Chroma Key Lab

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Misc

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Questions?

Chroma Key Lab

Note: if you take your own subject and/or background pictures, subject and background have to have the same dimensions. You can crop or scale photos in, e.g., ImageJ; see me if you want help.

Also note: The One Button Studio is reserved for us, so you can take pictures there if you want. Either video from which you extract a frame (I’ll help if you can’t figure out how to do this from Matlab documentation) or take still photos while the studio is recording video and ignore the video.

If you want to get a sense for the range of color values in a screen, you can use various image processing programs to sample the colors, or you can use Matlab to pick appropriate parts out of the image as an array. For example

>> me = imread( 'Baldwin.jpg' );
>> imshow( me )
>> me( 1:5, 1:5,: )
ans(:,:,1) =
    206  199  133   61   32
    208  201  132   51   28
    204  200  132   54   29
    206  199  132   50   31
    208  199  131   47   31

ans(:,:,2) =
    210  215  173  121  109
    210  217  172  111  107
    208  215  173  113  107
    209  214  172  111  109
    213  215  174  109  112

ans(:,:,3) =
    193  204  173  131  127
    196  207  172  122  124
    194  208  177  127  127
    198  209  180  129  129
    206  214  180  124  131

Matlab has min and max functions that you can use to quickly get the range of values in a region of an image. But notice that these functions find the minimum or maximum down the columns when applied to matrices, so use them twice to get the minimum or maximum over a whole matrix:

>> sample = me( 1:5, 1:5,: );
>> min( sample(:,:,1) )
ans =
    204  199  131   47   28
>> min( min( sample(:,:,1) ) )
ans =
    28

Next

Strings.

Read textbook sections 7.1 and 7.2.

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