Blurry RTI Files

[depeta]

Dear Community,

we are currently working with an RTI dome and have problems with the processing of our data, which results sometimes in blurry RTI files. 

We use a Sony Alpha 7R camera, which is fixed and mounted above the dome. We take pictures with a fixed lens (prime lens, Sony Carl Zeiss Sonnar 35mm). In my opinion the jpg results are high resolution, but after processing the data in RelightLab 2023.02 and 2024.01 the RTI files are somehow very blurry. 

I would love to know what mistake i made during the workflow. Here are some things i thought about:

• maybe our shiny balls are too small, would it make any difference to use bigger ones?
• the aperture is set to 5, which can cause a little bit of a blurry background in the jpg images
• there is no movement during the capture process, I checked every single image and I cannot see any movement (no camera and no dome movement).

I attach two pictures here. The first one shows the captured jpg image and the second one is the RTI result.

It would be great if anyone has an idea on how to fix this problem. I can give more information if needed.

Thanks in advance.

Best regards

Peter

[depeta]

RTI file

[cdschroer]

Hi Peter - how did you check for movement?  This is the most common cause of blurriness in RTIs - if the images themselves are sharp.  Even the movement of a couple of pixels will affect the result - and the pixels on the sensor are only a few microns.  Working on a sprung floor for example, can create movement when you walk nearby.  A table that is not totally steady, or a tripod or camera stand that allows for even tiny movement of the camera can cause problems.

A way I like to check is in RelightLab - after selecting the spheres - then I check the first image and the last image.  The circle around the spheres should still line up.  This will tell you if you had any movement of the camera relative to the scene.  If the subject moved, and the sphere's didn't (perhaps it rocked a small amount on whatever base you are using) then this wouldn't tell you - but you could try checking the first and last images in RelightLab - or in photoshop layers.  You need a reference to check against - such as a ruler - because the movement could be very small.

 

I know you are using a prime lens - because sometimes the lens can "creep" when the camera is pointing down. This can happen for focus as well.  So, make sure you aren't getting any focus change from the first to the last image.  If you use the Digital Lab Notebook - the Inspector tool will check for a change in the "Approximate focus distance" which can be found in the EXIF metadata.  You can also check that by hand using EXIFTool, or showing all info in Bridge or Adobe Camera Raw - again, I would compare the first image to the last image in the sequence.

Carla

[depeta]

Hi Carla,

Thanks for your detailed reply! I think I will try the things you mentioned. I am not absolutely sure that there is no movement - so far I have checked with the ruler tool in Photoshop and compared every single image, but still there could be something like "micro-movement"...

But just to be sure, the blurry result has nothing to do with my camera settings (aperture 5) or the small hemispheres?

Peter

[cdschroer]

The size of the spheres, should Ideally be 250 pixels in diameter to get the most accurate light positions.  But having smaller spheres than that wouldn't impact the resulting RTI in a visible way - would just mean less accurate light positions.

If the area of the subject you are interested in is sharp at aperture 5 - that's what matters.  Aperture choice is going to be based on getting sharp focus for the subject in your setup.  Sometimes the power of your light can dictate aperture choices as well.  I have seen the dome you have, and the LEDs are not very powerful - so going to a wider aperture, and/or taking a longer exposure may be necessary.  If you are using a longer exposure, or a high iso - that could be introducing noise - which would impact the result.  Zoom a photo up to 400% and see if you are seeing any visible noise.

Carla

[depeta]

Thanks a lot for the support! I think that I have a better understanding of our RTI results.

Peter