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<p>Dear Yuanyuan,</p>
<p>The reason why you are looking at a *color* image is due to the
colormaps:</p>
<p><a class="moz-txt-link-freetext" href="http://matplotlib.org/users/colormaps.html">http://matplotlib.org/users/colormaps.html</a></p>
<p>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.</p>
<p>To properly visualize your image specify a colormap to the plot
function:</p>
<p> plt.imshow(output, 'gray')</p>
<p>Cheers,</p>
<p>Imanol<br>
</p>
<br>
<div class="moz-cite-prefix">On 11/12/16 06:46, wine lover wrote:<br>
</div>
<blockquote
cite="mid:CAFyUc2CvU9S1apTmmd8xaXTYGY8fv=R_ZL0af+2nGhy1GxUG6Q@mail.gmail.com"
type="cite">
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charset=windows-1252">
<div dir="ltr">Dear All,
<div><br>
</div>
<div>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-size:15px;clear:both;color:rgb(36,39,41);font-family:arial,"helvetica
neue",helvetica,sans-serif">I have a tif images, its
type is <code style="margin:0px;padding:1px 5px;border:0px;font-size:13px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;background-color:rgb(239,240,241);white-space:pre-wrap">float32</code>,
shape is <code style="margin:0px;padding:1px 5px;border:0px;font-size:13px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;background-color:rgb(239,240,241);white-space:pre-wrap">(128*128)</code> (a
grayscale image). All the pixel values are of range <code style="margin:0px;padding:1px 5px;border:0px;font-size:13px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;background-color:rgb(239,240,241);white-space:pre-wrap">[0.0, 1.0]</code></p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-size:15px;clear:both;color:rgb(36,39,41);font-family:arial,"helvetica
neue",helvetica,sans-serif"> I am trying to read it
using <code style="margin:0px;padding:1px 5px;border:0px;font-size:13px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;background-color:rgb(239,240,241);white-space:pre-wrap">skimage</code> and
show it on screen using <code style="margin:0px;padding:1px 5px;border:0px;font-size:13px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;background-color:rgb(239,240,241);white-space:pre-wrap">matplotlib</code>. </p>
<pre class="gmail-lang-py gmail-prettyprint gmail-prettyprinted" style="margin-top:0px;margin-bottom:1em;padding:5px;border:0px;font-size:13px;width:auto;max-height:600px;overflow:auto;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;background-color:rgb(239,240,241);color:rgb(57,51,24);word-wrap:normal"><code style="margin:0px;padding:0px;border:0px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;white-space:inherit"><span class="gmail-kwd" style="margin:0px;padding:0px;border:0px;color:rgb(16,16,148)">from</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)"> skimage </span><span class="gmail-kwd" style="margin:0px;padding:0px;border:0px;color:rgb(16,16,148)">import</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)"> io
</span><span class="gmail-kwd" style="margin:0px;padding:0px;border:0px;color:rgb(16,16,148)">import</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)"> matplotlib</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">pyplot </span><span class="gmail-kwd" style="margin:0px;padding:0px;border:0px;color:rgb(16,16,148)">as</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)"> plt
output</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">=</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">io</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">imread</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">(</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">os</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">path</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">join</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">(</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">image_path</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">,</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">raw_image_name</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">))</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">
</span><span class="gmail-kwd" style="margin:0px;padding:0px;border:0px;color:rgb(16,16,148)">print</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">(</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">output</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">dtype</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">)</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">
</span><span class="gmail-kwd" style="margin:0px;padding:0px;border:0px;color:rgb(16,16,148)">print</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">(</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">output</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">shape</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">)</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">
</span><span class="gmail-kwd" style="margin:0px;padding:0px;border:0px;color:rgb(16,16,148)">print</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">(</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">output</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">max</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">())</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">
</span><span class="gmail-kwd" style="margin:0px;padding:0px;border:0px;color:rgb(16,16,148)">print</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">(</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">output</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">min</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">())</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">
plt</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">imshow</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">(</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">output</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">)</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">
plt</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">.</span><span class="gmail-pln" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">show</span><span class="gmail-pun" style="margin:0px;padding:0px;border:0px;color:rgb(48,51,54)">()</span></code></pre>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-size:15px;clear:both;color:rgb(36,39,41);font-family:arial,"helvetica
neue",helvetica,sans-serif">The output image looks like
color image instead of gray image as shown originally. I
attached the screenshot as the capture-1.jpg.<br>
</p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-size:15px;clear:both;color:rgb(36,39,41);font-family:arial,"helvetica
neue",helvetica,sans-serif"><span
style="font-family:arial,"helvetica
neue",helvetica,sans-serif">However, when I read the
image using </span><code style="margin:0px;padding:1px 5px;border:0px;font-size:13px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;background-color:rgb(239,240,241);white-space:pre-wrap">matplotlib</code><span
style="font-family:arial,"helvetica
neue",helvetica,sans-serif"> instead,i.e., </span><code style="margin:0px;padding:1px 5px;border:0px;font-size:13px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;background-color:rgb(239,240,241);white-space:pre-wrap">output=plt.imread(os.path.join(image_path,raw_image_name))</code><span
style="font-family:arial,"helvetica
neue",helvetica,sans-serif">. 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.</span></p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-size:15px;clear:both;color:rgb(36,39,41);font-family:arial,"helvetica
neue",helvetica,sans-serif">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, <br>
</p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-size:15px;clear:both;color:rgb(36,39,41);font-family:arial,"helvetica
neue",helvetica,sans-serif"><br>
</p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-size:15px;clear:both;color:rgb(36,39,41);font-family:arial,"helvetica
neue",helvetica,sans-serif">Thanks,</p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-size:15px;clear:both;color:rgb(36,39,41);font-family:arial,"helvetica
neue",helvetica,sans-serif">Yuanyuan</p>
</div>
</div>
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</blockquote>
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