Gray Balancer is a free, Windows-based program for neutralization gray
color. When gray is made really neutral, the remaining colors are
closer to original. Program generates file with several gray patches.
The file must be printed on a photo printer or via digital lab.
Then, the image is photographed and GrayBalancer is used to remove any
color cast. The color transformation can be either directly used to
correct several images or it can be saved as .AMP file that is used
by Adobe PhotoShop in "curves".
Gray Balancer user interface
consists of a main dialog and several helper windows. The windows can
be freely moved on desktop. Image preview window can be also resized.
The position and size of all windows is saved to configuration file and
reloaded next time GrayBalancer is started.
This group is used to generate files with gray targets.
It is possible to generate two kinds of target: 2*3 and 1*9 patches.
The files must be later printed on a photo printer or exposed via
digital lab. It is important to achieve as good color neutrality as
Therefore, it is better to use only black ink and don't print
the target with color inks.
To minimize reflections, matte paper is recommended.
It is not important to get the exact gray values - the printed
image can be both darker or lighter without any significant
degradation of the result. Only color neutrality is important.
Photograph with target
This part of the main dialog is used to select the file with photo
containing the gray target. It is either possible to directly write
the full path or
to locate the file in browser. Thanks to use of CxImage
library, GrayBalancer can work with all basic
image formats: JPEG, TIFF, BMP, PNG and TGA. The images must be in
TrueColor (24 or 32 bits per pixel). EXIF and color profiles are not
supported. The preview windows support basic operation
like zoom in/out (+/- on numeric keyboard), scrolling (cursor keys),
zoom to fit (End) and Zoom 1:1 (Home).
The program does not know how to find the gray target on a
photograph. Therefore, user must click on the white and black patches
in preview window. First, the type of the target on photograph must
be selected in "Target" group. Then, left mouse click will select
the white patch and right click will select the black one.
After both points are entered, the target is displayed in preview
window. Only the displayed squares are used during computation.
All computations are performed after mouse button is released.
Therefore, it is possible to press the button, move mouse pointer
until all patches are positioned correctly and then finally
release the button.
Gray Balancer can not only neutralize gray color but it cal also
change overall contrast. By default, this feature is turned off.
Usually, when you take a photo of the gray target, the black patch
is not really black (RGB=0) and the white is not 100% white (RGB=255).
Typical range is something like 20..230. When you want to move the
black/white point to another value, just specify the new value.
By specifying bigger range (say 10..240), the overall contrast is
increased. When smaller range is used (like 50..200) the contrast
of the image is decreased.
RGB values from the image at the position of mouse pointer are
displayed here. Two numbers are displayed for each channel. The
first number is the original value, the second number is the value
RGB values from the image must be somehow transformed into gray
level. GrayBalancer supports three different ways how to perform
this task: First, Gray can be computed as average of Red, Green and
Blue. Second, Average with Green taken twice (most of digital cameras
have single Red and Blue and two Green sensors and Green channel is
sensitive to noise). The last possibility is to take directly the Green
channel. In the reality, the differences between all these options are
not big and the default R+2G+B mode will be sufficient
in most cases.
This part of the dialog controls what exactly is displayed. Toggles in
this group have no influence on the result but they may help with
visualization of the whole process.
- show the
squares that are used for computation. This way, it is easy to check if
black and white points were entered correctly and fix any possible
- when the toggle is checked, the image preview show
the final result after gray balancing. Otherwise, the preview always
show the original image. As gray balancing takes some time, it may be
useful to turn this option off during black/white point selection. When
the black/white patches are correctly selected, the option can be again
Curves - show the window actually describing the gray balancing
transformation. The horizontal axis show input values 0..255. The
vertical axis show the output values. Individual channels are displayed
with corresponding color. Measured values are highlighted.
Histogram - show window with histogram of the original or final
image. The horizontal axis show values 0..255 and vertical axis display
frequency of each values. To see histogram of the final image,
push and hold left mouse button in the histogram window. Note that
histogram of the final image is usually not smooth.
Save the current result to disk. To protect the original file,
an appendix "_out" is added at the end of file name. However,
both file name and file type can be freely modified.
Save the transformation to disk. It is possible to save either just the
measured values into a text file or the complete transformation can be
saved into .AMP file and used later in PhotoShop Curves tool.
Apply on images
Perform the gray balancing on a several files. The files can be in
JPEG, TIFF, PNG, BMP or TGA format with 24 or 32 bits per pixel. Old
files are replaced by new versions without any prompt. Warning
: to get good result, all
images must be shot at exactly
The newly created images don't have any EXIF
info or color profile. To preserve existing EXIF info, backup it before
balancing gray value and restore it afterwards. The backup and restore
tasks can be done for example in Zoner
Example of gray balancing
Program GrayBalancer is freeware (free for any commercial and
non-commercial usage). It was tested only with Windows 2000 but
anything better than Windows 98 should be enough to run.
The program does not
need any installation - just copy all the files into a directory
and run gbalancer.exe
Download GrayBalancer 1.21 build 30-Mar-2004: GBalancer121.zip
(c) Libor Šindlar,