I'm trying to achieve the "Ghost" effect from http://webcamtoy.com/ using GPUImage.
My understanding is that it would be a two-input filter, with a given time delay between the two frames used. I'd then just add the two frames with 0.5 alpha each.
I've seen how to use the current and previous frames with GPUImage using GPUImageBuffer (example of that in the GPUImageLowPassFilter) but I'm not sure how to set up a time delay between the two frames I want to use.
Any ideas or pointers? I was thinking of creating a custom filter and overriding newFrameReadyAtTime:atIndex: to delay the propagation downstream for the first x frames (where x is the delay in terms of number of frames). Maybe a clean way to do this would be to subclass GPUImageBuffer to automatically stack x frames before piping them out into a 2-input filter.
Thanks!
I think you're on the right track with keeping old frames. For the color effects, you're looking at something like extracting the color channels, using them as input to combine in a blend filter. The key is that the input's values have to add up to the natural color values in the non-changing portions of the video.
Related
I have a simple program that renders a couple of 3D objects, using DirectX 3D 9 and HLSL. I'm just starting off with HLSL, I have no experience with 3D rendering.
I am able to change the texture & color of the models and fade between two textures without problems, however I was wondering what the best way to simply fade a 3D object (blend it with the background) would be. I would assume that it wouldn't be done as fading between two textures (using lerp), since I want the object faded to the entire background, so there would be many different textures behind it.
I'm using the LPD3DXEFFECT as my effect class, DrawIndexedPrimitive as the drawing function in each pass, and I only have a single pass. I'm also using Shader Model 3, as this is an older project.
The only way that I thought it possible would be to simply get the color of the pixel before you apply any changes, and then do calculations on it with the color of the texture of the model to attain a faded pixel. However, after looking over the internet, it does not appear that it's actually possible to get the color of a pixel before doing anything to it with HLSL.
Is it even possible to do something like this using HLSL? Am I missing something that could assist me here?
Any help is appreciated!
Forgive me if I'm misunderstanding, but it sounds like you're trying to simulate transparency instead of using built-in transparency.
If you're trying to get the color of the pixels behind the object and want to avoid using transparency, I'd start by trying to use the last rendered frame as a texture, then reference that texture in your current shader. There may be some way to do it within the same frame - to force all other rendering to go first, then handle the one object - but I don't know it.
After a long grind, I finally found a very good workaround for my problem, and I will try to explain my understanding of it for anyone else that has a smillar issue. Thanks to Alexander Stewart for suggesting that there may be an in-built way to do it.
Method Description
Instead of taking care of the background fade in the HLSL pixel shader, there is another way to do it, using a method called Frame Buffer Alpha Blending (full MS Docs documentation: https://learn.microsoft.com/en-us/windows/win32/direct3d9/frame-buffer-alpha).
The basic idea behind this method is to provide a simple way of blending a given pixel that is to be rendered, with the existing pixel on the screen. There is a formula that is followed: FinalColor = ObjectPixelColor * SourceBlendFactor + BackgroundPixelColor * DestinationBlendFactor, all of these "variables" being groups of 4 float values, in the format (R, G, B, A).
How I Implemented it
Before doing anything with the actual shaders, in my Visual Studio C++ file I have to pass a few flags to my render device (I used LPDIRECT3DDEVICE9 as my device class). I had to set render states for both D3DRS_SRCBLEND and D3DRS_DESTBLEND, which are reffering to ObjectPixelColor and DestinationBlendFactor respectivelly in the formula above. These will be my factors that will be multiplying each one of my object and background pixel colors. There are many possible values that can be assigned to D3DRS_SRCBLEND and D3DRS_DESTBLEND, full list is available in the MS Docs link above, but in order to achieve what I wanted to (simply a way to fade an object into the background with an alpha number going from 0 to 1), I figured out the flags should be like this: SetRenderState(D3DRS_SRCBLEND, D3DBLEND_SRCALPHA); SetRenderState(D3DRS_DESTBLEND, D3DBLEND_INVSRCALPHA);.
After setting these flags, before passing through my shaders & rendering, I just needed to set one more flag: SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE);. I was also able to alternate between TRUE and FALSE here without changing anything else with no rendering problems (although my project was very simple, it will probably cause issues on larger projects). You can then pass any arguments you want, such as the alpha number, to the HLSL shader as a global variable (I did it using SetValue()).
Going back to my HLSL shader, after these changes, passing a color float4 variable taken from the tex2D() function from my pixel shader with an alpha value between 0 and 1 yielded the correct alpha, provided there aren't other issues (another issue that I had but hadn't realized at the time was the fact that my transparent object was actually rendering before the background, so I can only reccomend to check the rendering order when working on rendering projects).
I'm sure there could have probably been a better way of implementing this with the latest DirectX, but my compiler only supports Shader Model 3 and lower.
I want to stitch multiple background images provided by ARKit (ARFrame.capturedImage). (I know there are better ways to do this task, but I am using my custom algorithm.)
The issue is that the live stream does not have locked exposure and thus the color of an object in the scene depends on how I orient my iPhone. This, for example, leads to a wall having very different color in each frame (from white through gray to brown-ish), which creates visible banding when stitching the images together.
I noticed ARKit provides lightEstimate for each ARFrame with the ambientIntensity and ambientColorTemperature properties. There is also the ARFrame.camera.exposureOffset property.
Can these properties be used to "normalize" captured images so that colors of the objects in the scene stay roughly the same throughout time and I don't end up with severe banding?
P.S. I do need to use ARKit, otherwise I would set-up my own session based on the AVFoundation API with my own settings (e.g. locked exposure).
Since all mentioned properties are not settable you can't use them directly to fix an intensity of every stitched image in panorama-360.
But you can calculate a difference of intensity and exposure of each frame and then use that multipliers for CoreImage filters. For instance, exposure difference is as simple as that:
Frame_02_Exposure / Frame_01_Exposure = 0.37
Then use the result as input multiplier for CIExposureAdjust filter.
I am working on a tracking algorithm and one of the earliest steps it does is background subtraction. The algorithm gets a series of frames that represent the video with a moving object and static background. The object is in every frame.
In my first version of this process I computed a median image from all the frames and got a very good background scene approximation. Then I subtracted the resulting image from every frame in video sequence to get foreground (moving objects).
The above method worked well, but then I tried to replace it by using OpenCV's background subtractors MOG and MOG2.
What I do not understand is how these two classes perform the "precomputation of the background model"? As far as I understood from dozens of tutorials and documentations, these subtractors update the background model every time I use the apply() method and return a foreground mask.
But this means thet the first result of the apply() method will be a blank mask. And the later images wil have initial object's position ghost in it (see example below):
What am I missing? I googled a lot and seem to be the only one with this problem... Is there a way to run background precomputation that I am not aware of?
EDIT: I found a "trick" to do it: Before using OpenCV's MOG or MOG2 I first compute median background image, then I use it in first apply() call. The following apply() calls produce the foreground mask without the initial position ghost.
But still, is this how it should be done or is there a better way?
If your moving objects are present right from the start, all updating background estimators will place them in the background initially. A solution to that is to initialize your MOG on all frames and then run MOG again with this initialization (as with your median estimate). Depending on the number of frames you might want to adjust the update parameter of MOG (learningRate) to make sure its fully initialized (if you have 100 frames it probably needs to be higher at least 0.01):
void BackgroundSubtractorMOG::operator()(InputArray image, OutputArray fgmask, double **learningRate**=0)
If your moving objects are not present right from the start, make sure that MOG is fully initialized when they appear by setting a high enough value for the update parameter learningRate.
I'm learning the moving object detection using a sequence of frames.
This is an example of two frames. I need to select moved object in the right frame.
I can subtract one frame from another. In the selected area the result would be none zero => that was a movement in that area. But if u look at the right frame, u could see a background selected as well.
Can I somehow separate the car from the background?
i guess the method, when we collecting the background pixels, and than subtract the image from the background is useless on a two frames, right?
You are right that the method does not work very well with only two frames. The method you describe works best when you have one image with only background, which you can then use to compare with new images to look for movement.
It is possible to calculate the movement of the object with only two frames, but then you probably need more advanced methods, such as optical flow or image registration algorithms.
I am creating a custom button that needs to be able to glow to a varying degree
How would I use these pictures to make a button that 'glows' the diamond when it is pressed, and have this glow gradually fade back to inert state?
I want to churn out several different colours of diamond as well... I am hoping to generate all different coloured diamonds from the same stock images presented here.
I would like to get my head around the basic methods available, in enough detail that I can see each one through and make a decision which path to take...
My tangled efforts so far... ( I will delete all of this, or move it into possibly several answers as a solution unfolds... )
I can see 3 potential solution paths:
GL
it looks as though GL has everything it takes to get complete fine-grained control over the process, although functions exposed by core graphics come tantalisingly close, and that would save several hundred lines of code spread over a bunch of source files, which seems a bit ridiculous for such a basic task.
core graphics, and core animation to accomplish the blending
documentation goes on to say
Anything underneath the unpainted samples, such as the current fill color or other drawing, shows through.
so I can chroma-key mask the left image, setting {0,0,0} ie Black as the key.
this at least secures a transparent background, now I have to work on making it yellow instead of grey.
so maybe I could have started instead with setting a yellow back colour for my image context, then use some CGContextSetBlendMode(...) to imprint the diamond on the yellow, THEN use chroma-key masking to get a transparent background
ok, this covers at least getting the basic unlit image on-screen
now I could overlay the sparkly image, using some blend mode, maybe I could keep it in its current greyscale state, and that would just boost the colours of the original
only problem with this is that it is a lot of heavy real-time blending
so maybe I could pre-calculate every image in the animation... this is looking increasingly mucky...
Cocos2D
if this allows me to set the blend mode to additive blending then I could just composite the glowing image over the original image with an appropriate Alpha setting.
After digging through a lot of documentation, the optimal solution seems to be to use core graphics functions to get the source images into a single 2-component GL texture, and then use GL to blend between them.
I will need to pass a uniform value glow_factor into the shader
The obvious solution might seem to simply use
r,g,b = in_r,g,b * { (1 - glow_factor) * inertPixel + glow_factor * shinyPixel }
(where inertPixel is the appropriate pixel of the inert diamond etc)...
it looks like I would also do well to manufacture my own sparkles and add them over the top; a gem should sparkle white irrespective of its characteristic colour.
After having looked at this problem a little more, I can see several solutions
Solution A -- store the transition from glow=0 to glow=1 as 60 frames in memory, then load the appropriate frame into a GL texture every time it is required.
this has an obvious benefit that a graphic designer could construct the entire sequence and I could load it in as a bunch of PNG files.
another advantage is that these frames wouldn't need to be played in sequence... the appropriate frame can be chosen on-the-fly
however, it has a potential drawback of a lot of sending data RAM->VRAM
this can be optimised by using glTexSubImage2D; several frames can be sent simultaneously and then unpacked from within GL... in fact maybe the entire sequence. if this is so, then it would make sense to use PVRT texture compression.
iOS: playing a frame-by-frame greyscale animation in a custom colour
Solution B -- load glow=0 and glow=1 images as GL textures, and manually write shader code that takes in the glow factor as a uniform and performs the blend
this has an advantage that it is close to the wire and can be tweaked in all sorts of ways. Also it is going to be very efficient. This advantage is that it is a big extra slice of code to maintain.
Solution C -- set glBlendMode to perform additive blending.
then draw the glow=0 image image, setting eg alpha=0.2 on each vertex.
then draw the glow=1 image image, setting eg alpha=0.8 on each vertex.
this has an advantage that it can be achieved with a more generic code structure -- ie a very general ' draw textured quad / sprite ' class.
disadvantage is that without some sort of wrapper it is a bit messy... in my game I have a couple of dozen diamonds -- at any one time maybe 2 or 3 are likely to be glowing. so first-pass I would render EVERYTHING ( just need to set Alpha appropriately for everything that is glowing ) and then on the second pass I could draw the glowing sprite again with appropriate Alpha for everything that IS glowing.
it is worth noting that if I pursue solution A, this would involve creating some sort of real-time movie player object, which could be a very useful reusable code component.