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pythonmatplotlibrastertiff

Saving a tiff raster file with matplotlib.image.imsave and matplotlib.pyplot.savefig give outputs of different sizes

I have a numpy array of dimension (10980x10980).

When I save it using matplotlib.image.imsave('file.tiff',data), viridis pseudo colorscheme is automatically applied to the plot. I did this, and obtained a tiff file of 480 MB.

If I save the same figure using matplotlib.pyplot,

plt.imshow(data)
plt.colorbar()
plt.savefig('file.tiff')

I obtain a file of around 1.5 MB.

The tiff info of both the files are:

  1. Using matplotlib.image.imsave:
TIFF Directory at offset 0x8 (8)
  Image Width: 10980 Image Length: 10980
  Resolution: 100, 100 pixels/inch
  Bits/Sample: 8
  Compression Scheme: None
  Photometric Interpretation: RGB color
  Extra Samples: 1<unassoc-alpha>
  Samples/Pixel: 4
  Rows/Strip: 10980
  Planar Configuration: single image plane
  1. Using pyplot.savefig:
TIFF Directory at offset 0x8 (8)
  Image Width: 640 Image Length: 480
  Resolution: 100, 100 pixels/inch
  Bits/Sample: 8
  Compression Scheme: None
  Photometric Interpretation: RGB color
  Extra Samples: 1<unassoc-alpha>
  Samples/Pixel: 4
  Rows/Strip: 480
  Planar Configuration: single image plane

We can see that plt.savefig has reduced the dimensions to 640x480. Why was it? And how to change this?

Solution

  • You are doing two different operations.

    matplotlib.image.imsave('file.tiff',data) saves the data contained in 'data' into a tiff (essentially an array that can be viewed as an image.

    plt.imshow(data); plt.colorbar(); plt.savefig('file.tiff') is creating a matplotlib figure, showing the data stored in data and then using the default parameters (dpi etc.) to save the figure as a tiff. Both syntaxes are correct, it depends on what your use case is.