The two shoo­ting tech­ni­ques discussed in this article are ETTR (Expose to the Right) and HDR (High Dynamic Range).

With ETTR, or expo­sure towards the right, you over­ex­pose as much as possible without getting areas of maximum white. This allows you to use the maximum possible dynamic range of the camera sensor. With HDR, I extend this dynamic range of the camera sensor even further by inclu­ding addi­tional over­ex­posed and under­ex­posed images. Many cameras do this semi-auto­ma­ti­cally with HDR bracke­ting at the touch of a button. 

Why all this?

Dark areas of an image have the charac­te­ristic that they contain all the infor­ma­tion, but if they emit too little light and only a small amount of light ‘falls’ on the sensor, then this amount of light is not suffi­cient to mask the elec­tronic noise of the photo­sensor. If I brighten these dark areas signi­fi­cantly in post-proces­sing, I also amplify the noise in these areas of the image. Yes, even at ISO 100. 

With ETTR, I expose as brightly as possible. (However, I must avoid crea­ting maximum white, as this would result in a loss of image infor­ma­tion at that point!) This allows more light to hit the sensor in the dark areas of the photo, which in turn better masks the noise. When brigh­tening the image in image editing, I still have less noise. The overall image quality improves. 

With HDR, I use the infor­ma­tion from the over­ex­posed image in the dark areas and the infor­ma­tion in the bright areas from the under­ex­posed image. The result is a higher dynamic range than the camera sensor can provide and less noise, resul­ting in higher image quality. 

Expo­sure compen­sa­tion and histogram

For both shoo­ting tech­ni­ques, it is advi­sable to use the camera’s expo­sure compen­sa­tion to achieve the best results. The built-in histo­gram of modern digital cameras allows you to reliably check the expo­sure while shoo­ting. If you want to use the ETTR tech­nique, I turn the expo­sure compen­sa­tion to the posi­tive until the histo­gram shows a steep rise on the right-hand side. This signals over­ex­po­sure and a possible maximum white that cannot be saved in image editing. I demons­trate the proce­dure in the video below. The histo­gram also clearly shows whether all the infor­ma­tion in the image can be captured or whether you need to switch from ETTR to HDR tech­nique. If the histo­gram peaks at the bottom and top, the dynamic range of the camera sensor is not suffi­cient and HDR tech­nique must (should) be used.

Possible sources of error

The histo­gram during shoo­ting shows the entire channel and thus an average of the indi­vi­dual colour chan­nels. In this case, it may happen that the expo­sure looks good and has not been over­ex­posed too far to the right in ETTR. However, in the case of such an intense sunrise, for example, the red colour channel may clip, meaning that colour infor­ma­tion is lost. It is ther­e­fore advi­sable to check the histo­grams of the indi­vi­dual colour chan­nels after shoo­ting and take correc­tive action if neces­sary. Even small, very bright but over­ex­posed areas in the image can prevent the histo­gram from showing an accu­mu­la­tion on the right-hand side, as the area is simply too small in compa­rison to the overall image. The over­ex­po­sure warning helps here.

When crea­ting HDR bracke­ting shots, do not allow too much time to pass between shots. Other­wise, moving elements may cause ghos­ting, i.e. ghost effects in the image. You should also pay atten­tion to colour breaks during inten­sive image processing!