lcdtest: LCD Monitor Test Pattern Generator


26-JAN-2010: Release 1.18 uses SDL_ttf to render text, rather than SFont, and uses the free LiberationMono-Regular TrueType font. Updated build system to use SCons 1.20, and eliminate use of some deprecated SCons features. Changed license to GPLv3.
26-MAY-2007: Release 1.08 adds a diagonal crosshatch pattern ("x" command).
26-MAY-2007: Release 1.07 has no code changes. SCons-local has been removed, and the documentation is updated to reflect the build requirement of SCons 0.97 or later.
23-MAY-2007: Release 1.06 has a minor change to CFLAGS handling in SConstruct to support building RPM package. RPMs for Fedora Core 6 are now available.
22-MAY-2007: Release 1.05 builds using SCons rather than Make. This should eliminate problems some users had with the dependency analysis.
7-MAY-2007: Release 1.04 uses the SDL Unicode mapping for key events to support non-US keyboard layouts.


lcdtest is a utility to display LCD monitor test patterns. It may be useful for adjusting the pixel clock frequency and phase on LCD monitors when using analog inputs, and for finding pixels that are stuck on or off. lcdtest uses the SDL library, and is known to work on Linux and Windows.

Here are some small samples of a few of the available test patterns:

solid red pattern green crosshatch pattern analog interface pixel timing/phase setup pattern
Solid red Green crosshatch Analog interface pixel timing/phase setup pattern

Command line:


    lcdtest [options]


    --help         get list of command keys
    --list-modes   list available video resolutions
    --window       display in a window rather than full screen
    -x <count>     use a video mode with the specified horizontal resolution
    -y <count>     use a video mode with the specified vertical resolution

Keyboard commands:

Upon startup, lcdtest will fill the screen with solid red. Pressing keys on the keyboard will change the pattern:

Change foreground color:
r red
g green
b blue
w white
k black
Change pattern:
s solid fill
h horizontal lines
v vertical lines
c crosshatch
d dots
a white vertical lines with two pixel pitch
Line position/spacing
arrows move lines in arrow direction
plus increase spacing between lines
minus increase spacing between lines
0..9 select predefined line spacings
/ or ? toggle display of help message
q or escape exit program

The "a" command is specifically intended for use with LCD monitors connected via an analog VGA (vs. DVI). This pattern should work well for the monitor auto-setup feature. Auto-setup may not get the frequency and phase adjusted optimally, in which case this pattern is also useful for manual adjustment.


lcdtest is made available under the terms of the Free Software Foundation's General Public License, Version 3.

lcdtest is written in C and should be fairly portable. The SDL library is required; it is provided with most Linux distrubutions but can be downloaded and compiled separately as needed.

Source code and binaries for Linux and Windows are available for download.

lcdtest development uses the Subversion revision control system. Instructions for access to the Subversion repository for lcdtest are found at, and there is a web interface to browse the repository at

Related web pages

Last updated January 26, 2010

Copyright 2005, 2007, 2010 Eric Smith

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