Reproduce the exact 2D image from 3D?

Question

I took photos of an object with a real camera. I then used computer vision techniques to 3D-reconstruct the object and in the meanwhile estimated the camera pose (locations, pointing direction, etc.). With everything in hand, I imported everything into Blender, and my goal is to reproduce the exact real-world photo with Blender.

There are of course errors in my 3D reconstruction, so by "exact" I mean I shouldn't get "zoomed-in" or "zoomed-out" version of the real image from Blender. Given the fact that the 3D reconstruction of the object is pretty good, I expect to see my 3D model "overlaid" on top of the real object if I align the Blender-output image and my real photo.

During my 3D reconstruction, I set my focal length to 5000, whose actual unit doesn't really matter, as the 3D reconstructed object will just have the same unit.

How should I set my camera parameters, e.g., focal length (how to convert 5000 to Python-Blender's space), sensor size, etc.?

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Here is the image whose view (not sure if this is the correct word?) I want to reproduce exactly.

Here is the 3D scene.

Rendering the scene above gives this.

So you see, it's a zoomed version of the real image. This is unsurprising because I don't know how to set the parameters of the camera... Focal length may be easy -- just needs a unit conversion? What about all the other parameters like sensor size, etc.

Answer 1

Set Focal length to the same value as your actual camera.

5000 sounds way off. Maybe you missed a decimal and it was 50.00?
Most point-and-shoot cameras are between 35 to 50.
Wide angle is lower, 18 - 30. Zoom is 80 - 200.
Just looking at it, I would guess 50.

Scoot your Blender camera to the same distance
from your object as it was in the real world.

After looking at the scene...

File > User Preferences:

Add-ons tab > Import-Export tab

enable Import Images as Planes

N to bring up right-panel

right-click on the 3D Cursor Location
and Reset All to Default Values

Add > Mesh > Images as Planes

select the image you are trying to replicate

then scale it up on the X and Y by 5

go down to the Viewport Shading button
(bottom-center) click Material
so you can see the image.

Be sure to click the Photo-icon
in the top-right panel
so it won't render in your final image.

Click on the Render tab, and under Dimensions,
Resolution:
X: 1800 px
Y: 1000 px

this should give you the proper aspect-ratio
use the Percentage Scale for test renders

select camera, press 0 on your numpad
to go into camera view

set Focal Length to 50

reset camera X rotation to 0
and set Z location to 14

select human.001

Location:
X: 1.0
Y: -0.3
Z: 9.0

Rotation:
X: 0
Y: 180
Z: 180

Material > Add
Surface: Toon BSDF
Size: 1
Smooth: 1

Add > Lamp > Sun
Strength 3

Location:
X: 5
Y: 5

Rotation:
X: -5
Y: 5

Add > Lamp > Sun
Strength 5

Location:
X: -5
Y: 5

Rotation:
X: -5
Y: -5

Click on the light properties

Size: 5
Samples: 8
Max Bounces: 12

Render tab >
Sampling:
Branched Path Tracing - uncheck square
Clamp Direct: 10
Clamp Indirect: 10
Light Sampling: 0.5

AA Samples:
Render: 25
Preview: 0

Samples:
Glossy: 50
rest of 'em: 1

x Sample All Direct
x Sample All Indirect

Pattern: Correlated Multi Jitter