Photography & Image processing notes

Using the histogram to avoid clipping your highlights and shadows

Jovan Stosic November 4, 2023

What the Histogram looks like

Histogram example

Histogram example

Shadows, Midtones, Highlights

Far left to 0 indicates how much shadow detail is present
Far right to 255 indicates how much highlight detail is present
The midway point indicates how much midtone detail is present

Anything beyond 255 is completely white with no detail present. Anything below 0 is completely black with no detail present.
You can also think of these as colours:
Shadows = Black or dark colours
Midtones = Grey or muted colours
Highlights = White or bright colours

The height of each line represents the amount of pixels in your image that contain that tone. So for example, the big peak shows there are a lot of pixels containing the tonal value. Notice also that on the far left there is an area with no lines. This means that there are no pixels with those tonal values. So there are no dark shadows from 0 to about 10.

https://blog.ianmiddletonphotography.com/2017/12/05/using-the-histogram/

Using the histogram to avoid clipping your highlights and shadows was last modified: November 11th, 2023 by Jovan Stosic

What is an Exposure Stop? How does it affect my Photography?

Jovan Stosic October 9, 2022

What is an Exposure Stop

The “stop” is a unit of measurement used in all aspects of photography. It is used by photographers to determine proper exposures, it is integral to selecting settings on your camera and it makes communication between photographers much easier.

Definition:

An exposure stop is a doubling of a halving of the amount of light one is working with during a particular exposure. It could be the amount of ambient light in a room, it could be the amount of light we are adding to a scene using strobes, it could be the amount of light being allowed to enter the camera.

It is important to note that a stop is not an absolute unit of measure, like a foot, a meter, a gallon, an ounce, etc but rather a stop is a relative unit of measure. It varies dependent on the values we start with. The increase in available light for your photo’s exposure between one wax candle and an additional identical wax candle is a single stop of light, yet the increase between 1 sun and an additional identical sun s is also just a single stop. See? It’s relative to the amount of light we started with.

Example: Here is a working example. Let us pretend we were to be sitting in a completely black room void of light. Now I will lite a single candle.

If I asked you to raise the ambient light in the room by 1 stop, what could you do? You could lite one more identical candle. That would double the amount of ambient light in the room thus raising the available light for our camera by 1 stop.

Now if we wish to raise the exposure of your photograph by 1 stop we have additional options.

Ambient Light: We could still lite the additional candle (or add the exact same amount of light as 1 candle using any kind of light source). That would increase our photo’s exposure by 1 stop.

BUT we could also change the amount of light entering the camera itself (instead of changing the available ambient light in the room). This can be done by manipulating camera settings.

Shutter Speed: We could double the length of time that our shutter is open. (for example 100th/sec to 50th/sec . That would double the amount of light entering the camera and thus increase our photo’s exposure by 1 stop.

Aperture: We could increase the aperture size within our lens by 1 stop. (see below for more on aperture settings). Thus changing the aperture from f/4 to f/2.8 would double the amount of light entering the camera and thus increase our photo’s exposure by 1 stop.

ISO: We could increase the ISO setting by 1 stop (see below for more on ISO settings). Thus changing the ISO from 100 to 200 could double the sensitivity of the camera’s sensor and thus increase our photo’s exposure by 1 stop.

Camera EV (Exposure Value) Settings:

When making exposure value changes (EV) we use stops as our unit of change. In most cases cameras make changes in increments of 1/3 stops; however, this can usually be changed within your camera settings to ½ or 1/1 (full stop) increments. 1/3 provides the most control over your exposure.

The following lists the values you will see when making FULL stop incremental changes for each of our three camera exposure options (aperture, shutter speed, iso)

A change between any of these numbers below will result in a doubling or halving of the light being recorded in our image.

Aperture (measured in “f / stops”):
1.4    2.0    2.8    4.0    5.6    8.0    11    16    22

Shutter speed: (measured in fractions of a second):   
 8th    15th    30th    60th    125th    250th    500th    1,000th

ISO:
100    200    400    800    1600    3200    6400    12800

You will probably recognize these numbers form your camera.

ISO and Shutter speed values are very easy to remember. Just double or halve the starting number (note some very small variations to the rule within shutter speed for example 8th to 15th is not quite a perfect doubling of the number). They are basically intuitive.

Aperture on the other hand, you will just have to commit these numbers to memory as they do not make intuitive sense. The numbers used for are called f-Stops.

Is an “F Stop” the same thing?

No. An f stop (often written as f-stop) is a numerical value that represents the ratio of the lens focal length to the diameter of the entrance pupil. ACK! yes I know. Suffice to say that photographers use these f-stop values to represent changes in “expo

Source: What is an Exposure Stop? How does it affect my Photography?

What is an Exposure Stop? How does it affect my Photography? was last modified: October 9th, 2022 by Jovan Stosic

Stopping down

Jovan Stosic September 19, 2022

Increasing f-stop decreases the aperture of a lens

In photography, stopping down refers to increasing the numerical f-stop number (for example, going from f/2 to f/4), which decreases the size (diameter) of the aperture of a lens, resulting in reducing the amount of light entering the iris of a lens.[1][2]: 112 

Reducing the aperture size increases the depth of field of the image. In the case of film cameras, this allows less light to reach the film plane – to achieve the same exposure after stopping down, it is necessary to compensate for the reduced light by either increasing the exposure time, or using a photographic film with a higher speed. In the case of digital cameras, stopping down the aperture allows less light to reach the image sensor – to achieve the same exposure, it is necessary to compensate for the reduced light by either increasing the exposure time, or increasing the signal gain of the sensor by increasing the camera’s ISO setting. Alternatively, more light can be added to the scene by increasing the amount of light illuminating the scene, such as by using or increasing the strength of electronic flash or other light sources.[3]

As a lens is stopped down from its maximum (widest) aperture, most lens aberrations (spherical aberration, coma and astigmatism) are decreased, but lens diffraction increases. The effect is that for most lenses, the balance between the decreasing aberrations and the increasing diffraction effects of stopping down the lens means that lenses have an optimum aperture for best results, often about three stops closed down from maximum aperture, so for a lens with a maximum aperture of ƒ/2.8, ƒ/8 would be the optimum aperture.[2]: 180

https://en.wikipedia.org/wiki/Stopping_down

Stopping down was last modified: September 19th, 2022 by Jovan Stosic