issue with rgb2ind

Hello,

I just leared that back in the day that you could get a camera for your game boy. I was just interested into replicating the style of image that they made. I simply just used the stock pepper image, scaled the image to a multiple of 128x112 and tried to use rgb2ind to convert the image to "greyscale" or a "greenscale". I use indicies that I found but I keep getting a black image. What am I doing wrong?

for reference, this article shows how to create the effect with gimp

https://gameboymaniac.com/how-to-make-a-fake-game-boy-camera-photo/

%% rescale image
Scale_Multiplier = 4;
rescale_size = [112,128].* Scale_Multiplier;
RGB2 = imresize(RGB,[rescale_size(1) rescale_size(2)]);
%% Greyscale or Greenscale
Gray_or_Green = 1;
%% Color image
if (Gray_or_Green ==0) 
    Color_Map = [0,0,0;128,128,128;192,192,192;255,255,255]; % Grey
    Color_Map = Color_Map/255;
elseif (Gray_or_Green ==1)
    Color_Map = [51,57,35;110,121,75;191,201,150;241,246,223]; % Green
    Color_Map = Color_Map/255;
end
X = rgb2ind(RGB2,Color_Map);
imshow(X)

Answer 1

[Walter Roberson]

RGB = imread('flamingos.jpg');

%% rescale image
Scale_Multiplier = 4;
rescale_size = [112,128].* Scale_Multiplier;
RGB2 = imresize(RGB,[rescale_size(1) rescale_size(2)]);
%% Greyscale or Greenscale
Gray_or_Green = 1;
%% Color image
if (Gray_or_Green ==0) 
    Color_Map = [0,0,0;128,128,128;192,192,192;255,255,255]; % Grey
    Color_Map = Color_Map/255;
elseif (Gray_or_Green ==1)
    Color_Map = [51,57,35;110,121,75;191,201,150;241,246,223]; % Green
    Color_Map = Color_Map/255;
end
X = rgb2ind(RGB2,Color_Map);
RGBX = ind2rgb(X, Color_Map);
imshow(RGBX)

[Andrew Luce]

Thank you for the help. The only thing I'm wondering is if that it can change the dithering style to more like this?

[Walter Roberson]

Possibly dither instead of the rgb2ind() call ?

Answer 2

[DGM]

When I was adding gray2pcolor()/uniquant() to MIMT, I thought about this question. I took the time to add dithering modes to both to make this sort of thing possible. I decided to go the extra mile and just make a tool to do this one thing specifically.

MIMT now has gbcam().

inpictrgb = imread('hallway.jpg');
inpict = mono(inpictrgb,'y'); % convert to luma

% it usually helps to play with image brightness/contrast
inpict = imlnc(inpict,'g',1.2,'k',1.2);

scale = 2; % output scaling factor

% tan-tone like a GB pocket
A = gbcam(inpict,'newschool',scale);
% olive-tone like an original GB
B = gbcam(inpict,'oldschool',scale);
% slightly bright with muted extrema (gamma~0.8)
C = gbcam(inpict,'gray',scale);
% the common overly-bright gray map (gamma~0.68)
D = gbcam(inpict,'brigray',scale);
% a strictly linear gray map (gamma=1)
E = gbcam(inpict,'unigray',scale);

% concatenate for easier handling 
outpict1 = [A B];
outpict2 = [C D E];

If you don't like these maps, you can specify your own as a 4x3 unit-scale color table.

% hmm i like that olive map, but i want the midtones brighter
CT = [0 59 61; 24 109 66; 47 160 72; 71 210 77]/255; % the given map
CT = ctshift(CT,0.3); % shift the map distribution

% use your new custom map
A = gbcam(inpict,CT,scale);

Images are automatically centered, scaled, and cropped to fit the output frame. If you want your image located differently, prepare it accordingly prior to feeding it to gbcam().

The functions gbcam(), mono(), imlnc(), and ctshift() are all from MIMT.