High Dynamic Range and Tips for Bracketing Photos

[stevet1]

In bracketing photos, what's the best range to use, 2 stops over and under? 1 stop?, 1/3 of a stop?

Does it vary by the scenario? And is there a way I can determine ahead of time how much to use?

Steve Thomas

[Tintype_18]

Here's how I do it: I like to experiment with different settings for a particular scenario. Nice thing about digital is the unlimited number of photos, eliminates wasting film.

[johnrmoyer]

If combining the raw files, each raw file has about 2 stops of additional information that is normally discarded as clipped whites or clipped blacks. In DPP, those 2 stops can be recovered, but no more than 2. 

If combining 16 bit tiffs saved from rawtherapee tthen there are often 3 or 4 stops of additional information in each raw file but sometimes with distorted color information in the bright areas and noticeable noise in the dark areas. The least significant bits have less useful information when looked at by themselves because going from a value of 1 to 2 is a one bit difference but is a doubling in linear space (image will typically be viewed in gamma space).

Depending upon the scene and depending upon what software is used for combining the images, it may be advantageous to use 5 images: -4, -2, 0, +2, +4. Maybe 5 images if combining landscape, moon, and stars. Or if something in the image is moving, then a single image in rawtherapee using all of the dynamic range that is in the raw file. Hugin free software works very well for combining exposure stacks.

A HIF file has 10 bits of dynamic range instead of the 8 in a JPG or the 8 in a default configuration TIFF. HIF is compatible with some HDR televisions. https://en.wikipedia.org/wiki/Rec._2020 https://en.wikipedia.org/wiki/Rec._2100  https://www.itu.int/pub/R-REP-BT.2390  https://en.wikipedia.org/wiki/Perceptual_quantizer  https://en.wikipedia.org/wiki/Gamma_correction https://registry.color.org/rgb-registry/srgb   

[stevet1]

John,

My camera will only do a 3-shot bracket.

Would it be beneficial to do 2 braketed sequences (one at a 2-stop sequence and another at a 3-stop sequence, and them combine all six in an HDR composite?

Or, is that overkill?

Steve Thomas

[johnrmoyer]

3 is usually enough. With the camera on a tripod, you could change the exposure compensation between shots. Positive +2 for shadows, negative -2 for highlights, and no exposure compensation for the middle. Using exposure compensation seems to me easier than doing 2 sets of bracketed shots. The bracketing automates the exposure compensation. 

If your camera will highlight clipped whites or clipped blacks, you can take test photos to decide what exposure compensation to use.

The reason for +2 and -2 is that is what a program like Canon DPP can easily use. DPP is the easiest because it will stack the raw files. If using a program like Hugin, "Hugin uses Enblend for seam blending and Enfuse for exposure fusion of bracketed stacks. See the Enblend website for details". https://hugin.sourceforge.io/  . There are nearly always 10 bits of good data in a raw file and 10 bits instead of 8 bits is 2 stops.

Hugin works well with 16 bit TIFFs. The 16 bit TIFFs could be saved from DPP or from rawtherapee. https://rawtherapee.com/ 

Hugin will automate simple stacks, or with enough effort one can align and stack handheld photos.

Gimp could do the stacking, but it seems to me like more work in gimp. 

Your camera might be able to do the stacking in camera and create a JPG as output.

In DPP https://cam.start.canon/en/S002/manual/html/UG-04_EditImage_0040.html#EditImage_0050_11 "Adjusting Dynamic Range", dragging the input white point to the right to 2.0 adds about 2 stops of dynamic range in the bright areas usually without distorting colors. In doing so, it compresses the color curve so that they will fit in sRGB color space unless you edit in a different color space and then fits them to that color space. https://cam.start.canon/en/S002/manual/html/UG-04_EditImage_0040.html#EditImage_0130_1  

HDR-PQ is only available in DPP if it is available in your camera.  HDR-PQ in DPP is 10 bits. 

[stevet1]

John,

Thanks.

I've never gone as high as a 2 stop bracket. I'll have to give it a try.

Steve Thomas