image-compressor
v2.0.3
Published
Frontend javascript module for resizing and compressing images
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Image-Compressor
Frontend javascript module for resizing and compressing images. No backend libraries required.
Version 2.0 released!
Now available as simple import { ImageCompressor } from 'image-compressor';
===============================IMPORTANT==============================
If you want to use it within ES5 JS project under the window
object, you should access it by window.ImageCompressor.ImageCompressor
. Now ImageCompressor is module, so that strange access sequence appeared.
However within ES6 JS project after first import
of the module, ImageCompressor
will be available at window.ImageCompressor
=====================================================================
Image compressor uses canvas in the background for resizing operations. Result image has no dimensional distortions, original image is being compressed with the original aspect ratio.
Original image is centered in the result image. Free space can appear aside of result image due to possible different aspect ratios of original and compressed images.
Such free space is filled with the #FFFFFF
color for image/jpeg
mime type. For image/png
free space aside result image filled transparently.
Demo
Image compressor uses step-down algorithm for scaling down images. That means an image gets compressed for some discrete steps. Within each step image gets compressed by a half(original size : width
, height
, size after first step is width / 2
, height / 2
). Such stepping allows limited interpolation on compressed image and gives more similar to original image result
INSTALLATION
npm install image-compressor
USAGE
Javascript
import { ImageCompressor } from 'image-compressor';
const imageCompressor = new ImageCompressor;
const compressorSettings = {
toWidth : 100,
toHeight : 100,
mimeType : 'image/png',
mode : 'strict',
quality : 0.6,
grayScale : true,
sepia : true,
threshold : 127,
vReverse : true,
hReverse : true,
speed : 'low'
};
...
imageCompressor.run(imageSrc, compressorSettings, proceedCompressedImage);
function proceedCompressedImage (compressedSrc) {
// ...
}
INTERFACE
Image compressor has one useful method: run(imageSrc, compressorSettings, proceedCompressedImage)
imageSrc
: Source of the image to compress/resize. Enabled dataURL or image src url. Be careful with CORS restrictions!
compressorSettings
: Object with the compression settings. Enabled fields :
compressorSettings.mode
: Values strict
, stretch
. Strict mode disables dimensional distortions, stretch mode stretches or squeezes original image to fit result sizes
compressorSettings.toWidth
: Width in pixels of the result (compressed/stretched) image, default : 100
compressorSettings.toHeight
: Height in pixels of the result (compressed/stretched) image, default : 100
compressorSettings.mimeType
: Mime type of the result (compressed/stretched) image, allowed values image/png
, image/jpeg
, default : "image/png"
compressorSettings.quality
: Quality of the result (compressed/stretched) image, allowed values 0-1
with step 0.1
. So 0.5
or 0.8
- correct values , 0.35
or 2
- incorrect values, default : 1
compressorSettings.grayScale
: If you need to apply grayscale filter to pixels of the compressed image, just set this parameter to true. Default : false
compressorSettings.sepia
: If you need to apply sepia filter to pixels of the compressed image, just set this parameter to true. Default : false
compressorSettings.threshold
: Pixel intensity edge to set black and white. Pixels that has intensity larger then number specified in this setting will be converted to white color, if smaller - pixel become black Default : false
compressorSettings.vReverse
: Applies vertical reverse to the result image Default : false
compressorSettings.hReverse
: Applies horizontal reverse to the result image Default : false
compressorSettings.speed
: Compression speed. Allowed values "low"
, "high"
. In the case of the "low"
value quality lossless algorithm is being applied(slower, many steps of compression), "high"
value compresses an image just in one step(faster but with the large delta between original and compressed sizes result image has poor quality). Default : "low"
Width and Height NOTE
If toWidth
or toHeight
did not specified, compressor will use original aspect ratio of an image and will combine it with available toWidth
or toHeight
So for example if an original image size will be 2000x1000 and specified toWidth : 500
result toHeight
will be calculated as 500 * 1000 / 2000
At least one of two above settings must be set to make compressor working correctly
Filters NOTE
You can apply only one filter from available(grayscale, sepia, threshold) to the compressed image. If selected both of them at a time, compressor will use only grayscale
filter
Reversing NOTE
Vertical and horizontal reverses can be applied together. If selected both of them, result image will be reversed diagonally.