Shooting with a high ISO sensitivity naturally creates noisy images. We all know that. And removing that noise in post-production is difficult and impacts image quality. But there is actually a way to reduce the noise greatly even in high-ISO images with very little impact on the details in your image. And this technique does not require any noise reduction software or plugins.
The trick that Andy Astbury shows you in this video is based on the idea that image noise is random. If you shoot multiple photos of the exact same scene, this allows Photoshop to even out the differences created by the noisy pixels and the pixels that are actually representing the color or brightness of the scene. The technique used to achieve this, is based on creating a Smart Object and setting its stacking mode to Median.
So, next time you’re faced with a high-ISO situation, try to shoot a whole series of images (the more the better) with the exact same framing and the exact same settings.
My tip: This method is especially useful if you have to shoot in dark environments hand-held. But keep in mind that you need to align all your photos in Photoshop before you can apply this technique. Due to the limited accuracy of the alignment algorithms in Photoshop, image quality starts deteriorating if you use too many hand-held photos for this trick. You have to experiment to find the best number.
If you shoot two photos of exactly the same scene, the actual noise pixels will be in different places in the shots. That means that, if you shoot a whole series of photos of that scene, Photoshop will be able to pick those pixels that are not noisy and discard the rest. That is, for each pixel of your image, it only needs to compare all the instances of that scecific pixel in all the photos and take the one that has a medium brightness. All the noisy pixels that Photoshop discards are either brighter or darker than that.
The actual details in the image are not random and will sty in the same place while the noise changes between the shots. Thus, the more images you shoot, the better Photoshop will be at removing the noise and restoring the actual pixel data.