picha

picha

picha (swahili): photo

I couldn't find a library or libraries to encode/decode jpeg and png images and also allow raw access to the pixel data - so I wrote one.

Usage

var fs = require('fs');
var picha = require('picha');

var image = picha.decodeSync(fs.readFileSync("test.jpeg"));
var resized = picha.resizeSync(image, { width: 100, height: 100 });
var cropped = resized.subView(20, 20, 60, 60);
var compressed = picha.encodePngSync(cropped);
fs.writeFileSync('tested.png', compressed);

API

Image

new picha.Image(opt)

Construct a new image object from the options opt

• opt.width: width of the image in pixels
• opt.height: height of the image in pixels
• opt.pixel: pixel format (rgb, rgba, grey, greya)
• opt.stride: row stride in bytes - defaults to 4 byte aligned rows
• opt.data: buffer of data

If the data buffer isn't provided an appropriate buffer will be allocated.

Image.subView(x, y, w, h)

Return a new image that is a rectangulare view into this image defined by the supplied pixel coordinates.

Image.copy(targetImage)

Copy the pixels from this image to the target Image. The pixel format must match. If the sizes don't match then overlapping or missing pixels are discarded.

Image.pixelSize()

The size, in bytes, of this images pixel format.

Image.row(y)

Return a slice of buffer for a row of the image.

Image.equalPixels(o)

Return true if this image and another image 'o' are pixel for pixel equal.

Image.avgChannelDiff(o)

Return the average channel by channel difference between this and another image 'o'.

Image codec

picha.stat(buf)

Decode the image header and grab the image vitals. Only yhe first handful of bytes of the image data is required. The function returns null or

{
    width: the width of the image
    height: the height of the image
    pixel: pixel format
    mimetype: one of "image/jpeg" or "image/png"
}

picha.decode(buf, cb)

Decodes the supplied image data on a libuv thread and calls cb with (err, image).

picha.decodeSync(buf)

Decodes the supplied image data on the v8 thread and returns the image.

picha.encodePng(image, cb)

Encode the supplied image into png format on a libuv thread. The cb receives (err, buffer).

picha.encodeJpeg(image, opt, cb)

Encode the supplied image into jpeg format on a libuv thread. The cb receives (err, buffer). The optional opt object may specify { quality: 85 }.

picha.statPng(buf)

picha.statJpeg(buf)

Decode the header of the respective image formats and returns null or an object containing the width, height and pixel format.

picha.decodePng(buf, cb)

picha.decodeJpeg(buf, cb)

Decode the respective image format data on a libuv thread and call cb with (err, image).

picha.decodePngSync(buf)

picha.decodeJpegSync(buf)

Decode the respective image format data on the v8 thread and return the image.

Image manipulation

picha.resize(image, opt, cb)

Resize the image with the provided options. The computation is performed on a libuv thread and cb receives (err, image).

• opt.width: the width to resize
• opt.height: the height to resize
• opt.filter: optional resize filter - cubic (default), lanczos, catmulrom, mitchel, box, or triangle.
• opt.filterScale: optional scale to apply to the filter (0.70)

picha.resizeSync(image, opt)

Resize an image on the v8 thread. The resize image is returned.

picha.colorConvert(image, opt, cb)

Convert the color format of the image. The computation is on the a libuv thread and cb receives (err, image).

• opt.pixel: the pixel format to convert to (rgb, rgba, grey, greya)
• opt.redWeight: optional weight of the red channel for rgb->grey conversion (0.299)
• opt.greenWeight: optional weight of the green channel for rgb->grey conversion (0.587)
• opt.blueWeight: optional weight of the blue channel for rgb->grey conversion (0.114)

picha.colorConvertSync(image, opt)

Convert the color format of the image. The computation is on the v8 thread and the resulting image is returned.

License

MIT