matlab - Why does my image disappear after a very small decrement? -

i have image:

i want convert black , white @ small increments, strange thing disappears after 1 increment.

for line

bw_normal = im2bw(img, 0.33); 

i this:

but line:

bw_normal = im2bw(img, 0.32); 

the word disappears entirely, shouldn't happen right? happens image, other image continue show until 0.1.

this @ 0.32

just white space, can please explain this.

im2bw converts image binary (black/white) image. comparing pixels' luminance component threshold value provide second argument. if pixel brigther, made white, if it's darker, made black.

in case, image has 1 color (pretty much). color has luminance component between 0.32 , 0.33, if use 0.33 threshold, of colored portion of image below threshold , made black. if use 0.32, however, if not of image above threshold , made white.

what experience expected behavior since image white background , single color foreground. once "increment" reaches color's luminance, image gone.