>
> xnview says it is 128*128*8, but "print
> imread('python-gray.png').shape" says (128, 128, 3), however I suppose
> it should be (128, 128)!
Not sure that this is true, but I guess that xnview is using the third
dimension here to refer to a number of bytes. In this case, it is two
bytes, one for the black/white level and the other for alpha level. When
you import this with imread, the png is converted into a Numpy array. The
default behavior in this case is to create an array which is 128*128*3
because the third dimmension is the (R,G,B) levels, which will all be equal
for a gray scale image. This behavior is probably intentional so that you
don't have to write different code to handle gray/color images.
For python-color.png, it is my fault. xnview says it is 128*128*32, so
> it has alpha channel. Hence "imread().shape =(128, 128, 4)" is right
If the third dimension from xnview is bytes, then yes, you are correct.
btw. imread return array which has value between 0 and 1 for PNG file.
> But for other picture format, the value is 0~255. The manual says
> matplotlib reads PNG only by it self, and other files via PIL.But I
> think it is better to make the returned array consistent.
That is most likely due to the way that PNG and e.g. older JPG are defined.
PNG defines each RGBA value using float32, while older JPG uses uint8.
Therefor, it would not make sense to change the dtype of the image on
import.
Hope that helps.
Ryan
On Thu, Apr 16, 2015 at 10:51 AM, oyster <lepto.pyt...@gmail.com> wrote:
> Firstly, thanks, Fabrice Silva
>
> I have checked my picture files again.
>
> For python-gray.png, now it is attacched here or can be downloaded
> from
> http://bbs.blendercn.org/data/attachment/forum/201504/16/222351w3952n3o9968m9a5.png
> .
> xnview says it is 128*128*8, but "print
> imread('python-gray.png').shape" says (128, 128, 3), however I suppose
> it should be (128, 128)!
>
> For python-color.png, it is my fault. xnview says it is 128*128*32, so
> it has alpha channel. Hence "imread().shape =(128, 128, 4)" is right
>
> btw. imread return array which has value between 0 and 1 for PNG file.
> But for other picture format, the value is 0~255. The manual says
> matplotlib reads PNG only by it self, and other files via PIL.But I
> think it is better to make the returned array consistent.
>
>
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