hdrgen scrip and calibration issues

[Kate Shaw]

Hi there,

I am trying to use my iPhone 4S with a camera app (called Kit-camera) to make HDR images. I can create HDR images with out any problem when I don't use the Kit-camera app, however I don't have much control over the exposure of my images. For this reason I need Kit-camera. However, when I try making a HDR image in pfstools with images from Kit-camera I get a very unusual calibration curve and the dynamic range for my final HDR image is practically non-existent. The image I get is grey with very little detail. The histogram in pfsview is just a narrow bar. My calibration curve is more of a squiggle shape (a bit like an 'S') than a typical calibration curve. Below is one of my hdrgen scripts:

IMG_1751.JPG 16.9492 2.8 200 0

IMG_1752.JPG 16.9492 2.8 200 0

IMG_1753.JPG 16.9492 2.8 200 0

IMG_1754.JPG 16.9492 2.8 200 0

IMG_1755.JPG 16.9492 2.8 200 0

I find it very weird that while the exposures for each of the 5 images are obviously changing, aperture size, exposure time and iso are static! I would like to know if such a hdrgen script is the reason why I am getting an image with a lower dynamic range than any of my individual LDR images. Also, can a hdrgen script for one image set be used on another if the images are taken using the same camera?

Thank you,

Kate

[Lars O. Grobe]

Hi Kate,

it seams that while the exposure is set as intended, the exif header of the file does not reflect this. You can set the exposure in the hdrgen file manually to try this out. If this works, you can try a tool such as exiftool to manually insert the missing fields in the exif header, and re-run the pfscalibration process.

Cheers, Lars.

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[Kate Shaw]

Thanks for your response, Lars.

I have installed exiftool and have had a look at the exif headers of my images taken with KitCamera. I get the same result. The exposure times, aperture, and iso are the same for all the images. I understand this seems to be more of an issue with my app and not pfstools, but if you have any more advice it would be greatly appreciated. 

Thank you,

Kate. 

[Lars O. Grobe]

Hi Kate,

if you know the exposure times, you can use exiftool to add the missing information to the header (it does not only allow to read, but also to modify exif data). Something like

exiftool -ShutterSpeedValue=1/200 -ExposureTime=1/200 myfile.jpg

should allow you to add the missing info - as long as you actually know the exposure time (I did not test this example).

Cheers, Lars.