Examples 3 libvips libvips examples A few example Python programs using libvips This page shows a few libvips examples using Python. They will work with small syntax changes in any language with a libvips binding. The libvips test suite is written in Python and exercises every operation in the API. It’s also a useful source of examples. #!/usr/bin/python3 import sys import pyvips left = 10 top = 10 width = 64 height = 64 image = pyvips.Image.new_from_file(sys.argv[1]) roi = image.crop(left, top, width, height) print('average:', roi.avg()) You can use pyvips.Image.new_from_memory() to make a vips image from an area of memory. The memory array needs to be laid out band-interleaved, as a set of scanlines, with no padding between lines. #!/usr/bin/python3 import sys import time import pyvips from PIL import Image import numpy as np if len(sys.argv) != 3: print(f'usage: {sys.argv[0]} input-filename output-filename') sys.exit(-1) # map vips formats to np dtypes format_to_dtype = { 'uchar': np.uint8, 'char': np.int8, 'ushort': np.uint16, 'short': np.int16, 'uint': np.uint32, 'int': np.int32, 'float': np.float32, 'double': np.float64, 'complex': np.complex64, 'dpcomplex': np.complex128, } # map np dtypes to vips dtype_to_format = { 'uint8': 'uchar', 'int8': 'char', 'uint16': 'ushort', 'int16': 'short', 'uint32': 'uint', 'int32': 'int', 'float32': 'float', 'float64': 'double', 'complex64': 'complex', 'complex128': 'dpcomplex', } # load with PIL start_pillow = time.time() pillow_img = np.asarray(Image.open(sys.argv[1])) print('Pillow Time:', time.time()-start_pillow) print('original shape', pillow_img.shape) # load with vips to a memory array start_vips = time.time() img = pyvips.Image.new_from_file(sys.argv[1], access='sequential') mem_img = img.write_to_memory() # then make a numpy array from that buffer object np_3d = np.ndarray(buffer=mem_img, dtype=format_to_dtype[img.format], shape=[img.height, img.width, img.bands]) print('Vips Time:', time.time()-start_vips) print('final shape', np_3d.shape) # verify we have the same result print('Sum of the Differences:', np.sum(np_3d-pillow_img)) # make a vips image from the numpy array height, width, bands = np_3d.shape linear = np_3d.reshape(width * height * bands) vi = pyvips.Image.new_from_memory(linear.data, width, height, bands, dtype_to_format[str(np_3d.dtype)]) # and write back to disc for checking vi.write_to_file(sys.argv[2]) This makes a 100,000 x 100,000 black image, then inserts all the images you pass on the command-line into it at random positions. libvips is able to run this program in sequential mode: it’ll open all the input images at the same time, and stream pixels from them as it needs them to generate the output. To test it, first make a large 1-bit image. This command will take the green channel and write as a 1-bit fax image. wtc.jpg is a test 10,000 x 10,000 jpeg: $ vips extract_band wtc.jpg x.tif[squash,compression=ccittfax4,strip] 1 Now make 1,000 copies of that image in a subdirectory: $ mkdir test $ for i in {1..1000}; do cp x.tif test/$i.tif; done And run this Python program on them: $ time python try255.py x.tif[squash,compression=ccittfax4,strip,bigtiff] test/* real 1m59.924s user 4m5.388s sys 0m8.936s It completes in just under two minutes on this laptop, and needs about 7gb of RAM to run. It would need about the same amount of memory for a full-colour RGB image, I was just keen to keep disc usage down. If you wanted to handle transparency, or if you wanted mixed CMYK and RGB images, you’d need to do some more work to convert them all into the same colourspace before inserting them. #!/usr/bin/python3 #file try255.py import sys import random import pyvips # this makes a 8-bit, mono image of 100,000 x 100,000 pixels, each pixel zero im = pyvips.Image.black(100000, 100000) for filename in sys.argv[2:]: tile = pyvips.Image.new_from_file(filename, access='sequential') im = im.insert(tile, random.randint(0, im.width - tile.width), random.randint(0, im.height - tile.height)) im.write_to_file(sys.argv[1])