guessed it) between 0 and 127.
Between velocity, chording, and the pedals, I'd think you could come up with quite a good "typing" interface for the piano keyboard. Chording in particular could be a very powerful technique — as I mentioned in the comments, it's why rank-and-file stenographers can use a stenotype machine to keep up with people talking for hours in a row, when even top-flight typists wouldn't be able to for any length of time via normal typewriter-style keyboards. As with machine stenography, you'd need a "dictionary" of the meanings of chords and sequences of chords. (Can you tell I used to work in the software side of machine stenography?)
To do this, the fundamental pieces are:
Receiving MIDI input. Don't try to do this yourself, use a library. Edit: Apparently, the Java Sound API supports MIDI, including receiving events from MIDI controllers. Cool. This page may also be useful.
Converting that data into the keystrokes you want to send, e.g. via the dictionary I mentioned above.
Outputting the keystrokes to the computer.
To be most broadly-compatible with software, you'd have to write this as a keyboard device driver. This is a plug-in to the operating system that serves as a source for keyboard events, talking to the underlying hardware (in your case, the piano keyboard). For Windows and Linux, you're probably going to want to use C for that.
However, since you're just generating keystrokes (not trying to intercept them, which I was trying to do years ago), you may be able to use whatever features the operating system has for sending artificial keystrokes. Windows has an interface for doing that (probably several, the one I'm thinking of is SendInput but I know there's some "journal" interface that does something similar), and I'm sure other operating systems do as well. That may well be sufficient for your purposes — it's where I'd start, because the device driver route is going to be awkward and you'd probably have to use a different language for it than Java. (I'm a big fan of Java, but the interfaces that operating systems use to talk to device drivers tend to be more easily consumed via C and similar.)
Update: More about the "dictionary" of chords to keystrokes:
Basically, the dictionary is a trie (thanks, #Adam) that we search with longest-prefix matching. Details:
In machine stenography, the stenographer writes by pressing multiple keys on the stenotype machine at the same time, then releasing them all. They call this a "stroke" of the keyboard; it's like playing a chord on the piano. Strokes frequently (but not always) correspond to a syllable of spoken language. Like syllables, sometimes one stroke (chord) has meaning all on its own, other times it only has meaning combined with following strokes. (Think "good" vs. "good" followed by "bye"). Although they'll be heavily influenced by the school at which they studied, each stenographer will have their own "dictionary" of what strokes they use to mean what, a dictionary they will continuously hone over the course of their working lives. The dictionary will have entries where the stenographic part ("steno", for short) is one stroke long, or multiple strokes long. Frequently, there will be several entries with the same starting stroke which are differentiated by their length and by the subsequent strokes. For instance (and I won't use real steno here, just placeholders), there may be these entries:
A = alpha
A/B = alphabet
A/B/C = alphabetic
A/C = air conditioning
B = bee
B/C = because
C = sea
D = dog
D/D = Dee Dee
(Those letters aren't meant to be musical notes, just abstract markers.)
Note that A starts multiple entries, and also note that how you translate a C stroke depends on whether you've previously seen an A, a B, or you're starting fresh.
Also note that (although not shown in the very small sample above), there may be multiple ways to "play" the same word or phrase, rather than just one. Stenographers do that to make it easier to flow from a preceding word to the next depending on hand position. There's an obvious analogy to music there, and you could use that to make your typing flow more akin to playing music, in order to both prevent this from negatively affecting your piano playing and to maximize the likelihood of this actually helping with the RSI.
When translating steno into standard text, again we use a "longest-prefix match" search: The translation algorithm starts with the first stroke ever written, and looks for entries starting with that stroke. If there is only one entry, and it's one stroke long, then we can reliably say "that's the entry to use", output the corresponding text, and then start fresh with the next stroke. But more likely, that stroke starts multiple entries of varying lengths. So we look at the next stroke and see if there are entries that start with those two strokes in order; and so on until we get a match.
So with the dictionary above, suppose we saw this sequence:
A C B B C A B C A B D
Here's how we'd translate it:
A is the start of three entries of varying lengths; look at next stroke: C
A/C matches only one entry; output "air conditioning" and start fresh with next stroke: B
B starts two entries; look at next stroke: B
B/B doesn't start anything; take the longest previous match (B) and output that ("bee")
Having output B = "bee", we still have a B stroke in our buffer. It starts two entries, so look at the next stroke: C
B/C matches one entry; output "because" and start fresh with the next stroke: A
A starts three entries; look at the next stroke: B
A/B starts two entries; look at the next stroke: C
A/B/C only matches one entry; output "alphabetic" and start fresh with the next stroke: A
A starts three entries; look at next stroke: B
A/B starts two entries; look at next stroke: D
A/B/D doesn't match anything, so take the longest previous match (A/B) and use it to output "alphabet". That leaves us with D still in the buffer.
D starts two entries, so we would normally look at the next stroke — but we've processed all the strokes, so consider it in isolation. In isolation, it translates as "dog" so output that.
Aspects of the above to note:
You have a buffer of strokes you've read but haven't translated yet.
You always want to match the most strokes against a single entry that you can. A/B should be translated as "alphabet", not "alpha" and "bee".
(Not shown above) You may well have sequences of strokes that you can't translate, because they don't match anything in the dictionary. (Steno people use the noun "untranslate" -- e.g., with our dictionary, the strokes E would be an "untranslate".)
(Not shown above) Some theories of steno allow the same set of strokes to mean more than one thing, based on a broader context. Steno people call these "conflicts". You probably want to disallow them in your project, and in fact when steno used to be translated manually by the stenographer, conflicts were fine because they'd know just by where in the sentence they were what the right choice was, but with the rise of machine translation, conflict-free theories of steno arose specifically to avoid having to go through the resulting translated text and "fix" conflicts.
Translating in real time (which you'd be doing) means that if you receive a partial match, you'll want to hold onto it while waiting for the next chord — but probably only up to a timeout, at which point you'd translate what you have in the buffer as best you can. (Or maybe you don't want a timeout; it's your call.)
Probably best to have a stroke that says "disregard the previous stroke"
Probably best to have a stroke that says "completely clear the buffer without outputting anything"
Consider doing something in hardware that emulates a usb (or ps/2?) keyboard. You will no longer be dependent on a specific OS, or specific OS API. A hardware solution will stand the test of time. Don't be stuck using an old API in Windows 7 when everyone else is running Windows 11! Arduino is pretty easy to learn.
Arduino MIDI hardware is available off of the shelf
Arduinos have been used to emulate keyboard devices
There is a ton of info and help out there for Arduino. It is a hardware hacking platform built for newbies. It will only get bigger now that Google is pushing Arduino.
EDIT: Virtual USB Keyboard software and hardware
It sounds to me like you're looking less for advice on how to build this yourself and more asking what resources are already out there to accomplish what you want. Depending on your OS, there are many ways to accomplish this without having to write your own program from scratch:
MIDI Stroke
Free. For Mac OS X 10.3 and up. This one specifically comes with "the ability to use any MIDI keyboard as a full blown computer keyboard replacement."
Bome's MIDI Translator
Free/Postcardware (it's a bit odd). For Windows 2000 and up, and Mac OS X. It initially appears to be more geared towards AutoHotkey-type usage, but on further looking I think it could do what you want nicely.
Max and aka.keyboard
Free. For Mac OS X. Not exactly a "ready out of the box" solution, but if you are comfortable with basic device configuration, it shouldn't be too bad.
You can access the hardware with source code samples in .NET in MIDI DotNet.
A complete working sample as sourcecode to create MIDI notes data stream is in VB 5/6-Tipp 0521: MIDI-Töne erzeugen (Visual Basic 6.0, somewhere is .NET version too)
A way to simulate keyboard strokes is in VB 5/6-Tipp 0155: Tastaturereignisse simulieren (Visual Basic 6.0, somewhere is .NET version too)
And recognize keystrokes is describedin Tipp-Upload: VB.NET 0266: Globaler KeyHook.
Then, just use a good working matrix for a piano player
On piano and when you're a good player, you can have 10 fingers on the keyboard and if the matrix is usable you can be much more quickly that any computer keyboard user I think. :-)
In that case, if I understand your question right, it should not be a big thing.
I studied piano performance in college and then got into interaction design, programming, and using Vim, so I have actually spent a lot of time prototyping things like this.
You can get this working pretty quick in Linux by using the graphical programming language for multimedia artists, "Pure Data," along with the x11key external by Alex Andre.
On Mac, you can use MidiStroke. I believe a method on Windows involved the MidiOx and AutoHotKey tools. At another time I had a version going using the Java plugin for Max/MSP. I believe Patrice Colet made a windows external for Pure Data that worked as well, but I can't seem to locate it anymore. Also, there's an external for MaxMSP that can do this on Windows. Finally, the non-free but awesome Osculator can do what you want - see the features page.
When I got it working, I never stuck with it, because I couldn't stop tooling with the layout. It was cool just having my monitor on my electric keyboard, though! Good luck.
About MIDI
You stated that you "know nothing at all about MIDI". MIDI technology is fairly straight-forward once you grasp it, but it can be confusing at the outset. One of the resources that has been tremendously helpful for me in understanding the foundations for MIDI (which are certainly necessary if you want to program MIDI interactions), is a book called MIDI for the Technophobe. It's an easy book to read and is very helpful.
Pure Data & Max
In my experience developing interactive multimedia, there are two very similar programs I have encountered that facilitate connecting and mapping signals/inputs from any device.
These are Max for a Mac environment and Pure Data for a PC environment. Both have a plethora of online documentation and YouTube tutorials. The video Max/MSP Tutorial 1 - using your computer keyboard as midikeyboard (ableton style) demonstrates a program built in Max that maps a computer keyboard to a MIDI keyboard's inputs (which is basically the exact opposite of what you are trying to do). You could get your intended results by using the same pattern, but reversing the signals/mappings.
AutoHotKey
AutoHotKey is a free open source utility for Windows that allows you to remap keys and buttons on your devices to macros. It natively supports QWERTY keyboards, joysticks and mouse macros.
However, I was able to find an implementation supporting the specific mapping you are looking for. These two threads explain the process:
MIDI IN support in AutoHotkey , the discussion of the use case. The author was looking for a program that could detect MIDI IN input and translate that to keypresses.
MIDI input library , the solution to the author's problem and the posted code/patch to AutoHotKey which actually implements your intended result.
Basically, it looks like AutoHotKey, along with this user's custom patch, will provide exactly what you need to create a mapping from a MIDI keyboard to a QWERTY keyboard's input signal. All you would have to do is install, configure and define your mappings.
Anything else?
Some of the other answers have given you much more extensive information on MIDI and MIDI programming, in general, but as your post states that doesn't seem to be quite what you are looking for. I would like to help you more if possible, but it would be easier if you could be more specific about the type of information you are looking for. For instance, are you more interested in how to convert a MIDI keyboard's input signals to a QWERTY keyboard's signals, or is your primary interest finding an out of the box solution to your specific problem? What are you looking for that has not yet been addressed?
You could hack your own USB keyboard pretty quickly using a Teenys micro controller.
In fact, they have example code for how to make a USB keyboard.
You could approach this two ways:
Get an old piano and wire up switches directly to the teensy
Add the additional logic to connect to the MIDI port and necessary decoding.
Actually, I worked on this a while ago, trying to capture Rock Band drum inputs into my computer (making a little Java homemade drum emulator) Anyway, I asked a question on here about that, Time delay problem (there is polling code in there, along with what I was attempting to do.). And if I can find my program I can give you the code, it uses a third-party API (JInput).
Good luck either way.
Try Bome's MIDI translator.
It works cross platform, can convert any MIDI input to a keystoke easily, quick to setup and configure, plus it's free for personal use.
There is a tutorial, Quick Tip: MIDI Translation – MIDI to Keystrokes, of how to easily set it up:
Basically, there are infinite possibilities of what you can do, including chording and modifier keys. I use it for my live audio rig to control my DAW using my piano and have never had an issue.
In Java, you can use JMF (Java Media framework) to convert MIDI signals.
Basic of keyboard design is easy to use, that is, the user interface; and place frequently used charcter/symbol handy.
The sample code and API in Java Sound Resources: Examples: Digital Signal Processing (DSP) help to understand how to process the signal.
Some more references:
Processing Audio with Controls
Digital Audio Signal Processing, 2nd Edition
A good library in .NET with full midi support (BASS), go to http://www.un4seen.com.
And for the other part, translating keyboard midi notes to keys and more, I would go for AutoItX, the ActiveX/COM and DLL interface to autoIt. Info and download, go to http://www.autoitscript.com/site/autoit/
No need to write keyboard driver.
There is a program called GlovePIE. You can program it in a simple scripting language, and I believe it supports MIDI. I'm not sure if this fits under the "Java" category, but still, it is a great program. I've used it to control robots using PS3 controllers. It's very powerful.
Many keyboards have a serial port (RS-232) connector to send MIDI signals to the computer. I use a program called Girder to convert serial port communication into keyboard strokes.
Girder has a "mapping" feature that lets you map each key, one by one, to the corresponding keystroke.
This might be the simple solution you're looking for!
Just learn stenography!
It's clear from all the discussion on your part. You don't want to re-invent any wheels, from a technical standpoint. But once you have a connection made (what this question is asking) and up and working, you still have most of the work ahead of you: You have to train your brain. You also have to invent the cleverest, most efficient way to do that - a design issue totally out of the rhealm of computer techies. You or any of us would fall short.
Fortunately, the problem has been solved and honed though centuries of maturing...
Learn stenography!
Yes, this will set you back some jack. But what are hundreds of hours of your own time worth, with at the end, a less favorable result? Besides, the stenography Wikipedia article says, 'it looks more like a piano keyboard'.
Unless, of course, you want to have a sideshow effect going. I would have to admit, I never thought of this possibility, it it would be really entertaining to see somebody bust out a text from a piano keyboard!
You could start with a USB keyboard with touchpad (or a pointing stick would be more ergonomic?), use Plover to translate it (I'm sure it can be configured to let the non-letter keys retain their functionality as they are critical for programming), or, follow the thread Re: Plover keyboard to roll your own USB stenography keyboard, or, buy a stenotype.
Good luck!
Take a look at MAME arcade gaming. They have built hardware devices to allow input from any number of different items. The iPac, for example, converts signals from input devices into USB that the computer can then use to emulate keys. You could use any combination of input devices arranged any way that seems comfortable with no crazy programming logic required--because the software to interpret input is already done and well tested.
I've seen flight simulator cockpit inputs, custom kiosks, and voting systems built in this method.....and the price is right!
To solve this you will need a few things:
A way to capture MIDI data from your keyboard. Depending upon the interface: MIDI interface (classic) or USB MIDI interface (modern) the most likely interface is to a computer as it provides the most options. USB host microcontrollers are not as simple as just using a computer.
A scheme to convert MIDI data into keystrokes. Like one user pointed out, chords are the way to go as the number of keys will not be dependent upon the number of piano keys.
A way to inject a key into the operating system. This will require a low-level driver to be accurate. I have played around with applications that inject keyboard and mouse data into applications in Windows 7, and it can be flaky and depend upon whether an application is currently in focus. This is hardest part of the interface. What may work is to create a HID USB keyboard microcontroller that also has a serial interface.
The serial interface would create a virtual serial port. The software that reads the MIDI data and produces the keystrokes could send a serial message to the virtual serial port. The microcontroller would send a keystroke so it would look like a standard keyboard input. This would allow interfacing both MIDI ports and USB MIDI keyboards.
Hmmm, with this type of interface you could also simulate a mouse and use some piano keys setup for the mouse axis and buttons. The pressure could be used to determine mouse pointer velocity. So you could eliminate the mouse as well. Another benefit of this approach is any type of input device you connect could talk to the virtual serial port to produce keyboard and mouse events. So if you wanted to add other hardware such as drum pedals or a joystick it would be a matter of adjusting the program that talks to the serial interface.
Another take on the above is like some posted above to use an Arduino, but also include USB Host Shield from Sparkfun to handle USB based music keyboards. This allows the Arduino to be programmed as a keyboard or keyboard mouse combo in the boot loader chip and allows the device to act a USB host for the USB based music keyboard. Then you are covered for both types. Although, I still think the virtual serial port method is more flexible and would be easier to program in the long run. The Arduino device will be harder to change than a desktop program or service.
There is another possibility:
Chorded one handed keyboards already exist. I have seen videos on them, but you would have to determine if those hurt your hands or not.
It should be fairly easy using something like the .NET DirectSound interface to hook into an MIDI device. You will need to identify your target MIDI device and then get the code to listen in on the incoming messages (there are articles about doing this via Google).
Since you are using the MIDI in as a keyboard there are basically only two MIDI messages that you need to detect, namely note on and note off. The MIDI message is three data bytes specifying the command, the note and the velocity. The note off is just the note number (sometimes 'bad' MIDI stacks send a note on with zero velocity which you also have to expect).
Once you have the messages translating them the keyboard output should be fairly simple from .NET.
There is plenty of advice in the other answers about the technicalities; I just wanted to give you an idea of the actual MIDI messages. Good luck!
You'll get better and happier results (regardless what operating system and/or DAW program you like to use) by playing any external MIDI keyboard as a controller through your sound card. Then route that into your GB software (or whatever) and tone generate the many sounds they have supplied you that way in real-time.
If your sound card does not support MIDI I/O's (ins / outs /thrus), that's not a problem. You can consider researching and investing in an external MIDI table top converter. Many are equipped to further convert MIDI outs to USB 2.0 (by- passing an existing sound card altogether).
For example: it's pretty tough getting "human like" grace note results via a Z and X change key option using a computer keyboard and pencil tool. When, instead, your own fingers can just play that with a MIDI keyboard from its own physical octave register ranges—immediately!
I realize budgetary constraints may be involved. But, some of these seemingly cheap "Casio" type 5 octave keyboards sold at Radio Shack for under $100.00 U.S. Dollars (*or less) is all you would need (plus, some of their on-board sound patches and sequencer modules sound and handle amazingly well for other things too).
RadioShack MIDI keyboard options.
As for external MIDI converters for existing sound cards, I've run some Google searches for you as follows with Mac platforms specifically in mind:
A lot of this external MIDI conversion information may be cumbersome to you at first, so I've broken down things more as "user friendly" for your considerations & budget:
MIDI sound cards
There's nothing wrong with facilitating virtual keyboards as VST's when using DAW. They have their place.
But, you sound like an accomplished keyboardist. So, why not consider the external MIDI conversion / keyboard options I just mentioned for yourself?
Good luck and I hope this gave you some ideas that can and will work for you!
If you don't want to do any programming yourself but just want the problem solved you can just buy a USB-MIDI-keyboard where you can re-assign any key to send a QWERTY keyboard output signal instead of a MIDI-output, for example M-Audio Axiom Pro
This method will work with any OS and any computer that supports standard USB-keyboards since the MIDI-keyboard will identify itself as a standard QWERTY keyboard.
You can use a simple AutoIt script to both read MIDI events, see MIDI Input.
You'll also need MIDI UDF and simulate key presses.
Reading MIDI events should be easy, but different MIDI controllers (instruments) have different features. Try to find out what your MIDI piano can do first, then see how you can best map those features to simulated QWERTY-keyboard presses.
If you want, you could have something on screen or in the tray to help you see what you are doing (that is, for Shift, Ctrl and Alt simulation).
You might take a look at chorded keyboards. They have the advantage that you don't need to write a driver for them before you can use them, and some are similar to the layout of a piano keyboard.
If you know coding in Java, you could use this way:
First, implement a javax.sound.midi.Receiver with a send(..) method that is mapping the 'Note on' events to keystrokes like you want.
You would need to get the MidiMessage's content with its getMessage method and intepret it in your fashion. The meaning of the message bytes can be found in MIDI Messages.
After receiving a 'note on' or 'note off' for a certain keyboard key, you may map that to a key you like by assigning it a constant of the KeyEvent class, something like C#4 -> KeyEvent.VK_A and so on. This key code can then be used by java.awt.Robot's keyPress and keyRelease methods to actually send the keystroke to the OS and thus to other applications.
I agree with Brian O'Dell's answer - if this were my project, I'd do it in hardware. It has the advantage of being platform and hardware independent - your box replaces the need for a MIDI-USB interface and a PC API.
mbed is a fast-prototyping platform that is very easy to learn, and has multiple advantages over Arduino IMHO (online compiler, 512 KB flash, 96 MHz, C++ language). It has a USB keyboard interface and a USB Midi interface pre-written for you.
The community is very friendly and willing to help, and there are a lot of existing projects using both MIDI and USB hid emulation - search Youtube for "mbed MIDI" or similar.
If you use Linux have a take at Footware.
It should be exactly what you're looking for - if you adjust the MIDI pitches to a keymapping of your liking...
I never thought this could be useful for anyone but me ;o)
Try using a microcontroller-based system, like Arduino.
This wouldn't be too tough.
I'm assuming you're on Windows, not sure about that though. I've written a MIDI sequencer, http://pianocheetah.com, in plain old C++, and it lets you use the piano keyboard to run commands. There isn't any reason you couldn't do the same thing to push keys
into the keyboard input stream.
But come on now. You remember how long it took you to learn
the keyboard in the first place, right?
Are you willing to go through that again?
And are you willing to pollute your blessed keyboard with
a bunch of stupid looking key symbols all over it?
You'll need to use at least 26 alpha, 10 numeric, 11 punctuation,
and at least 12 function keys AND their shifted states.
So that's 60 keys plus shifted states.
That'll burn up a full 5 octaves of keys.
You will be doing piano "hops" =all= the time.
Say goodbye to touch typing.
You may save yourself from RSI, but you've created another
different type of nightmare for yourself.
And good luck getting your boss to buy you a MIDI keyboard at work.
If you've learned to truly play piano, you've learned
how to play stress free. Do that on the QWERTY keyboard.
No tension. Start slow.
Given two seperate computers, how could one ensure that colours are being projected roughly the same on each screen?
IE, one screen might have 50% brightness more than another, so colours appear duller on one screen. One artist on one computer might be seeing the pictures differently to another, it's important they are seeing the same levels.
Is there some sort of callibration technique via software you can do? Any techniques? Or is a hardware solution the only way?
If you are talking about lab-critical calibration (that is, the colours on one monitor need to exactly match the colours on another, and both need to match an external reference as closely as possible) then a hardware colorimeter (with its own appropriate software and test targets) is the only solution. Software solutions can only get you so far.
The technique you described is a common software-only solution, but it's only for setting the gamma curves on a single device. There is no control over the absolute brightness and contrast; you are merely ensuring that solid colours match their dithered equivalents. That's usually done after setting the brightness and contrast so that black is as black as it can be and white is as white as it can be, but you can still distinguish not-quite-black from black and not-quite-white from white. Each monitor, then, will be optimized for its own maximum colour gamut, but it will not necessarily match any other monitor in the shop (even monitors that are the same make and model will show some variation due to manufacturing tolerances and age/use). A hardware colorimeter will (usually) generate a custom colour profile for the device under test as it is at the time of testing, and there is generally and end-to-end solution built into the product (so your scanner, printer, and monitor are all as closely matched as they can be).
You will never get to an absolute end-to-end match in a complete system, but hardware will get you as close as you can get. Software alone can only get you to a local maximum for the device it's calibrating, independent of any other device.
What you need to investigate are color profiles.
Wikipedia has some good articles on this:
https://en.wikipedia.org/wiki/Color_management
https://en.wikipedia.org/wiki/ICC_profile
The basic thing you need is the color profile of the display on which the color was seen. Then, with the color profile of display #2, you can take the original color and convert it into a color that will look as close as possible (depends on what colors the display device can actually represent).
Color profiles are platform independent and many modern frameworks support them directly.
You may be interested in reading about how Apple has dealt with this issue:
Color Programming Topics
https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/DrawColor/DrawColor.html
You'd have to allow or ask the individual users to calibrate their monitors. But there's enough variation across monitors - particularly between models and brands - that trying to implement a "silver bullet" solution is basically impossible.
As #Matt Ball observes calibrating your monitors is what you are trying to do. Here's one way to do it without specialised hardware or software. For 'roughly the same' visual calibration against a reference image is likely to be adequate.
Getting multiple monitors of varying quality/brand/capabilities to render a given image the same way is simply not possible.
IF you have complete control over the monitor, video card, calibration hardware/software, and lighting used then you have a shot. But that's only if you are in complete control of the desktop and the environment.
Assuming you are just accounting for LCDs, they are built different types of panels with a host of different capabilities. Brightness is just one factor (albeit a big one). Another is simply the number of colors they are capable of rendering.
Beyond that, there is the environment that the monitor is in. Even assuming the same brand monitor and calibration points, a person will perceive a different color if an overhead fluorescent is used versus an incandescent placed next to the monitor itself. At one place I was at we had to shut off all the overheads and provide exact lamp placement for the graphic artists. Picky picky. ;)
I assume that you have no control over the hardware used, each user has a different brand and model monitor.
You have also no control over operating system color profiles.
An extravagant solution would be to display a test picture or pattern, and ask your users to take a picture of it using their mobile or webcam.
Download the picture to the computer, and check whether its levels are valid or too out of range.
This will also ensure ambient light at the office is appropiate.
I'm interesting in learning about the different layers of abstraction available for making graphical applications.
I see a lot of terms thrown around: At the highest level of abstraction, I hear about things like C#, .NET, pyglet and pygame. Further down, I hear about DirectX and OpenGL. Then there's DirectDraw, SDL, the Win32 API, and still other multi-platform libraries like WxWidgets.
How can I get a good sense of where one of these layers ends and where the next one begins? What is the "lowest possible level" way of creating a window in Windows, in C? What about C++? (A code sample would be divine.) What about in X11? Are the Windows implementations of OpenGL and DirectX built on top of the Win32 API? Where can I begin to learn about these things?
There's another question on SO where Programming Windows is suggested. What about for Linux? Is there an equivalent such book?
I'm aware that this is very low-level, and that there are many friendlier tools available, but I would like to at least learn the basics of what's going on beneath the surface. As much as I'd like to begin slinging windows and vectors right off the bat, starting with something like pygame is too high-level for me; I really need to make the full conceptual circuit of how you draw stuff on a computer.
I will certainly appreciate suggestions for books and resources, but I think it would be stupendously cool if the answers to this question filled up with lots of different ways to get to "Hello world" with different approaches to graphics programming. C? C++? Using OpenGL? Using DirectX? On Windows XP? On Ubuntu? Maybe I ask for too much.
The lowest level would be the graphics card's video RAM. When the computer first starts, the graphics card is typically set to the 80x25 character legacy mode.
You can write text with a BIOS provided interrupt at this point. You can also change the foreground and background color from a palette of 16 distinctive colors. You can use access ports/registers to change the display mode. At this point you could say, load a different font into the display memory and still use the 80x25 mode (OS installations usually do this) or you can go ahead and enable VGA/SVGA. It's quite complicated, that's what drivers are for.
Once the card's in the 'higher' mode you'd change what's on screen by accessing the memory mapped to the video card. It's stored horizontally pixel by pixel with some 'dirty regions' of pixels that aren't mapped to screen at the end of each line which you have to compensate for. But yeah, you could copy the pixels of an image in memory directly to the screen.
For things like DirectX, OpenGL. rather than write directly to the screen, commands are sent to the graphics card and it updates its screen automatically. Commands like "Hey you, draw this image I've loaded into the VRAM here, here and here" or "Draw these triangles with this transformation matrix..." take a fraction of the time compared to pixel by pixel . The CPU will thank you.
DirectX/OpenGL is a programmer friendly library for sending those commands to the card with all the supporting functions to help you get it done smoothly. A more direct approach would only be unproductive.
SDL is an abstraction layer so without bothering to read up on it I'd guess it would have different ways of working on each system. On one it might use semi-direct screen writing, another Direct3D, etc. Whatever's fastest as long as the code stays cross-platform..able.
The GDI/GDI+ and XWindow system. They're designed specifically to draw windows. Originally they drew using the pixel-by-pixel method (which was good enough because they'd only have to redraw when a button was pressed or a window moved, etc.) but now they use Direct3D/OpenGL for accelerated drawing (and special effects). Optimizations depend on the versions and implementations of these libraries.
So if you want the most power and speed, DirectX/openGL is the way to go. SDL is certainly useful for getting the most from a cross-platform environment and integrates with OpenGL anyway. The windowing system comes last but don't underestimate it. Especially with the stuff Microsoft's coming up with lately.
Michael Abrash's Graphics Programming 'Black Book' is a great place to start. Plus you can download it for free!
If you really want to start at the bottom then drawing a line is the most basic operation. Computer graphics is simply about filling in pixels on a grid (screen), so you need to work out which pixels to fill in to get a line that goes from (x0,y0) to (x1,y1).
Check out Bresenham's algorithm to get a feel for what is involved.
To be a good graphics and image processing programmer doesn't require this low level knowledge, but i do hate to be clueless about the insides of what i'm using. I see two ways to chase this - high-level down, or bottom-level up.
Top-down is a matter of following how the action traces from a high-level graphics operation such as to draw a circle, to the hardware. Get to know OpenGL well. Then the source to Mesa (free!) provides a peek at how OpenGL can be implemented in software. The source to Xorg would be next, first to see how the action goes from API calls through the client side to the X server. Finally you dive into a device driver that interfaces with hardware.
Bottom up: build your own graphics hardware. Think of ways it could connect to a computer - how to handle massive numbers of pixels through a few byte-size registers, how DMA would work. Write a device driver, and try designing a graphics library that might be useful for app programmers.
The bottom-up way is how i learned, years ago when it was a possibility with the slow 8-bit microprocessors. The direct experience with circuitry and hardware-software interfacing gave me a good appreciation of the difficult design decisions - e.g. to paint rectangles using clever hardware, in the device driver, or higher level. None of this is of practical everyday value, but provided a foundation of knowledge to understand newer technology.
see Open GPU Documentation section:
http://developer.amd.com/documentation/guides/Pages/default.aspx
HTH
On MSWindows it is easy: you use what the API provides, whether it is the standard windows programming API or the DirectX-family API's: that's what you use, and they are well documented.
In an X windows environment you use whatever X11-libraries that are provided. If you want to understand the principles behind windowing on X, I suggest that you do this, nevermind that many others tell you not to, it will really help you to understand graphics and windowing under X. You can read the documentation on X-programming (google for it). (After this exercise you would appreciate the higher level libraries!)
Apart from the above, at the absolutely lowest level (excluding chip-level) that you can go is to call the interrupts that switch to the various graphics modes available - there are several - and then write to the screen buffers, but for this you would have to use assembler, anything else would be too slow. Going this way will not be portable at all.
Another post mentions Abrash's Black Book - an excellent resource.
Edit: As for books on programming Linux: it is a community thing, there are many howto's around; also find a forum, join it, and as long as you act civilized you will get all the help you can ever need.
Right off the bat, I'd say "you're asking too much." From what little experience I've had, I would recommend reading some tutorials or getting a book on either directX or OpenGL to start out. To go any lower than that would be pretty complex. Most of the books I've seen in OGL or DX have pretty good introductions that explain what the functions/classes do.
Once you get the hang of one of these, you could always dig in to the libraries to see what exactly they're doing to go lower.
Or, if you really, absolutely MUST learn the LOWEST level... read the book in the above post.
libX11 is the lowest level library for X11. I believe the opengl/directx talk to the driver/hardware directly (or emulate unsupported ops), so they would be the lowest level library.
If you want to start with very low level programming, look for x86 assembly code for VGA and fire up a copy of dosbox or similar.
Vulkan api is an api which gives you very low level access to most if not all features of the gpu, computational and graphical, it works on amd and Nvidia gpus (not all)
you can also use CUDA, but it only works on Nvidia gpus and has access to computational features only, no video output.