Problem with Imhist method (2024)

Just to add, I often use 12 bit images. Occasionally I will use the sum of 3, 12 bit images, so I need the capability to handle both. I would like to limit the number of bins to say 100, but have the x-axis represent the actual intensity, with the max of the x-axis being soemthing related to the max value of intensity in data set

% we have some image which is properly-scaled for its class

inpict_u8 = imread('cameraman.tif');

N = 256; % imhist() default

% here, we're working in uint12-scale, but we don't have a uint12 numeric class

% so we have to create a mis-scaled image in something wide enough (e.g. uint16)

ir = [0 2^8-1];

or = [0 2^12-1];

scalefactor = diff(or)/diff(ir);

inpict_u12 = cast((double(inpict_u8) - ir(1))*scalefactor + or(1),'uint16');

% IPT imhist() needs images to be scaled properly for their class

% both axes limits and bin location get determined by class,

subplot(4,1,1)

imhist(inpict_u8,N) % works with uint8-scale uint8

title('IPT imhist() works with a properly-scaled image')

% so adjusting xlim alone isn't enough to fix imhist() when the image is mis-scaled

subplot(4,1,2)

kscale = 2^16/2^12; % interval scale factor (this cannot always be correct)

Nadjusted = N*kscale; % need to use more bins to have the same density

imhist(inpict_u12,Nadjusted)

xlim(or) % need to reset the xlimits obviously

ylim(ylim().*[1 sqrt(kscale)]) % but we need to rescale ylimits too!

title('Trying to make IPT imhist() work with an improperly-scaled image')

% that's okay, but try it with small N and you'll find out how wrong the scaling factor gets.

% since N and Nadj must both be integers, it's not always possible to adjust N to compensate for scale.

% ... and the colorbar is still wrong.

himg = findobj(gcf,'type','image');

set(himg(1),'cdata',kscale*get(himg(1),'cdata')); % not quite, but close.

% this will need extra work in older versions.

% if you're going to just live without the colorbar,

% you could reinvent the wheel using histc()/histcounts() and stem().

% that would arguably be less work than trying to fix imhist().

subplot(4,1,3)

os = 0.5*diff(or)/(N-1);

breakpoints = linspace(or(1)-os,or(2)+os,N+1).';

centers = linspace(or(1),or(2),N).';

counts = histcounts(inpict_u12,breakpoints);

stem(centers,counts,'marker','none');

xlim(or);

ylim([0 2.5*sqrt(counts*counts.'/numel(counts))]); % this is why we had to rescale before

title('It''s easier to just use histcounts() and stem()')

% but i already did all that.

% MIMT imhistFB() has a bunch of extra functionality that imhist() doesn't.

% it does this sort of thing easily.

subplot(4,1,4)

imhistFB(inpict_u12,N,'range',or) % MIMT's imhist() replacement

title('But MIMT imhistFB() is easiest')

% we have some image which is properly-scaled for its class

inpict_u8 = imread('cameraman.tif');

inpict_i16 = im2int16(inpict_u8); % imhist can do int16

N = 256; % imhist() default

% here, we're working in int12-scale, but we don't have a int12 numeric class

% so we have to create a mis-scaled image in something wide enough (e.g. int16)

ir = [0 2^8-1];

or = [-2^11 2^11-1];

scalefactor = diff(or)/diff(ir);

inpict_i12 = cast((double(inpict_u8) - ir(1))*scalefactor + or(1),'int16');

% IPT imhist() needs images to be scaled properly for their class

% both axes limits and bin location get determined by class,

subplot(4,1,1)

imhist(inpict_i16,N) % works with int16-scale int16

title('IPT imhist() works with a properly-scaled image')

% so adjusting xlim alone isn't enough to fix imhist() when the image is mis-scaled

subplot(4,1,2)

kscale = 2^16/2^12; % interval scale factor (this cannot always be correct)

Nadjusted = N*kscale; % need to use more bins to have the same density

imhist(inpict_i12,Nadjusted)

xlim(or) % need to reset the xlimits obviously

ylim(ylim().*[1 sqrt(kscale)]) % but we need to rescale ylimits too!

title('Trying to make IPT imhist() work with an improperly-scaled image')

% that's okay, but try it with small N and you'll find out how wrong the scaling factor gets.

% since N and Nadj must both be integers, it's not always possible to adjust N to compensate for scale.

% ... and the colorbar is still wrong.

himg = findobj(gcf,'type','image');

strimg = kscale*(get(himg(1),'cdata')-0.5)+0.5;

set(himg(1),'cdata',strimg); % not quite, but close.

% this will need extra work in older versions.

% if you're going to just live without the colorbar,

% you could reinvent the wheel using histc()/histcounts() and stem().

% that would arguably be less work than trying to fix imhist().

subplot(4,1,3)

os = 0.5*diff(or)/(N-1);

breakpoints = linspace(or(1)-os,or(2)+os,N+1).';

centers = linspace(or(1),or(2),N).';

counts = histcounts(inpict_i12,breakpoints);

stem(centers,counts,'marker','none');

xlim(or);

ylim([0 2.5*sqrt(counts*counts.'/numel(counts))]); % this is why we had to rescale before

title('It''s easier to just use histcounts() and stem()')

% but i already did all that.

% MIMT imhistFB() has a bunch of extra functionality that imhist() doesn't.

% it does this sort of thing easily.

subplot(4,1,4)

imhistFB(inpict_i12,N,'range',or) % MIMT's imhist() replacement

title('But MIMT imhistFB() is easiest')

% we have some image which is properly-scaled for its class

inpict_u8 = imread('cameraman.tif');

N = 256; % imhist() default

% use int32 this time instead

ir = [0 2^8-1];

or = [-2^11 2^11-1];

scalefactor = diff(or)/diff(ir);

inpict_i12 = cast((double(inpict_u8) - ir(1))*scalefactor + or(1),'int32');

imhistFB(inpict_i12,N,'range',or) % still the same

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