Photo stacking to remove noise from high ISO shots

Click photo for large view

This is a sample photo taken without a tripod from Longshan Temple photowalk last week. It was taken at night in ordinary bulb lighting, so the sensitivity went up to ISO 6400. I shoot 5 photo in burst mode at 1/60 sec but processed only 3 photo for stacking in here.

The photo on the left is one of single shot, and right photo is a stacked photo in Photoshop. When compare two photo, notice right one (stacked photo) has much less noise and also color enhanced. Looking at red color in background, you can see the difference clearly.

Why Image Stacking?

It is good habit to use a tripod for night photography but problem is not always possible. For example, some tourist attractions in Europe, churches and museum, strictly prohibit tripod. Even just touching the tripod case, a guard who is ‘Tripod Police’ will come to kick you out. It’s their job to keep tourists or anyone who is not authorized out of the tripod … In here, I describe quick summary of workflow without too much detail explanation.

  • In Lightroom, select the photo you want to stack & go Edit in> Open as layers in PhotoShop
  • Once loaded as separate layers in PS, select Edit> Auto-align layer *
  • Select Layer> Convert to Smart Object
  • Select Layer> Smart Object> Stack> Mean.    That’s all.

  * There are slight differences on the scene because they are hand-held pictures, thus need auto-align which will reduce image blurring

When multiple pictures are stacked, the color of the photo enriched because of signal overlap, meanwhile the noise reduced because noise does not occur in the same place by its nature. Therefore when pixel information averaged (=Mean) random noise become lower while signal is enhanced.

Important remarks

  1. Align and Stacking couple of raw files in Photoshop requires considerable computing power. I use lower spec laptop which is fine with Lightroom but photo stacking does not run well if more than 3 raw file loaded. For complex imaging manupulation, e.g. Photoshop rendering, 3D Graphic or Video work requires big computing load so be prepared or be patient enough…  :- )
  2. Image stacking menu is available on Photoshop CC, CS6 Extended, and CS5 Extended. If not extended version, like CS6 or CS5, does not support this function. It is still possible to  do this, using open source image editing program GIMP or manual stacking on layer with regular version Photoshop**.
  3. Another remark is this technique works only a certain situation. When main subject is moving, it does not work in obvious reason, image overlapped in shifted pixels. In case a small object or light moving at the background, it may work or not depends on photo. The most appropriate scene for this technique is ‘still life’ located at dark area or ‘night cityscape’.
  4. Because the pictures are overlapped, not only the noise is reduced but the sharpness is also lowered. When shoot in handheld, multiple shots can not be perfectly matched, so the border line become blur during the stack process. It is best to train the camera does not move as much as possible, and shoot at least 5 to 7 in burst mode (highest continuous shots) and select best aligned 3 to 5 shots for stacking.

  ** manual stacking is not difficult at all. Will describe later, but limitation is it works only ‘Mean’ while Photoshop auto stacking also working ‘Median’, ‘Maximum’ and many other options

Conclusion

Before this test, I had very high anticipation that might be applicable in universal, but it turns out NOT the case. It has limited application and obvious side effects. However, if there is no way other than high ISO shooting, this is an option to go. When managed properly, it will deliver professional quality photo (low noise, high definition and color saturation) in ISO 6400, 12800 which is un-imaginable without tripod.

 

//

글쓴이 Leo_KHIMME

사진, 사진기, 렌즈, 여행, 새로운 곳, 새로운 기술 & 신산업혁명
대만 타이페이 거주
Oldies but Goodies 오피넛 멤버