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Saving and Loading

This sections includes functions for saving and loading different types of images to and from disk.

[res] image.load(filename, [depth, tensortype])

Loads an image located at path filename having depth channels (1 or 3) into a Tensor of type tensortype (float, double or byte). The last two arguments are optional.

The image format is determined from the filename's extension suffix. Supported formats are JPEG, PNG, PPM and PGM.

The returned res Tensor has size nChannel x height x width where nChannel is 1 (greyscale) or 3 (usually RGB or YUV.

Usage:

--To load as byte tensor for rgb imagefile
local img = image.load(imagefile,3,'byte')

--To load as byte tensor for gray imagefile
local img = image.load(imagefile,1,'byte')

[res] image.getSize(filename)

Return the size of an image located at path filename into a LongTensor.

The image format is determined from the filename's extension suffix. Supported formats are JPEG, PNG, PPM and PGM.

The returned res Tensor has size 3 (nChannel, height, width).

image.save(filename, tensor)

Saves Tensor tensor to disk at path filename. The format to which the image is saved is extrapolated from the filename's extension suffix. The tensor should be of size nChannel x height x width. To save with a minimal loss, the tensor values should lie in the range [0, 1] since the tensor is clamped between 0 and 1 before being saved to the disk.

[res] image.decompressJPG(tensor, [depth, tensortype])

Decompresses an image from a ByteTensor in memory having depth channels (1 or 3) into a Tensor of type tensortype (float, double or byte). The last two arguments are optional.

Usage:

local fin = torch.DiskFile(imfile, 'r')
fin:binary()
fin:seekEnd()
local file_size_bytes = fin:position() - 1
fin:seek(1)
local img_binary = torch.ByteTensor(file_size_bytes)
fin:readByte(img_binary:storage())
fin:close()
-- Then when you're ready to decompress the ByteTensor:
im = image.decompressJPG(img_binary)

[res] image.compressJPG(tensor, [quality])

Compresses an image to a ByteTensor in memory. Optional quality is between 1 and 100 and adjusts compression quality.