enomoto celtislab

You are using a tag cloud of the standard, and you do not want to display tags that belong to the category not related to the article. 
Try this widget. 
Based on the category of the display article, this widget gets the tag from the article categories of related range. 
For the article there is no category of post page, etc., or by setting <code>all category</code>, <code>internal link article</code>, it displays the tag by examining the related category. 
If you check the ‘internal link article’, get a category from the internal links to articles.
Select Category related range
<ul>
<li>All Category (unrelated article)</li>
<li>Current article Category</li>
<li>Include child category tree</li>
<li>Include parent category tree</li>
<li>Include internal linked article Category</li>
<li>Exclude Category</li>
</ul>
Other parameters : Display format, Sort by, Order, Font size, Number of tags to display, …
<a href="http://celtislab.net/wp_plugin_DCTagCloud/" title="Documentation in Japanese" rel="nofollow ugc">日本語の説明</a>

DynamicCategoryTagCloud

Displays the tag cloud dynamically from related articles belonging to the category of the display article

Keith S.

The best new feature in WordPress 2.3 is the integration of tagging into the core of WordPress. However, the tag cloud widget & functions that are included leaves a lot to be desired. So, with time on my hands, I decided to whip up my own version of the tag cloud that lets you configure the tag cloud with all the customizations (well, almost, see below) the tag cloud template tag allows.
You can find the plugin home page (and leave comments) <a href="http://keithsolomon.net/ctc/" rel="nofollow ugc">here</a>.
<h3>NOTE</h3>
Development on this plugin has STOPPED! I am looking for someone to take it over. Find more info <a href="http://wp.me/p4xrG-7q" rel="nofollow ugc">here</a>
<h3>Upgrade</h3>
I suggest using the built-in WordPress plugin update feature, but to manually upgrade, follow these instructions: 
1. Deactivate the plugin in the WordPress admin menu. 
2. Delete the existing <code>tag-cloud.php</code> file from the <code>/wp-content/plugins</code> folder. 
3. Upload the <code>tag_cloud</code> folder to the <code>/wp-content/plugins/</code> directory. 
4. Activate <code>Configurable Tag Cloud</code> through the ‘Plugins’ menu in WordPress and add the widget to your sidebar. 
5. (Optional) Add <code>ctc()</code> template tag to your theme. Can be configured either via the Options menu, or via parameters in the template tag.

Configurable Tag Cloud (CTC)

Display a tag cloud customized with your preferences in the sidebar.

DynamicCategoryTagCloud vs Configurable Tag Cloud (CTC)