Relief cut depth and suggested stock materials : Update

I am cutting reliefs from photos. I am using Fusion 360 for the processing.
While I am using Fusion for NC paths, the question is still relevant for any NC processing.

Does anyone have a guide line for how deep to cut a relief ?

I realized that during image processing before importing for NC path generation I had saved the file as B&W ( 2 bit ) image. That caused the image to lose most of the grayscale and looked very flat after cutting.

Fusion Example: 1800 x 1400 pixel image that uses 75% of the available grayscale.
I used the Image2Surface addin.
Skipped no pixels, 1 mm step over and 5 mm depth.
I scaled the results by 0.12 in the X and Y axis to get approx 8.5 the Y ( portrait image).
The Z axis I have tried anywhere from .12 to 1 scale.

The short example question should have been on a 7" x 9" relief, how deep a relief cut would show up nicely when carved. I am going with 0.08" on the current attempt

I also had to invert the Add in results for one image and not another.
So interpreting the image ( in grayscale ) is another art form I need to get better at.

I am still trying to determine why some images look better if the dark pixels are interpreted as being higher versus the lighter pixels.

Material.
I am currently using old 1" pine shelves from an defunct men’s store. The wood is clear but the grain is showing a bit too much ( takes away from the display).

So if I wanted to stain the material which wood would you use ?
If I wanted to paint, I assume I would use MDF.

Thanks in advance

I’m not 100% sure I understand what you’re intended result is but I’ll take a stab at it here and see if my info helps you to shed light on your solution.

A 2 bit file (also referred to a bitmap file) only provides 2 levels of z-step (max and min) therefore it is truly a 2 level flat image file when output as a relief.

In a standard 8-bit grayscale file there are 256 values of gray available that will translate into z-steps (vertical movement). If you are clipping out 25% of your grayscale values then you are also losing 25% of your available “detail space” It’s best not to clip the grayscale values if at all possible. Anyway, with the value you list of .08" on your current attempt and clipping 25% of your grayscale value leaves you with about 192 z-steps. If we divide .08/192 the result yields a z-step increment of 0.000416 which I believe is a smaller step than the stepper motors are capable of makeing therefore you will lose depth resolution by being too thin. If you are working with imperial you can manually adjust z-height in steps .001" when jogging the machine, so I don’t know if this is the smallest step the machine can make when working in imperial (I believe the native system for the stepper motors is metric and steps won’t translate to imperial “cleanly”) If we assume that .001" is the smallest step in z we can make when working in imperial measurement then we can assume that if we maintain full 256 levels at .001" each would yield a full detail relief depth of .256".

So in conclusion try to maintain as much grayscale range as you and don’t run your relief thickness less than .256" if you don’t want to lose any depth detail.

Also worth noting is the opposite side of the scenario if you define a height z range, say 2", then those z-steps become large enough increments that you will see the height steps just as you do in additive mfg (3D printing) and they may require sanding or additional machining to remove them { 2" / 256 steps = 0.00781" per step}

Well said, thank you !
I like the basic math analogy and example.

The image I am trying to work with is of my granddaughters while they are locked into the TV.
The face areas are limited in grayscale values, except for the eyes and hair. There is lighting effects that makes for additional concentrated height changes.

I trimmed the gray scale to limit the effects of strong dark and light values in those areas.
If not, there is significant height changes that looked bad.

Thanks again

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