[scikit-image] pixel value changes during reading image and showing images using skimage and matplotlib

[Imanol Luengo]

Dear Yuanyuan,

The reason why you are looking at a *color* image is due to the colormaps:

http://matplotlib.org/users/colormaps.html

The default colormap (to map from numbers to colors) is not grayscale, 
as matplotlib is not primarly focus on images, and grayscale is not an 
*adequate* colormap to represent other types of plots.

To properly visualize your image specify a colormap to the plot function:

      plt.imshow(output, 'gray')

Cheers,

Imanol


On 11/12/16 06:46, wine lover wrote:
> Dear All,
>
> I have a tif images, its type is |float32|, shape is |(128*128)| (a 
> grayscale image). All the pixel values are of range |[0.0, 1.0]|
>
>  I am trying to read it using |skimage| and show it on screen using 
> |matplotlib|.
>
> |fromskimage importio importmatplotlib.pyplot asplt 
> output=io.imread(os.path.join(image_path,raw_image_name))print(output.dtype)print(output.shape)print(output.max())print(output.min())plt.imshow(output)plt.show()|
>
> The output image looks like color image instead of gray image as shown 
> originally. I attached the screenshot as the capture-1.jpg.
>
> However, when I read the image using |matplotlib| instead,i.e., 
> |output=plt.imread(os.path.join(image_path,raw_image_name))|. I found 
> that pixel value will become 255 and 0. The dtype is still float32. 
> But when I print output, the pixel values are either 0. or 255.
>
> The output image will become black as shown in the second image 
> (capture-2.jpg). I am confused how does this work? My guess is that 
> there are some dtype changes happening during the reading image and 
> showing image,
>
>
> Thanks,
>
> Yuanyuan
>
>
>
> _______________________________________________
> scikit-image mailing list
> scikit-image at python.org
> https://mail.python.org/mailman/listinfo/scikit-image





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