user77484: I have thermal printer from adafruit and when printing images I have problems getting a proper black.
I tried playing with the dot print time and the dot feed time using the setTimes function, but this seem to have no effect.
  unsigned long dotPrintTime = 3000*30L;
  unsigned long dotFeedTime = 2100*30L;
  printer.setTimes(dotPrintTime, dotFeedTime);

Also the setHeatConfig seems to have no effect. I tried different values.
  uint8_t dots = 11;
  uint8_t _time = 120;
  uint8_t interval = 40;
  printer.setHeatConfig(dots, _time, interval);

Here an image of the result:

Is it possible to print fully black the whole width of the paper?

user20245: Thermal printers generate quick pulses of heat to change thermal paper from white to a darker color.  This may require more than the expected amount of current most Arduino project need.
Consider checking the maximum current rating of your power source.  From the Adafruit printer web page regarding using this Mini Thermal Receipt Printer:

This printer in particular requires 5 to 9 Volts, 1.5 Amps current!
That means you will need a fairly beefy supply and you cannot run it
off of USB power. An external adapter is required!

Also consider trying different thermal paper manufactures and colors.
Lastly, consider how you might avoid BPA from thermal paper.

77484: <p>I have thermal printer from adafruit and when printing images I have problems getting a proper black.</p>
<p>I tried playing with the dot print time and the dot feed time using the <code>setTimes</code> function, but this seem to have no effect.</p>
<pre class="lang-cpp prettyprint-override"><code>  unsigned long dotPrintTime = 3000*30L;
  unsigned long dotFeedTime = 2100*30L;
  printer.setTimes(dotPrintTime, dotFeedTime);
</code></pre>
<p>Also the <code>setHeatConfig</code> seems to have no effect. I tried different values.</p>
<pre class="lang-cpp prettyprint-override"><code>  uint8_t dots = 11;
  uint8_t _time = 120;
  uint8_t interval = 40;
  printer.setHeatConfig(dots, _time, interval);
</code></pre>
<p>Here an image of the result:</p>
<p><a href="https://i.stack.imgur.com/iffIS.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/iffIS.jpg" alt="enter image description here" /></a></p>
<p>Is it possible to print fully black the whole width of the paper?</p>
 20245: <p>Thermal printers generate quick pulses of heat to change thermal paper from white to a darker color.  This may require more than the expected amount of current most Arduino project need.</p>
<p>Consider checking the maximum current rating of your power source.  From the <a href="https://learn.adafruit.com/mini-thermal-receipt-printer/power" rel="nofollow noreferrer">Adafruit printer web page</a> regarding using <a href="https://www.adafruit.com/product/597" rel="nofollow noreferrer">this Mini Thermal Receipt Printer</a>:</p>
<blockquote>
<p>This printer in particular requires 5 to 9 Volts, 1.5 Amps current!
That means you will need a fairly beefy supply and you cannot run it
off of USB power. An external adapter is required!</p>
</blockquote>
<p>Also consider trying different thermal paper manufactures and colors.</p>
<p>Lastly, consider how you might avoid <a href="https://www.sciencedaily.com/releases/2014/10/141022143628.htm" rel="nofollow noreferrer">BPA from thermal paper</a>.</p>
