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iPhone 5s White Balance and Using JPEG vs DNG

I wondered if the iPhone 5s could make a good image under studio lighting, so I set up a FotoDiox DY-200 LED light source* and gave it a try. My Nikon D800E produces superb images under this lighting.

As far as I know there is no control over white balance with the Apple iPhone camera app, and it is JPEG only, so one has to accept the results as-is. Other camera apps might allow more control.

As shown, under daylight balanced lighting, the iPhone 5s makes an image with a strongly yellow and magenta cast. Every frame of a dozen showed this same strong color cast.

I’m not saying the iPhone 5s cannot take good pictures—surely it can under many conditions. But I am saying that this is near ideal lighting and yet the 5s produced a very poor result in terms of color balance. It is what is is: a single test which ought to produce excellent results. There are plenty of mixed-light and artificial light scenarios where the ability to make an accurate white balance is important. It appears that the camera was fooled by the strong colors in this test scene.

Sharpness is pretty decent for a JPEG image, on the order of a mid-grade consumer camera, so that can be said to be a plus. Applying some sharpening it looks decent. But it’s clear that it suffers from loss of fine details from the processing and JPEG conversion; the detail rendition looks like the same marginal stuff found in most all digital cameras—fair enough in context.

Noise is very high in the blue and cyan tones, the red channel is blown out, yellow highlights are blown, and on top of that color gamut is clipped to sRGB thus flattening and utterly destroying any tonal range or subtlety in the reds. Overall, this is a low grade image that will satisfy a lot of users. But not me.

What a shame that Apple does not see fit to let users choose AdobeRGB color space and to set the white balance, which would hugely improve the results here. Or is that possible, and I am something? Probably another camera app would do better, so I’ll have to look into that.

* My Gossen Color Pro IIIf color meter reads 6000°K +10M, meaning that the light is slightly blue and slightly cyan. Applying a 10CC magenta filter shows a neutral tint when measured that way.

iPhone 5s under 6000°K daylight balance LED lighting, Apple camera app JPEG

Next I tried Digital Negative app, which allows shooting into DNG format. I then converted the file to 16-bit TIF in ProPhoto RGB. There is no Adobe profile for the iPhone 5s, so various aspects of contrast and color would have to be hand-tuned. I did add a little saturation here.

The white balance is far better by using the gray card to set it correctly and it appears that using DNG preserves more fine details. But the color gamut remains truncated in spite of converting into the ProPhotoRGB color space. In spite of a 1.2 stop pull for this image to preserve the highlights, the blue patches are pinned (no detail) and noise is exceedingly high. And this is an ETTR exposure.

Sharpness is similar to JPEG but seems to preserve more fine details in spite of the smaller reproduction ratio here (but detail for both is mangled in a very ugly way in areas of uniform color, like the blue and red geisha robes). Noise remains high and even seems worse from the DNG, probably because of some custom processing inside the camera when shooting JPEG with the Apple camera app (and JPEG also blurs away noise along with small details, noise being fine details after all).

My tentative conclusion is that if one could get the white balance right with the Apple camera app, there is probably only a small advantage to the DNG approach. On the other hand, if Adobe were to offer a profile for the 5s and perhaps some custom processing, there might be real advantages in detail and color gamut and white balance.

iPhone 5s under 6000°K daylight balance LED lighting, DNG conversion

Larry G writes:

You may know this, but it wasn't clear in your write up. The DigitalNegative app doesn't actually store the RAW image data in the DNG file, so all it really does is bypass the JPEG conversion (see the docs https://digitalnegativeapp.files.wordpress.com/2013/03/digitalnegative_manual.pdf).

The color and range are still set by the iPhone.

I've only been playing with it for a few days, but the ProCamera7 app (https://www.procamera-app.com/#) seems to work better than the built in one. It has some white balance controls, which I haven't played with. The big thing I have noticed in limited testing is it gets the exposure correct where as the built in camera app tends towards over exposure. It also lets you set the level of JPG compression.

DIGLLOYD: I did not know that. This explains a few things.


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