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Image target color background

October 16, 2014 - 9:52am #1

hello everyone

i have a problem with vuforia , when i use Image Target

i have an image target that is printed on three background with different colors : pink,red,green.

it s exactly the same motif in black for the three target, only the color background change

i made my dataset with my moif on white background.

i build my app and test it

it works well on green Background , pretty well on pink BackGround , and... not at all on red background ..!!!

why ????

 

please help me...... please...

thank for reading me .... and helping me....

 

Image target color background

October 23, 2014 - 12:01am #6

Ok. So, when you say:

equal result for pink and red

is this based on your visual judgement, or have you used some "contrast analysis" tool to confirm that red and pink actuall give the exact same level / quality of contrast (when they are converted to grayscale) ?

To be sure, you can perform a final step to complete the analysis; now that you have the 3 screenshots (in RGB color), could you try and upload each of them to the Target Manager and then check the Star Rating of each screenshot ?   (please upload the RGB color version of the screenshots, do not use the grayscale ones for this test, so that you can let the Target Manager make its own processing on the original color image).

Also, once you have uploaded each screenshot, the Target Manager will also allow you to click on a button "Show Features" and to reveal the features in the image; this would also give you an indication of the (possibly) different contrast between the 3 images.

 

 

 

Image target color background

October 22, 2014 - 8:47am #5

I made the test you propose

my device is an iPad , i did 3 screenshot : one for each color of background.

put them in photoshop and desature image to have a grayscale.

the contrast level is quite the same on each screenshot... so i try another way to make the grayscale :

the 3 screenshots in photoshop and changing the RGB image mode in Grayscale mode for each image:

result : best contrast for the green : the better reponse of vuforia

equal result for pink and red : lower but not so bad.... but lower

I measure the black level of my motif and of my background : the results : about 40 % for each image.

so.....I dont understand !!!

 

is there a way to tell to vuforia plugin to boost image levels before analisys ???

 

 

 

Image target color background

October 22, 2014 - 7:29am #4

Vuforia analyses images on a grayscale basis, but the level of "gray" is not derived from a single channel (e.g. green or red or blue channel);

rather, it comes from some sort of average / combined brightness of all the 3 channels.

The problem I seem to see here is that, while the Image Target is defined from a source image with bright background and neat contrast, the printed cardboards with red background are probably showing a very low contrast when seen through a real camera.

What you could do is to save a device screenshot in which the Camera of your device is looking at the printed Target with the red background; then load this image (the screenshot) into an Image Editor and see if the grayscale of the screenshot exhibits sufficient contrast. If not, that's probably the reason of your issue.

 

 

 

 

 

 

 

Image target color background

October 22, 2014 - 6:50am #3

thanks for your quick answer,

unfortunately, i cant change the color of the target, they are manufactured objects.

i was thinking of a problem of channel ( RGB)

does VUFORIA use only one channel to analyse the image from the caméra , it works in grayscale so, maybe, the grayscale image is obtained with only one channel ( yhe green ) and so, black motif on red background generate a full black green channel, so VUFORIA cant see anything.

do you know if VUFORIA works such a way ?

if yes, is there a way to change this : to generate grayscale with all channel of the RGB image of the camera ?

Image target color background

October 20, 2014 - 12:50pm #2

This could be probably due to a lack of contrast (low contrast) when printing the motif on a red background.

One thing you could try is to brighten up the red background so that it is something like light red or even orange, so that the core image is well visible.

See also:

https://developer.vuforia.com/resources/dev-guide/natural-features-and-rating

 

 

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