Rate checkbox with scanned image in node.js

Question

I want to evaluate whether the check box is checked or not with the scanned image. I found a node module like node-dv and node-fv for this. But when I install this, I got the following error on mac.

../deps/opencv/modules/core/src/arithm1.cpp:444:51: error: constant expression evaluates to 4294967295 which cannot be narrowed to type 'int' [-Wc++11-narrowing] static int CV_DECL_ALIGNED(16) v64f_absmask[] = { 0xffffffff, 0x7fffffff, 0xffffffff, 0x7fffffff }; ^~~~~~~~~~ ../deps/opencv/modules/core/src/arithm1.cpp:444:51: note: insert an explicit cast to silence this issue static int CV_DECL_ALIGNED(16) v64f_absmask[] = { 0xffffffff, 0x7fffffff, 0xffffffff, 0x7fffffff }; ^~~~~~~~~~ static_cast<int>( ) ../deps/opencv/modules/core/src/arithm1.cpp:444:75: error: constant expression evaluates to 4294967295 which cannot be narrowed to type 'int' [-Wc++11-narrowing] static int CV_DECL_ALIGNED(16) v64f_absmask[] = { 0xffffffff, 0x7fffffff, 0xffffffff, 0x7fffffff }; ^~~~~~~~~~ ../deps/opencv/modules/core/src/arithm1.cpp:444:75: note: insert an explicit cast to silence this issue static int CV_DECL_ALIGNED(16) v64f_absmask[] = { 0xffffffff, 0x7fffffff, 0xffffffff, 0x7fffffff }; ^~~~~~~~~~ static_cast<int>( ) 2 errors generated. make: *** [Release/obj.target/libopencv/deps/opencv/modules/core/src/arithm1.o] Error 1 gyp ERR! build error gyp ERR! stack Error: `make` failed with exit code: 2 gyp ERR! stack at ChildProcess.onExit (/Users/entapzian/.nvm/versions/node/v4.3.1/lib/node_modules/npm/node_modules/node-gyp/lib/build.js:270:23) gyp ERR! stack at emitTwo (events.js:87:13) gyp ERR! stack at ChildProcess.emit (events.js:172:7) gyp ERR! stack at Process.ChildProcess._handle.onexit (internal/child_process.js:200:12) 

Is the above dependency the best solution for my problem? If not, offer me a good solution.

Answer 1

Sorry for the delayed reply, I was very busy yesterday and today. Here is an example that captures predefined areas of an image and determines if checkboxes are full or empty. This is only a starting point and can probably be greatly improved, but it should work if the scanned image is of decent quality.

The first step is to obtain image pixels. Then you get areas of the image that contain checkboxes, capturing them according to the pattern. Finally, you evaluate whether the checkbox is checked by comparing the average brightness of this region in the image with the base brightness of the unverified window.

I recommend using the get-pixels Node.js package to get image pixels.

Here is an example that you can probably customize to suit your needs:

 var get_pixels = require('get-pixels'); var image_uri = 'path_to_image'; get_pixels(image_uri, process_image); var pattern_width = 800, // Width of your pattern image pattern_height = 1100; // Height of your pattern image // The pattern image doesn't need to be loaded, you just need to use its dimensions to reference the checkbox regions below // This is only for scaling purposes in the event that the scanned image is of a higher or lower resolution than what you used as a pattern. var checkboxes = [ {x1: 10, y1: 10, x2: 30, y2: 30}, // Top left and bottom right corners of the region containing the checkbox {x1: 10, y1: 60, x2: 30, y2: 80} ]; // You'll need to get these by running this on an unchecked form and logging out the adjusted_average of the regions var baseline_average = ??, // The average brightness of an unchecked region darkness_tolerance = ??; // The offset below which the box is still considered unchecked function process_image(err, pixels) { if (!err) { var regions = get_regions(pixels); var checkbox_states = evaluate_regions(regions); // Whatever you want to do with the determined states }else{ console.log(err); return; } } function get_regions(pixels) { var regions = [], // Array to hold the pixel data from selected regions img_width = pixels.shape[0], // Get the width of the image being processed img_height = pixels.shape[1], // Get the height scale_x = img_width / pattern_width, // Get the width scale difference between pattern and image (for different resolution scans) scale_y = img_height / pattern_height; // Get the height scale difference for (var i = 0; i < checkboxes.length; i++) { var start_x = Math.round(checkboxes[i].x1 * scale_x), start_y = Math.round(checkboxes[i].y1 * scale_y), end_x = Math.round(checkboxes[i].x2 * scale_x), end_y = Math.round(checkboxes[i].y2 * scale_y), region = []; for (var y = start_y; y <= end_y; y++) { for (var x = start_x; y <= end_x; x++) { region.push( pixels.get(x, y, 0), // Red channel pixels.get(x, y, 1), // Green channel pixels.get(x, y, 2), // Blue channel pixels.get(x, y, 3) // Alpha channel ); } } regions.push(region); } return regions; } function evaluate_regions(regions) { var states = []; for (var i = 0; i < regions.length; i++) { var brightest_value = 0, darkest_value = 255, total = 0; for (var j = 0; j < regions[i].length; j+=4) { var brightness = (regions[i][j] + regions[i][j + 1] + regions[i][j + 2]) / 3; // Pixel brightness if (brightness > brightest_value) brightest_value = brightness; if (brightness < darkest_value) darkest_value = brightness; total += brightness; } var adjusted_average = (total / (regions[i].length / 4)) - darkest_value; // Adjust contrast var checked = baseline_average - adjusted_average > darkness_tolerance ? true : false; states.push(checked); } return states; }