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Author Topic: Testing an iPhone app for RAW image histograms and ETTR  (Read 614 times)


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Testing an iPhone app for RAW image histograms and ETTR
« on: September 21, 2023, 01:54:26 pm »

I have developed an iPhone app for myself (I call it Raw Insight) which displays an image histogram and exposure meter based on the camera RAW image, instead of the preview/jpeg image. I'm testing for public interest. I have a version for testing I can share with a couple people who'd like to kick the tires (more on that below).

The basic workflow is as follows:

1. Connect the camera to your iPhone. Start Raw Insight.
2. Shoot a RAW image.
3. The app automatically downloads the image, and displays a histogram, exposure meter and preview image, all based solely on the RAW image data. The camera preview/JPEG is never used for any analysis.
4. Raw Insight learns the per-ISO white level of your camera's sensor from overexposed images it has seen. Once it has done that, the exposure meter will display the difference in stops between the highlights of your image and the camera's actual white level, when your image is underexposed.
5. Adjust your camera by the number of stops specified by the exposure meter.
6. Shoot again. This exposure should be perfectly ETTR. If not, repeat from step 5.

If your image is overexposed, the exposure meter will indicate that.

There is a visualization of the RAW image which overlays the parts of the image which have clipped highlights in red. This image can be zoomed to 100%, if desired.

For me, Raw Insight substantially reduces wasted time taking needless bracketed exposures, and I can see with complete confidence the actual quality of the RAW image exposure. I'm aware of no camera that has this capability built-in.

If you are interested in trying my app, respond indicating which iPhone and camera you have, along with your version of iOS. Raw Insight requires iOS 16. DM me if you prefer. My first preference for sharing is with someone with a Nikon camera, since I have the most experience testing with Nikon. However, I have also tested with the Sony Alpha 1, Alpha 7r4, Alpha 7r5, Alpha 6400 and the Canon R5.

N.B. Raw Insight requires iOS 16 and a cable connection from phone to camera. If you have an iPhone with a Lightning connector (i.e. an iPhone older than the iPhone 15, which uses USB-C) you must use one of Apple's Lightning to USB Camera Adapters to connect your camera. A regular USB-A or USB-C cable _will not work_ by itself. I've had success using either of Apple's adapters. I use the cheaper one. Both adapters have the same transfer speed. Wi-Fi is not supported. It is too slow and unreliable to transfer multi-megabyte RAW files. I mount my phone on my camera with a cold-shoe phone adapter and use a six-inch cable.

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