setImage.js
1.85 KB
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const bmp = require('bmp-js');
const fileType = require('file-type');
/**
* setImage
*
* @name setImage
* @function set image in tesseract for recognition
* @access public
*/
module.exports = (TessModule, api, image) => {
const buf = Buffer.from(Array.from({ ...image, length: Object.keys(image).length }));
const type = fileType(buf);
let bytesPerPixel = 0;
let data = null;
let pix = null;
let w = 0;
let h = 0;
/*
* Although leptonica should support reading bmp, there is a bug of "compressed BMP files".
* As there is no solution, we need to use bmp-js for now.
* @see https://groups.google.com/forum/#!topic/tesseract-ocr/4mPD9zTxdxE
*/
if (type && type.mime === 'image/bmp') {
const bmpBuf = bmp.decode(buf);
data = TessModule._malloc(bmpBuf.data.length * Uint8Array.BYTES_PER_ELEMENT);
TessModule.HEAPU8.set(bmpBuf.data, data);
w = bmpBuf.width;
h = bmpBuf.height;
bytesPerPixel = 4;
} else {
const ptr = TessModule._malloc(buf.length * Uint8Array.BYTES_PER_ELEMENT);
TessModule.HEAPU8.set(buf, ptr);
pix = TessModule._pixReadMem(ptr, buf.length);
if (TessModule.getValue(pix + (7 * 4), 'i32') === 0) {
/*
* Set a yres default value to prevent warning from tesseract
* See kMinCredibleResolution in tesseract/src/ccstruct/publictypes.h
*/
TessModule.setValue(pix + (7 * 4), 300, 'i32');
}
[w, h] = Array(2).fill(0)
.map((v, idx) => (
TessModule.getValue(pix + (idx * 4), 'i32')
));
}
/*
* As some image format (ex. bmp) is not supported natiely by tesseract,
* sometimes it will not return pix directly, but data and bytesPerPixel
* for another SetImage usage.
*
*/
if (data === null) {
api.SetImage(pix);
} else {
api.SetImage(data, w, h, bytesPerPixel, w * bytesPerPixel);
}
return data === null ? pix : data;
};