What is the different if the value of the image is 0 and 1, and if the value of the image is 0 and 255?

Anyone can explain me on details what is exactly the different if the value of the image is 0 and 1,

then another image is 0 and 255? Is the same idea? Black and white?

Answer 1

[Cris LaPierre]

The range of values, and more particularly, what value corresponds to white, is determined by the data type of your image. What are the data types of your images? If 255 is white, then it is likely you are working with an 8-bit image. A scale of 0-1 tends to be the case when you have converted your image to single or double in MATLAB.

Here, both are binary images. 0 corresponds to black, and 1 or 255 correspond to white.

[Cris LaPierre]

The 'DisplayRange' details on the imshow documentation page states the following on how MATLAB decides what value should be white:

If you do not specify a display range, then imshow selects a default display range based on the image data type.

• If I is an integer type, then DisplayRange defaults to the minimum and maximum representable values for that integer class. For example, the default display range for uint16 arrays is [0, 65535].
• If I is of data type single or double, then the default display range is [0, 1].

.

[Image Analyst]

An image with 0 and 1 values can also be a logical image (false or true respectively). For example

mask = grayImage > someThreshold;
imshow(mask);
impixelinfo; % Let's user mouse around over the image seeing location and value.

[Dayangku Nur Faizah Pengiran Mohamad]

My intention is I want 0 and 255 only in my image. But then, I got like this one, I attach the value of my binary image:

As you can see, some of the value above is 5, 2 1, 6, 238. How can I normalize this image into 0 and 255 only?

My data type is in uint8, 8 bit depth, 512x512 pixels and grayscale image. And I attach you my example image data here.

[Cris LaPierre]

imbinarize can be used to conver your image to a binary image (logical data type), with a range of [0, 1].

You can then use im2uint8 to convert your logical array back to uint8.

img = imread('1qqq.jpg');
img(205:220,185:190)

ans = 16×6

0 255 255 237 255 255 4 0 253 255 255 255 5 0 255 252 255 244 0 6 245 255 253 254 7 0 0 255 252 255 0 14 2 0 238 237 8 0 5 2 255 255 5 0 11 0 0 253 0 4 0 5 13 253 0 22 0 0 9 255

imshow(img)

BW = imbinarize(img);
BW(205:220,185:190)

ans = 16×6 logical array
   0   1   1   1   1   1
   0   0   1   1   1   1
   0   0   1   1   1   1
   0   0   1   1   1   1
   0   0   0   1   1   1
   0   0   0   0   1   1
   0   0   0   0   1   1
   0   0   0   0   0   1
   0   0   0   0   0   1
   0   0   0   0   0   1
   0   0   0   0   0   0
   0   0   0   0   0   0
   0   0   0   0   0   0
   0   0   0   0   0   0
   0   0   0   0   0   0
   0   0   0   0   0   0

img2 = im2uint8(BW);
img2(205:220,185:190)

ans = 16×6

0 255 255 255 255 255 0 0 255 255 255 255 0 0 255 255 255 255 0 0 255 255 255 255 0 0 0 255 255 255 0 0 0 0 255 255 0 0 0 0 255 255 0 0 0 0 0 255 0 0 0 0 0 255 0 0 0 0 0 255

imshow(img2)

[Dayangku Nur Faizah Pengiran Mohamad]

OK, thanks for your help Sir! I got it 0 and 255 value. But I got some problem on how to save the last image which is the value in 0 and 255. Where, I saved it I use the code:

imwrite(I2,'bin8.jpg');

But then, I transfer the bin8.jpg into my folder on pc. And when I read back the image using

imread

Its turned into like this Sir:

Is there any codes should I apply so that the value won't change besides the value 0 and 255?

[DGM]

Do not save binary images as JPG

The content will be damaged, the datatype will be altered, and the filesize will be larger than using a lossless format like PNG. There's no reason to use JPG for a binarized image.

https://www.mathworks.com/matlabcentral/answers/1987548-how-to-convert-logical-form-to-binary-form-image#answer_1261663

https://www.mathworks.com/matlabcentral/answers/182252-resolution-of-a-matlab-created-jpg#comment_2812598

JPG is not lossless, and this isn't Photoshop or GIMP, where you're saving 90% 4:4:4 JPGs. That's not an option. Unless you have carefully considered the damage caused by using a low-quality 4:2:0 downsampled JPG, and you don't intend to ever do any further technical processing of an image, just don't use JPG for anything. That includes when you save figures and plots.

https://www.mathworks.com/matlabcentral/answers/789399-exporting-only-the-plot-legend-to-a-jpg-file#answer_1266448

Another example:

% a logical image
A = imread('1qqq.jpg')>128;
imshow(A)

% save as JPG, read back
fname1 = 'junk.jpg';
imwrite(A,fname1);
B1 = imread(fname1);
% the image class is now uint8
% and the values are spread away from black/white
imhist(B1)
ylim([0 500])

% so we'd have to re-binarize it _every single time_
B1 = B1 > 128;

% save as PNG, read back
fname2 = 'junk.png';
imwrite(A,fname2);
B2 = imread(fname2);
% the image class is unchanged
% the values are exactly the same
% we don't have to do anything.
isequal(A,B2)

ans = logical
   1

% the damaged JPG is 9x as large as a perfect PNG
S1 = imfinfo(fname1);
S2 = imfinfo(fname2);
sizerat = S1.FileSize/S2.FileSize

sizerat = 9.0731