PNG image created in Matlab shows up as all black in imshow

Hello,

I wrote some Matlab code that deBayers an image and writes the new RGB image out as a 3 x 16-bit png file:

     imwrite(deBayeredImage, outputFileName, 'png', 'Bitdepth', 16);

Although the values are encoded as 16-bit, the actual range of values is 12-bit (ie, 0-4095).

If I load the image using A = imread('image.png'), the values appear reasonable. However, if I try to display the file using imshow (imshow(A) or imshow('image.png'), the display is all black, even though clicking on pixels in the figure shows the RGB values.

I thought that maybe I needed to reset the scale, but imshow(A, [0 4095]) does not change the all-black display.

Any idea what is going on?

Answer 1

[Oliver Woodford]

If you read the imshow help text, you'll see that the range only applies to grayscale images. Try:

   imshow(double(A)/4095);

or

   imdisp(A, [0 4095]);

where imdisp can be found on the File Exchange.

[Megan]

I thought that Matlab could handle png images with integer values if they were 8 or 16 bit. Is that just for writing/reading?

[Oliver Woodford]

Yes. Because a png is an image file. The image array is not a png.