Examples

Examples

These examples are in https://github.com/jcupitt/ruby-vips/tree/master/example

Thumbnail an image

ruby-vips has a thumbnail operator that can make a high-quality image thumbnail efficiently. It has three forms: thumbnail from a file source; thumbnail from an image held as a string; and thumbnail from another image, that perhaps you've already processed.

#!/usr/bin/env ruby# batch-process a lot of files## this should run in constant memory -- if it doesn't, something has brokenrequire'vips'# benchmark thumbnail via a memory bufferdefvia_memory(filename,thumbnail_width)data=IO.binread(filename)thumb=Vips::Image.thumbnail_bufferdata,thumbnail_width,crop: 'centre'thumb.write_to_buffer'.jpg'end# benchmark thumbnail via filesdefvia_files(filename,thumbnail_width)thumb=Vips::Image.thumbnailfilename,thumbnail_width,crop: 'centre'thumb.write_to_buffer'.jpg'endARGV.eachdo |filename|
puts"processing #{filename} ..."thumb=via_memory(filename,500)# thumb = via_files(filename, 500)end

Annotate an image

This example renders some text on to an image.

The ruby-vips text operator makes a one band uchar image with 0 for background and 255 for text, rather like an alpha channel.

To render text on to an image, you make the text image, then expand it to match the size of the image you are rendering to, then use the text mask with ifthenelse to pick between pixels from the image and a constant. ruby-vips uses small arrays to represent pixel values, so [255, 0, 0] is red.

#!/usr/bin/env rubyrequire'vips'im=Vips::Image.new_from_fileARGV[0],access: :sequentialleft_text=Vips::Image.text"left corner",dpi: 300left=left_text.embed50,50,im.width,150right_text=Vips::Image.text"right corner",dpi: 300right=right_text.embedim.width - right_text.width - 50,50,im.width,150footer=(left | right).ifthenelse(0,[255,0,0],blend: true)im=im.insertfooter,0,im.height,expand: trueim.write_to_fileARGV[1]

Daltonize

Implementation of the daltonize algorithm for adjusting images to aid legibility for colour-blind people.

#!/usr/bin/ruby# daltonize an image with ruby-vips# based on# http://scien.stanford.edu/pages/labsite/2005/psych221/projects/05/ofidaner/colorblindness_project.htm# see# http://libvips.blogspot.co.uk/2013/05/daltonize-in-ruby-vips-carrierwave-and.html# for a discussion of this coderequire'vips'#Vips.set_debug true# matrices to convert D65 XYZ to and from bradford cone spacexyz_to_brad=[[0.8951,0.2664, -0.1614],[-0.7502,1.7135,0.0367],[0.0389, -0.0685,1.0296]]brad_to_xyz=[[0.987, -0.147,0.16],[0.432,0.5184,0.0493],[-0.0085,0.04,0.968]]im=Vips::Image.new_from_fileARGV[0]# remove any alpha channel before processingalpha=nilifim.bands == 4alpha=im[3]im=im.extract_band0,:n=>3endbegin# import to XYZ with lcms# if there's no profile there, we'll fall back to the thing belowxyz=im.icc_import:embedded=>true,:pcs=>:xyzrescueVips::Error# nope .. use the built-in converter insteadxyz=im.colourspace:xyzendbrad=xyz.recombxyz_to_brad# through the Deuteranope matrix# we need rows to sum to 1 in Bradford space --- the matrix in the original# Python code sums to 1.742deut=brad.recomb[[1,0,0],[0.7,0,0.3],[0,0,1]]xyz=deut.recombbrad_to_xyz# .. and back to sRGB rgb=xyz.colourspace:srgb# so this is the colour error err=im - rgb# add the error back to other channels to make a compensated imageim=im + err.recomb([[0,0,0],[0.7,1,0],[0.7,0,1]])# reattach any alpha we saved aboveifalphaim=im.bandjoin(alpha)endim.write_to_fileARGV[1]

Creating image of a specific colour

Create a new image with specific pixel values ( from Stackoverflow ):

value=[50,100,150]# RBG Valuespixel=(Vips::Image.black(1,1) + value).cast(:uint)image=pixel.embed0,0,1200,630,extend: :copy

Create a composite image

Create a composite image from two other images:

background=Vips::Image.new_from_file'background.jpg'photo=Vips::Image.new_from_file('600.jpeg'))out=back.compositephoto,"over",x: 100,y: 100out.jpegsave('out.jpg')