Introduction to photography

Progress: Chapter 1 of 5 20%

🎯 Learning Objectives

By the end of this chapter, you will be able to:

  • Understand the concept of Ground Sampling Distance (GSD) and why 1mm/px is critical
  • Explain how the three exposure parameters (shutter speed, aperture, ISO) affect image quality
  • Use histograms to assess proper blade exposure
  • Understand depth of field and focusing principles for sharp defect detection

⏱️ Estimated time: 15-20 minutes

Introduction

Let’s start with what we want: the goal of a blade inspection is to bring back pictures of the blade to view and qualify possible defects. This requires two things:

Here is a sample of the kind of pictures we desire:

samplessamplessamples
samplessamplessamples

Ground Sampling Distance

These pictures can then be expertised to detect potential cracks or other damages. This provides us with the most important constraint when doing inspections:

📝 Key Concept

We want to detect defects smaller than 1mm. This means that one pixel on the picture corresponds to 1x1mm on the blade.

The precision of the pictures depend on the camera and on the distance between the drone and the blade. If the drone is further than the flight distance that you selected, the quality will be reduced.

schema precision distance The size one of the pink squares correspond to the GSD : the Ground Sampling Distance.

💡 Remember

The first goal of the pilot is therefore to maintain a correct distance between the blade and the drone.

Quiz

What is the target GSD ?

Single answer

  • 1 cm / px
  • 1 mm / px
  • 2 mm / px
  • 0.5 mm / px

What influences the GSD ?

Multiple answers

  • Drone speed
  • Camera resolution
  • Exposure
  • Distance between drone and blade

Why is maintaining the target distance critical during inspections?

Single answer

  • To avoid collision with the blade
  • To ensure the GSD allows detection of defects smaller than 1mm
  • To reduce the wind impact on the drone
  • To maximize battery life

Exposure parameters

The second criteria for picture quality is a correct exposure: the pictures should be neither too dark nor too bright, because defects couldn’t be detected.

Image too darkImage too bright
dark imagewhite image

⚠️ Warning

Both underexposed (too dark) and overexposed (too bright) images will prevent defect detection!

On any camera, three parameters dictate the amount of light which arrives on the sensor : the shutter speed, the aperture and the ISO.

Shutter speed

The shutter speed is how fast a picture is taken. The longer the diaphragm is open, the more light will reach the sensor.

shutter speed

However, if the shutter is open for too long, the image will become blurry become the target moves while it is open.

example motion blur

📝 In Practice

During the inspection, the shutter speed adjusts based on the selected exposure (around 1/1000 s). This directly influences the drone’s speed to prevent image blur.

Aperture

The aperture determines how wide the opening is. The wider it is, the more light arrives.

aperture animation

However, the more open the diaphragm is, the more blurry the image gets. That is how Portrait Mode works.

example portrait mode

⚠️ Important

During the inspection, we want to avoid using a very wide aperture. When flying, the distance between the drone and the blade is not constant and can vary by approximately ±0.7 m. A wide aperture results in a shallow depth of field, so if the actual distance does not exactly match the focus distance, the image can become blurry. Using a smaller aperture increases the depth of field and helps ensure sharp images despite these distance variations.

ISO

The ISO determines the sensitivity of the sensor. We can use a higher ISO to have a brighter image, but it will increase the noise on the image.

example noise ISO

💡 Key Insight

Therefore, a balance must be found between the three parameters: aperture, shutter speed, and ISO. While increasing ISO can help achieve correct exposure, setting it too high introduces image noise, which reduces overall image quality. Even if the blade appears properly exposed, excessive noise can make fine details harder to see and compromise inspection accuracy. For this reason, ISO should be kept as low as possible, and inspections should be avoided in conditions where ambient light is insufficient.

Quiz

What makes the image blurry ?

Multiple answers

  • high ISO
  • high aperture
  • low shutter speed
  • low ISO
  • high shutter speed
  • low aperture

Why is a fast shutter speed necessary during drone inspections?

Single answer

  • To capture more light
  • To increase the depth of field
  • To prevent motion blur from the moving drone
  • To reduce noise in the image

What is the main disadvantage of using a high ISO setting?

Single answer

  • Images become too dark
  • Images become blurry
  • Images show increased noise
  • Shutter speed must be reduced

Histogram

One tool to help you decide is the histogram : it shows the repartitions of the pixels, from the darkest to the brightest.

histogram example

On this example, we can see two peaks : 1 and 2. If we look at the image that the histogram corresponds to:

example image

We can see that:

Here is an animation that shows how the histogram varies with the brightness of the scene. We can see the peak on the histogram (top right part of the image) moving to the right as the image gets brighter.

Quiz

What is the purpose of a histogram in photography?

Single answer

  • To show the shutter speed settings
  • To display the distribution of pixel brightness from dark to bright
  • To measure the distance to the subject
  • To indicate the focus point

Which element must be properly exposed in blade inspection images?

Single answer

  • The background sky
  • The blade surface
  • The tower
  • The ground

Why might a saturated (overexposed) background be acceptable in blade inspection?

Single answer

  • It makes the image more artistic
  • Only the blade needs proper exposure for defect detection
  • It reduces processing time
  • It improves the histogram balance

Additionnaly, the green parts of the image indicate the regions which are saturated (too bright). This does not necessarily mean that the image is too bright though : only the blade needs to be properly exposed. green_saturation

💡 Pro Tip

On the exemple above, the background is colored green because it is too bright, but the rest of the blade is not (except a little spot at the top). This is perfectly acceptable!

On the Cornis Drone App

During the inspection, you do not have to choose the parameters separately, the software will do it for you. There are a set of exposure values, and the pilot has to choose the one which is the most appropriate to the situation. To change the exposure, use the buttons C1 and C2 at the back of the remote.

image C1/C2

Focus

However, even if the pictures are correctly exposed, there is one last thing we need to check : that the focus is correctly done. The focus correspond to the distance from the camera where the image is sharp. Closer or further, and the image becomes blurry.

illustration focus distance

The depth at which the image is sharp is called the depth of field. On the M300/M350, this is about 1m. As discussed earlier, this varies with the aperture used.

To change the focus, find a point with a lot of contrast on the image and double clic it. Make sure that you do not select a white surface, because the camera will be unable to find the correct focus if there is nothing to focus on.

Quiz

What is the depth of field and why is it important for inspection?

Single answer

  • The distance from the camera sensor, it determines exposure
  • The zoom level of the camera, it determines framing
  • The distance range where the image is sharp, it ensures defect visibility
  • The field of view angle, it determines coverage

Why should you avoid selecting a white surface when adjusting focus?

Single answer

  • White surfaces reflect too much light
  • White surfaces lack contrast needed for accurate autofocus
  • White surfaces create lens flare
  • White surfaces affect exposure settings

What is the approximate depth of field on the M300/M350?

Single answer

  • 10 cm
  • 1 m
  • 5 m
  • 10 m

Final quiz

What is the relationship between aperture and depth of field?

Single answer

  • Higher aperture increases depth of field and sharpness
  • Higher aperture reduces depth of field and can cause blur if focus is off
  • Aperture doesn't affect depth of field
  • Lower aperture causes motion blur

Select the parameters that control the exposure of the camera

Multiple answers

  • aperture
  • focus
  • ISO
  • shutter speed
  • resolution

What is the main trade-off when balancing the three exposure parameters (shutter speed, aperture, ISO)?

Single answer

  • File size vs. processing speed
  • Battery life vs. image quality
  • Light capture vs. image artifacts (blur, noise, shallow focus)
  • Coverage area vs. detail level

✅ Chapter Summary

Congratulations! You’ve completed the introduction to photography for blade inspection. Here are the key takeaways:

🎯 Key Points to Remember

  1. Ground Sampling Distance (GSD): Target is 1mm/px to detect defects smaller than 1mm
  2. GSD depends on: Camera resolution and distance between drone and blade
  3. Three exposure parameters:
    • Shutter Speed: Fast speed (1/1000s) prevents motion blur
    • Aperture: Smaller aperture increases depth of field, prevents blur from distance variations
    • ISO: Keep as low as possible to minimize noise
  4. Exposure trade-offs: Balancing light capture vs. image artifacts (blur, noise, shallow focus)
  5. Histogram: Shows pixel brightness distribution, helps assess proper exposure
  6. Focus on the blade: Only blade exposure matters, background saturation is acceptable
  7. Depth of field: ~1m on M300/M350, focus on high-contrast areas

💭 Before moving on…

Make sure you understand:

  • Why maintaining proper distance is critical for defect detection
  • How each camera parameter affects image quality
  • The concept of acceptable trade-offs in exposure settings

Ready for the next chapter on inspection procedures? Let’s go!

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