Matplotlib output image quality

Question

After converting an png-image into a numpy array and back into an png-image the quality is reduced. If you click the second image, you can see it full size. I think the problem is that no anti aliasing or other filters are activated when the converted image is viewed.

Before conversion:

After conversion:

I tried:

plt.imshow(img2, cmap = 'gray')
plt.plot(aa = True)
plt.show()

to activate anti aliasing but it seems to change nothing. Is there a way to make the second image as pretty as the first again?

There are 2 parameters for plots, which should also work for images. You should look at: figsize and dpi. — Mathieu
– Mathieu, Commented Aug 23, 2018 at 17:53
I don't know why but matplotlib reduces image resolution from 704x490 to 562x394. I can plt.savefig('file.png', bbox_inches='tight', dpi =125 ) which yields an image of 703x493 resolution. That being good enough, is there a way to just keep my image resolution during conversion? — Artur Müller Romanov
– Artur Müller Romanov, Commented Aug 23, 2018 at 20:03
@ArturMüllerRomanov 1. Your image have dpi 96, that will be enough. 2. To save image resolution, hide ticks etc. check this answer. — Vadim Shkaberda
– Vadim Shkaberda, Commented Aug 23, 2018 at 20:09

Artur Müller Romanov · Accepted Answer · 2018-08-25 06:25:44Z

0

Well, I think I found the simplest way to do this.

img1 = plt.imread(impath1, format = 'int32')
plt.imsave('test.png', img1, cmap = 'gray')

Produces the exact same image.

answered Aug 25, 2018 at 6:25

Artur Müller Romanov

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