Tag Archives: brighten stars

Bump up Those Stars

After publishing the article on the 600 Rule (and why it’s a lousy rule), I was heavily prodded by a reader who insisted that a 4, 5 or six pixel star streak is not noticeable and not to worry. My counter argument is: “it all depends!”  A larger print (greater magnification) will reveal the streak.  But that got me to thinking – and dangerous things happen when I start thinking.

How Do I Boost the Visibility of My Stars?

The obvious answer is to bump up the brightness and the contrast – but that creates other problems – including magnifying the noise. But there is a simple way to boost those stars – at a relatively low image quality cost.  And this method may very well remove some of the dash like appearance of a star in a longish exposure.

Are you ready? In Photoshop duplicate the layer. Select the duplicate layer. Activate the Move tool. Hold down the control (windows) or option (Mac) key and click the up (or down) arrow key exactly once. Photoshop calls this maneuver a “nudge”  Now change the blend mode to Lighten, 100%.

What do you get? Here is the original.



Now watch as we perform the “bump” (cursor over the image to see what was bumped)

[acx_slideshow name=”BumpUp”]

Why Does this Trick Work?

Actually, your first question might be: why doesn’t my image get blurrier? The answer is that it does but you probably won’t notice even if you print the image LARGE. You can counteract blurry by masking off everything that is not sky in the nudged layer.  The reason that the stars seem to be brighter is that you’ve added more bright pixels in nearly the same location. The eye sees more light where every star is. If you look closely you may also notice that some other features get brighter too – the snag (dead tree) at the far right and the waterfall. To see the change in foreground details compare the Original with the Up One images.  Then compare the Up One with the Down One. In the Down One image I masked off any area that is not in the sky and as a result the tree and waterfall brightness do not change.

Perhaps you’re asking a different question like:

PS My thanks to Tiberiu Tesileanu whose questions and comments lead me to experiment with the “bump” strategy.