Always get a 1.0 value

[jossi]

No matter what two images I use the SSIM returned is always 1.0

[jterrace]

Have you tried it with the test images?

[jterrace]

Working for me:

$ pyssim test-images/test1-1.png test-images/test1-1.png 
1.0

$ pyssim test-images/test1-1.png test-images/test1-2.png 
0.998107055283

$ pyssim test-images/test1-1.png test-images/test2-1.png 
0.673010007986

$ pyssim test-images/test1-1.png test-images/test2-2.png 
0.648811237728

[jossi]

I am using 32-bit PNGs so maybe that is the problem? I will try with the test images

[jossi]

bash-3.2$ pyssim test1-1.png test1-2.png
0.998107055283

that works. But not my images.

[jterrace]

Could you post your images?

[jossi]

Note that the images are visually identical, but not bit-by-bit identical. Using a similarity index ImageMagik script I get an index of 0.99884

http://www.fmwconcepts.com/imagemagick/similar/index.php

[jterrace]

I see what's happening. Your images are RGBA and the alpha channel is all 255 values and all transparent pixels are ignored.

[jossi]

Thanks for the prompt response.
What to do then? Convert the PNGs to another format?

[jossi]

Converting the PNGs from 32-bit to 24-bit resolves it.

$ pyssim Car_source.png Car_ImageWarp.png
0.996363163123

Thank you!

[jterrace]

I just looked up the PNG spec though and it says this:

An alpha value of zero represents full transparency, and a value of (2^bitdepth)-1 represents a fully opaque pixel.

So I'm thinking that we're using the wrong value for transparency. We should treat 0 as transparent and 255 as opaque.

[jossi]

Indeed...

Sent from my iPad

On Oct 10, 2013, at 8:22 PM, Jeff Terrace [email protected] wrote:

So I'm thinking that we're using the wrong value for transparency. We should treat 0 as transparent and 255 as opaque.

[jterrace]

Closing this and opened #5 instead