80 lines
4.1 KiB
Markdown
80 lines
4.1 KiB
Markdown
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# UTIF.js
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A small, fast and advanced TIFF / EXIF (+ DNG and other TIFF-ish files) decoder and encoder. It is the main TIFF library for [Photopea image editor](https://www.photopea.com). Try to open your TIFF file with Photopea to see, if UTIF.js can parse it.
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* Supports Black & White, Grayscale, RGB and Paletted images
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* Supports Fax 3 and Fax 4 (CCITT), JPEG, LZW, PackBits and other compressions (1,3,4,5,6,7,8,32773,32809)
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* E.g. [this 8 MPix image](//www.photopea.com/api/img/G4.TIF) with Fax 4 compression is just 56 kB ( [Open in Photopea](https://www.photopea.com?p=%7B%22files%22:%5B%22//www.photopea.com/api/img/G4.TIF%22%5D%7D) )
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## Installation
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Download and include the `UTIF.js` file in your code. If you're in NodeJS or otherwise using NPM, run:
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```sh
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npm install utif
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```
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#### `UTIF.decode(buffer)`
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* `buffer`: ArrayBuffer containing TIFF or EXIF data
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* returns an array of "IFDs" (image file directories). Each IFD is an object, keys are "tXYZ" (XYZ is a TIFF tag number), values are values of these tags. You can get the the dimension (and other properties, "metadata") of the image without decompressing pixel data.
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#### `UTIF.decodeImages(buffer, ifds)`
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* `buffer`: ArrayBuffer containing TIFF or EXIF data
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* `ifds`: the output of UTIF.decode()
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* loops through each IFD. If there is an image inside it, it is decoded and three new properties are added to the IFD:
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* * `width`: the width of the image
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* * `height`: the height of the image
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* * `data`: decompressed pixel data of the image
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TIFF files may have various number of channels and various color depth. The interpretation of `data` depends on many tags (see the [TIFF 6 specification](http://www.npes.org/pdf/TIFF-v6.pdf)). The following function converts any TIFF image into a 8-bit RGBA image.
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#### `UTIF.toRGBA8(ifd)`
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* `ifd`: image file directory (element of "ifds" returned by UTIF.decode(), processed by UTIF.decodeImages())
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* returns Uint8Array of the image in RGBA format, 8 bits per channel (ready to use in context2d.putImageData() etc.)
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### Example
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```javascript
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function imgLoaded(e) {
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var ifds = UTIF.decode(e.target.response);
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UTIF.decodeImages(e.target.response, ifds)
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var rgba = UTIF.toRGBA8(ifds[0]); // Uint8Array with RGBA pixels
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console.log(ifds[0].width, ifds[0].height, ifds[0]);
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}
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var xhr = new XMLHttpRequest();
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xhr.open("GET", "my_image.tif");
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xhr.responseType = "arraybuffer";
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xhr.onload = imgLoaded; xhr.send();
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```
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## Use TIFF images in HTML
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If you are not a programmer, you can use TIFF images directly inside the `<img>` element of HTML. Then, it is enough to call `UTIF.replaceIMG()` once at some point.
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#### `UTIF.replaceIMG()`
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```html
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<body onload="UTIF.replaceIMG()">
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...
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<img src="image.tif" /> <img src="dog.tif" /> ...
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```
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And UTIF.js will do the rest. Internally, an Image elements will be replaced by a Canvas elements. The attributes "id", "class" and "style" will be copied from the original Image to the new Canvas. Use CSS to style such images.
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## Encoding TIFF images
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You should not save images into TIFF format in the 21st century. Save them as PNG instead (e.g. using [UPNG.js](https://github.com/photopea/UPNG.js)). If you still want to use TIFF format for some reason, here it is.
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#### `UTIF.encodeImage(rgba, w, h, metadata)`
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* `rgba`: ArrayBuffer containing RGBA pixel data
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* `w`: image width
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* `h`: image height
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* `metadata` [optional]: IFD object (see below)
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* returns ArrayBuffer of the binary TIFF file. No compression right now.
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#### `UTIF.encode(ifds)`
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* `ifds`: array of IFDs (image file directories). An IFD is a JS object with properties "tXYZ" (where XYZ are TIFF tags)
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* returns ArrayBuffer of binary data. You can use it to encode EXIF data.
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## Dependencies
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TIFF format sometimes uses Inflate algorithm for compression (but it is quite rare). Right now, UTIF.js calls [Pako.js](https://github.com/nodeca/pako) for the Inflate method.
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TIFF format sometimes uses JPEG compression (but it is quite rare). Right now, UTIF.js calls "JpegDecoder" constructor, which comes from [pdf.js](https://github.com/mozilla/pdf.js). You can find it "separated" from pdf.js in libraries such as jpg.js.
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