Table of Contents

Name

ssocr - optical recognition of seven segment displays

Synopsis

ssocr [OPTION]... [COMMAND]... IMAGE

Description

ssocr reads an image file containing the picture of a seven segment display, recognizes the displayed digits and prints them to standard output. All image formats known by imlib2 are supported. Use - as file name to read the image from standard input. ssocr provides several image manipulation algorithms to enhance noisy images.

Options

-h, --help

Write a help message to standard output. The default settings are shown as well.

-V, --version

Write version information to standard output.

-v, --verbose

Print information about program execution to standard error.

-t, --threshold THRESHOLD

Specify a percentage value as luminance threshold to differentiate between black and white. This threshold is adjusted to the luminance values occurring in the image, unless option --absolute-threshold is used. The default threshold is 50.

-a, --absolute-threshold

Do not adjust the threshold to the luminance values occuring in the image. Consider this option when using the dynamic_threshold command.

-T, --iter-threshold

Use an iterative method (one-dimensional k-means clustering) to determine the threshold. The starting value can be specified with the --threshold option.

-n, --number-pixels NUMBER

Set the number of foreground pixels that have to be found in a scanline to recognize a segment. Can be used to ignore some noise in the picture. See the web page of ssocr(1) for a description of the algorithm.

-i, --ignore-pixels NUMBER

Set the number of foreground pixels that are ignored when deciding if a column consists only of background or foreground pixels. Can be used to ignore some noise in the picture. See the web page of ssocr(1) for a description of the algorithm.

-d, --number-digits NUMBER

Specifies the number of digits shown in the image. Default value is 6. Use -1 to automatically detect the number of digits.

-r, --one-ratio RATIO

Set the height/width ratio threshold to recognize a digit as a one. RATIO takes integers only. See the web page of ssocr(1) for a description of the algorithm.

-m, --minus-ratio RATIO

Set the width/height ratio to recognize a minus sign. This uses the same idea as recognizing the digit one.

-o, --output-image FILE

Write the processed image to FILE. Use - to write to standard output. Unless this option is used no image is written to disk. If a standard filename extension is used it is interpreted as the image format to use. Can be useful together with the --process-only option.

-O, --output-format FORMAT

Specify the image format to use with --output-image. This format must be recognized by imlib2. Standard filename extensions are used to describe the format. Overwrites the image file format automatically determined via the filename. If no format is specified via this option or the filename, png is used.

-p, --process-only

Use ssocr(1) as an image manipulation program. No image recognition is performed. Should be used together with the -B --output-image option.

-D, --debug-image[=FILE]

Write a debug image showing the results of thresholding, segmentation and character recognition to disk. The image is written to the file testbild.png unless a filename FILE is given.

-P, --debug-output

Print information helpful for debugging to standard error.

-f, --foreground COLOR

Specify the foreground color (either black or white). This automatically sets the background color as well. Default is black.

-b, --background COLOR

Specify the background color (either black or white). This automatically sets the foreground color as well. Default is white.

-I, --print-info

Prints image dimensions and range of used luminance values to standard error.

-g, --adjust-gray

Interpret the values T1 and T2 given to the command gray_stretch as percentages instead of absolut luminance values.

-l, --luminance KEYWORD

Choose the type of luminace computation. Using help as KEYWORD prints the list of implemented luminance keywords with a short description of the used formula. The default of Rec709 should work well in most cases.

Commands

dilation

Filter image using dilation algorithm. Any pixel with at least one neighbour pixel set in the source image will be set in the filtered image.

erosion

Filter image using erosion algorithm. Any pixel with every neighbour pixel set in the source image will be set in the filtered image.

closing [N]

Filter image using closing algorithm, i.e. erosion and then dilation. If a number N > 1 is specified, N times dilation and then N times erosion is executed.

opening [N]

Filter image using opening algorithm, i.e. dilation and then erosion. If a number N > 1 is specified, N times dilation and then N times erosion is executed.

remove_isolated

Remove any foreground pixels without neighbouring foreground pixels.

make_mono

Convert the image to monochrome using thresholding. The threshold can be specified with option --threshold and is adjusted to the used luminance interval of the image unless option --absolute-threshold is used.

grayscale

Transform image to gray values using luminance. The formula to compute luminance can be specified using option --luminance.

invert

Set every foreground pixel to background color and vice versa.

gray_stretch T1 T2

Transform image so that the luminance interval [ T1,T2 ] is projected to [ 0,255 ] with any value below T1 set to 0 and any value above T2 set to 255.

dynamic_threshold W H

Convert the image to monochrome using dynamic thresholding a.k.a local adaptive thresholding. A window of width W and height H around the current pixel is used to determine the (local) thresholding value. Consider using the --absolute-threshold option together with a manually adjusted --threshold for predictable results.

rgb_threshold

Convert the image to monochrome using simple thresholding for every color channel. This is the same as --luminance=minimum make_mono. You should use --luminance=minimum and make_mono or dynamic_threshold instead.

r_threshold

Convert the image to monochrome using simple thresholding. Only the red color channel is used. This is the same as --luminance=red make_mono. You should use --luminance red and make_mono or dynamic_threshold instead.

g_threshold

Convert the image to monochrome using simple thresholding. Only the green color channel is used. This is the same as --luminance=green make_mono. You should use --luminance green and make_mono or dynamic_threshold instead.

b_threshold

Convert the image to monochrome using simple thresholding. Only the blue color channel is used. This is the same as --luminance=blue make_mono. You should use --luminance blue and make_mono or dynamic_threshold instead.

white_border [WIDTH]

The border of the image is set to the foreground color. This border is one pixel wide unless a WIDTH > 1 is specified.

shear OFFSET

Shear the image OFFSET pixels to the right. The OFFSET is used at the bottom. Image dimensions do not change, pixels in background color are used for pixels that are outside the image and shifted inside. Pixels shifted out of the image are dropped. Many seven segment displays use slightly skewed digits, this command can be used to compensate this.

rotate THETA

Rotate the image THETA degrees clockwise around the center of the image. Image dimensions do not change, pixels rotated out of the image area are dropped, pixels from outside the image rotated into the new image are set to the background color.

mirror { horiz | vert }

Mirror the image horizontally or vertically.

crop X Y W H

Use only the subpicture with upper left corner ( X,Y ), width W and height H.

set_pixels_filter MASK

Set every pixel in the filtered image that has at least MASK neighbour pixels set in the source image.

keep_pixels_filter MASK

Keep only those foreground pixels in the filtered image that have at least MASK neighbour pixels set in the source image (not counting the checked pixel itself).

Luminance Keywords

Exit Status

Environment

TMP can be used to specify a different directory for temporary files than /tmp.

Bugs

Imlib2 (and therefore ssocr(1)) does not work well with Netpbm(1) images.

Author

ssocr was written by Erik Auerswald <auerswal@unix-ag.uni-kl.de>.

See Also

netpbm(1), ImageMagick(1),

http://www.unix-ag.uni-kl.de/~auerswal/ssocr/


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