ISO in Photography: What It Does in Samsung Pro Mode

ISO brightens a photo by amplifying the signal after the light has reached the sensor. Think of it as turning up the brightness at a cost to image quality: the higher the ISO, the more noticeable the noise, the grain and blotchy colour you see in photos taken at night or in dimly lit rooms.

ISO is one of the three settings to control exposure, together with shutter speed and aperture. The latter is fixed on phone cameras, so ISO and shutter speed are the only exposure settings you can change. In this guide, we'll take a look at what ISO does, its relation with shutter speed and which values to try first in Pro mode on Samsung Galaxy phones (the ISO is automatically determined by the camera in Photo mode).

What does ISO mean in photography?

The name comes from the International Organization for Standardization, which sets the standard for how sensitive film and digital cameras are to light. ISO 400 film was more sensitive, and needed less light, than ISO 100 film. Digital cameras kept the same numbers, so ISO 400 on your phone gives roughly the brightness that film would have.

ISO isn’t actually changing the sensitivity of your digital camera’s sensor (it’s still gathering the same amount of light no matter what ISO you’re at). It’s changing the amount of “gain,” or amplification of the signal from the light hitting the sensor before it’s processed into an image. The higher the gain, the brighter the resulting image from the same amount of light.

Why high ISO makes photos noisy

That graininess is mostly caused by insufficient light, since the random variation in the (insufficient) number of photons reaching the sensor manifests itself as graininess. When you crank up the ISO setting, you’re amplifying that grain along with the signal. In other words, a grainy picture is simply a picture taken with too little light.

It’s worse with a phone camera because the phone camera’s sensor is much smaller than the sensor in a larger camera, so it gathers much less light overall. The main camera in a Galaxy S25 Ultra has a 1/1.3-inch image sensor, which is about a twelfth the size of a full-frame camera’s sensor; the telephoto cameras have even smaller sensors. To mask the graininess, Galaxy phones use noise reduction and combine multiple frames in Photo mode. But excessive noise reduction can result in a painterly look, particularly noticeable in textures like grass, hair, and cloth.

ISO, shutter speed and stops

As ISO is also measured in stops, an increase of one stop will result in an image that is twice as bright. Therefore to keep an image correctly exposed, if you increase the ISO by one stop you can use a shutter speed that is twice as fast, or if you decrease the ISO by one stop you can use a shutter speed that is twice as slow. Our exposure triangle guide explains the whole balance.

When nothing is moving and your phone is sitting on a tripod, a low ISO will be your friend. On the other hand, to capture a moving dog or child you’re going to need to raise the ISO so you can use a faster shutter speed. A higher ISO also lets you keep the shutter fast enough to avoid blur from shaky hands. Our shutter speed guide has speeds for each subject.

How to set ISO in Samsung Pro mode

1. 1

   Open Pro mode

   Tap ISO after tapping More and then Pro in the Camera app. You’ll see it in a row with shutter speed, exposure, focus and white balance controls.

2. 2

   Pick the lens first

   Pick the camera you’ll use first, because the smaller sensors and apertures of the telephoto and ultra-wide angle cameras will need higher ISO settings to match the brightness of photos from the 1x camera, and they’ll introduce image noise sooner, too. In low light, the 1x camera will deliver the least noisy images.

3. 3

   Set the shutter speed

   Figure out whether a faster shutter speed or a cleaner image is more important, and set the shutter speed accordingly. According to Samsung’s guide to Pro mode, ISO won’t remain set to Auto if you change the shutter speed manually, so you’ll need to change it yourself, too.

4. 4

   Raise ISO until the preview looks right

   Start with the lowest available ISO setting and increase it until you’re happy with the brightness of the image. Any higher and you’ll start to see more noise.

5. 5

   Check at 100%

   Take a test picture, view it in the Gallery app and zoom in on a dark area to see if the noise level is acceptable. If not, you can try lowering the ISO and using a slower shutter speed, or finding a way to add more light to the scene.

Which ISO to use on a Galaxy

ISO in Photo mode and Night mode

In Photo mode the Galaxy picks ISO and shutter speed values for you, selecting a fast enough shutter speed to minimise the chances of hand-shake blur and ramping up the ISO when lighting levels are poor. It also stitches together multiple exposures to form a single picture which helps to mask some of the noise. This is why pictures taken in low light using Photo mode can look less noisy than a single frame taken in Pro mode at the same ISO value.

For handheld pictures taken in poor lighting conditions you’ll generally get better results using Night mode (which according to Samsung merges as many as 30 pictures together to form a single image) rather than Pro mode. However, if you have the Galaxy secured on a tripod, you can make use of Pro mode’s longer exposures combined with a low ISO value, which will record more detail than the Galaxy can achieve by stitching together multiple pictures. Our Night mode guide compares the two.

If you notice that Photo mode picks a high ISO for pictures of moving subjects, Samsung’s Camera Assistant app can set an upper limit. Open Camera Assistant and go to Advanced Photo mode controls, where you’ll find a Maximum ISO setting next to Minimum shutter speed. According to Samsung, both only take effect when you shoot at 12MP. If you set a low maximum ISO, pictures taken indoors get noticeably darker, and if the preview suddenly looks dim, Samsung suggests setting both back to None. Our Camera Assistant guide covers the other options.

How to get cleaner photos in low light

• Where possible, add light before you add ISO: stand closer to a window, switch on more lights, or turn your subject towards the light.
• Steady your phone. If you use a phone tripod, or set your camera on a table or lean it against a wall, you can probably get away with a slower shutter speed and/or a lower ISO.
• Use the 1x lens. This will be the main camera, with the largest sensor and brightest lens, meaning you’ll need to crank up the ISO less.
• For images you’re planning on editing, consider shooting RAW files instead, these can be converted in apps such as Lightroom or Snapseed, giving you full control over how much noise reduction to apply. In Pro mode, you can set this in Camera settings › Photo format › Pro mode picture format.
• Don't brighten a dark photo a lot in editing. Lifting the exposure afterwards brings up the same noise as a high ISO would.

Frequently asked questions