I searched the forum and found nothing related to "setFov" so I am asking here: 1. Does the [`setFov` API](https://docs.luxonis.com/projects/api/en/latest/references/cpp/?highlight=setFov#_CPPv4N3dai18CalibrationHandler6setFovE17CameraBoardSocketf) accept values that differ from the "Camera Datasheet"? If yes, what is the best API or means for reading the acceptable range (for clamping)? If no, why does the API exist? 2. Assuming the answer is yes above, how do I properly apply my `setFov` calls? I currently have the below code working. I can confirm the `GetFov` call returns updated information but the preview image I expect to be modified doesn't reflect the fov change. I assume I need to "apply" the change somehow, but this is where I'm unsure how. ``` int GetFov() { return calibrationData.getFov(dai::CameraBoardSocket::CAM_A); } void UpdateFov(int delta) { int fov = GetFov() + delta; calibrationData.setFov(dai::CameraBoardSocket::CAM_A, fov); } ```

@"erik"#p9658 Thank you for confirming the expected behavior when using `setPreviewSize`. The `setFov` question I originally had is no longer relevant. My crop related questions using your example values are: 1. Is it possible to customize the initial 1080x1080 crop before the preview downscale happens? 2. If not, then what is the next best course of action? My current best guess is that I'll instead need to have a video stream, then use [the `setCenterCrop` API](https://docs.luxonis.com/projects/api/en/latest/components/messages/image_manip_config/#_CPPv4N3dai16ImageManipConfig13setCenterCropEff), and then [the `setResize` API](https://docs.luxonis.com/projects/api/en/latest/components/messages/image_manip_config/#_CPPv4N3dai16ImageManipConfig9setResizeEii) to create a custom 416x416 preview. Any context or performance tradeoff information you can lend or link to is much appreciated.

@"luxd"#p9663 what exactly would you like to customize?

@"erik"#p9665 I am apparently not doing a good job explaining myself 😂 Here's another try: 1. I have a 1080p resolution where the preview is auto cropped as you say (resulting in a 1080x1080 crop that is then auto scaled down to 416x416) 2. I'd like to have a 720x720 centered crop (instead of the 1080x1080) before downscaling. 3. So my previous questions were 1) can I do this using the preview stream or 2) do I have to create a video stream (or some other approach) to get the desired crop I'm looking for?

`setFov` has no effect

luxd

I searched the forum and found nothing related to "setFov" so I am asking here:

Does the setFov API accept values that differ from the "Camera Datasheet"? If yes, what is the best API or means for reading the acceptable range (for clamping)? If no, why does the API exist?
Assuming the answer is yes above, how do I properly apply my setFov calls?

I currently have the below code working. I can confirm the GetFov call returns updated information but the preview image I expect to be modified doesn't reflect the fov change. I assume I need to "apply" the change somehow, but this is where I'm unsure how.

    int GetFov()
    {
        return calibrationData.getFov(dai::CameraBoardSocket::CAM_A);
    }

    void UpdateFov(int delta)
    {
        int fov = GetFov() + delta;
        calibrationData.setFov(dai::CameraBoardSocket::CAM_A, fov);
    }

erik

Hi luxd ,
Could you elaborate on this?

but the preview image I expect to be modified doesn't reflect the fov change.

I don't think preview output is related to FOV (at least for ColorCamera/MonoCamera node).

luxd

erik Maybe this is just a misunderstanding I have with depthai and its APIs.

I have a preview working as expected. I'd like to constrain the preview. I'm testing both setFov and setCenterCrop to do so. I can confirm the values associated with the API calls are changing, but the final preview is not modified. I am expecting the preview to be modified by these API calls. Should I? Or is the preview stream "locked"?

Ultimately, I need the preview stream (or an otherwise small 1:1 crop) for my NN requirements. Right now I'm exploring how I can further modify the image that I send to my NN (via fov and cropping—but I'm open to other ideas).

erik

Hi luxd
setFov and setCenterCrop aren't really related one to another. setFov will set FOV to calibrationHandler (locally, unless you actually flash it to the device), and setCenterCrop will crop a frame (fov doesn't matter) so it fits the aspect ratio selected.

luxd

erik

OK. So it seems I have a misunderstanding and these APIs sounded like they'd be useful for what I'm after.

To reframe the goal, how do I change the preview image (why I'm under the impression cropping is the best fit) while still ensuring this crop still adheres to the desired ratio and pixel dimensions needed in my NN?

I'm newer to depthai but have researched the docs and this forum. I may still have a mental model mismatch, but I expect to be able to modify the image I send to my NN and the preview seemed like the correct path to take.

erik

luxd when you do setPreviewSize() it will crop only so much (on top/bottom or right/left) to match the desired aspect ratio, then it will downscale to given size.
Example: you have a set 1080P resolution (16:9), and you set colorCam.setPreviewSize(416,416). That means it will first crop the image to 1080x1080 (meaning it will crop quite a lot on left and right, in total 36% of width), then downscale 1080x1080 to 416x416. Note that FOV wasn't relevant here.

luxd

erik Thank you for confirming the expected behavior when using setPreviewSize. The setFov question I originally had is no longer relevant.

My crop related questions using your example values are:

Is it possible to customize the initial 1080x1080 crop before the preview downscale happens?
If not, then what is the next best course of action? My current best guess is that I'll instead need to have a video stream, then use the setCenterCrop API, and then the setResize API to create a custom 416x416 preview. Any context or performance tradeoff information you can lend or link to is much appreciated.

erik

luxd what exactly would you like to customize?

luxd

erik I am apparently not doing a good job explaining myself 😂 Here's another try:

I have a 1080p resolution where the preview is auto cropped as you say (resulting in a 1080x1080 crop that is then auto scaled down to 416x416)
I'd like to have a 720x720 centered crop (instead of the 1080x1080) before downscaling.
So my previous questions were 1) can I do this using the preview stream or 2) do I have to create a video stream (or some other approach) to get the desired crop I'm looking for?

jakaskerl

Hi luxd
I'm really not sure why having a 720x720 pre-downscale resolution would be better, but I guess you could set the original sensor resolution to 720p, then setPreviewSize() would crop the frame to 720x720 before downsizing it to 416x416.

Thanks,
Jaka

erik

I'm guessing you want to first crop the 1920x1080 to 720x720, then downscale that to 416x416? If that's the case, you can use ImageManip node, and just stream 1080P into it directly - you can't achieve that with setPreviewSize()

luxd

erik Thank you for confirming.