how to save image in png format by keeping data values?

hi...i apply dwt on redchannel of an image and after that i change pixel value of hh and hl bands and apply idwt and after obtain new image i save it in png format. in extraction part the value of hh band is correct but HL band has changed.Why is this happening?while png format is losseless

[Image Analyst]

Is HL integer or floating point? (Sorry, I'm not that familiar with wavelets.) And can PNG handle floating point - I don't know since I only use PNG for integer images.

[Jack Moriss]

my image is double and this problem happen when i use 2 band or alpha channel

Answer 1

[Image Analyst]

Why do you need PNG format? If you just need to recall it in MATLAB, use a .mat file. Otherwise, if other programs, like Photoshop need to use it, then convert it to uint8.

image8 = uint8(255 * mat2gray(HLImage));
imwrite(image8, filename);

[Jack Moriss]

it is a steganography project and i need to save it in one of image format but all of them loss information