How to Improve Contrast with GHS

In this tutorial, we’ll focus on using GHS software to improve contrast. By understanding how histograms work and identifying areas where contrast is lacking, you’ll be able to make targeted adjustments to enhance your images.

 

The Importance of Contrast

Contrast is often overlooked as an essential aspect of image processing. However, it plays a vital role in making your images stand out. When you’re dealing with poor contrast, you might notice that the image as a whole or perhaps just certain areas of the image appear “flat” or washed out. This can be frustrating, especially when you’ve put so much effort into capturing and editing those moments.

Now, just in case you haven’t setup GHS, check out the GHS website for more information, in particular, how to add the GHS repository to PixInsight. (GHS Astro Website).

 

Histograms Reveal Poor Contrast

Let’s take a closer look at our example images: one with poor contrast (left) and the other with decent contrast (right).

 

In the first image, we can see that the histogram has a “flat” spot around the middle, indicating a lack of contrast. This is where GHS comes in handy – it allows you to target those specific regions and make adjustments to improve the overall contrast. Now, if you are following along, you may notice multiple flat spots or humps in your histogram. That’s okay the techniques we will look at in this tutorial are iterative and can be used to target each region in turn.

In the second image, we notice that the histogram has a smooth tapering edge off towards the right side, which suggests good contrast. Now, processing is often a balancing act, so you may never get a histogram that looks this smooth. Always use your best judgment and decide if further flattening of a hump does more damage than good.

By comparing these two histograms, with reference to the images they represent, we can see that humps and flat spots in the histogram, however subtle, can result in a lack of image contrast.

 

Tips for Improving Contrast with GHS

Now that we’ve identified the importance of contrast and the role of histograms in revealing poor contrast, we can work on improving the contrast of our images. But first we need to understand a few key terms within GHS and what they are going to do to help us.

• Symmetry Point – This is the point we wish to set as the inflexion point for our stretch. This means anything to the left of this point will be pulled to the left and anything to the right of this point will be pulled to the right.
• Local Intensity – This determines how tightly around the symmetry point to apply the maximal stretch, anything with this region will be nonlinearly stretched and anything outside this region will be linearly stretched.
• Stretch Factor – This determines how vigorous the stretch will be.

 

Now let’s dive into some actionable tips for improving it using GHS software.

1. 1. 1. Identify the problem areas: When looking at your histogram, identify the regions where the curve is flat or lacks a clear drop-off. These are likely areas where you can make targeted adjustments to improve contrast.
      2. Use your cursor to mark the centre of the “hump” of one of these flat spots. (As shown in the image to the right). Choose this as your symmetry point in GHS.
      3. Choose a local intensity value, values between 2 and 5 tend to work well here, I prefer the less is more approach.
      4. Begin to increase the stretch factor, which will stretch the image and flatten out the hump. Always keep your eye on the preview, do not forego image quality for increased contrast.
      5. If the histogram stretches too far into the highlights and shadows for your taste then you can use the protect shadows and protect highlights sliders.

   Make small adjustments to your contrast settings and observe how they affect your image, don’t overdo it! This will help you avoid over-correcting and losing important details in the process. GHS allows you to target specific regions of the histogram and make adjustments accordingly, take advantage of this feature to focus on areas where contrast is lacking.

   By following these quick and easy steps and understanding how histograms work, you’ll be well-equipped to tackle poor contrast head-on and create stunning images that captivate your audience.

    

    

    

   Conclusion

   In this tutorial, we’ve explored the significance of good contrast in image processing and provided actionable tips for improving it using GHS. By identifying areas where contrast is lacking and making targeted adjustments, you can take your image editing skills to the next level. Remember to always keep an eye on those histograms – they hold the key to unlocking the power of contrast!