Using imwrite() to create a .bmp file with custom colormap

20 次查看（过去 30 天）
Hailey Trier
Hailey Trier 2016-12-24
评论： Dayangku Nur Faizah Pengiran Mohamad 2021-11-16
I am trying to use the imwrite() function to create and save a .bmp file using a custom colormap, 'myMap'. The colormap contains values between 0 and 1 and is a variable of type double with size [51 3]. My image matrix is of type double and contains values 0 to 1. When I produce this image with imagesc() it comes out fine:
figure
imagesc(myImage)
axis equal
axis tight
colormap(myMap)
However, when I use imwrite to save it as a .bmp file the image is saved in all one dark grey color:
imwrite(myImage, myMap, 'grid.bmp')
I have tried converting myImage to uint8 format and scaling myMap into [256 3] size, but neither works. What am I doing wrong? Thanks.

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2016-12-24
The colormap for the imwrite must be in the range 0 to 1.
When you imwrite with a colormap the data must be integral. If it is type double or single then 1 is subtracted from it and the result is converted to uint8. In other words the values must already be colormap indices.
You need:
Numcolor = size(myMap, 1);
Imgmin = min(MyImage(:)) ;
Imgmax = max(MyImage(:)) ;
mappedImage = uint8( (MyImage-Imgmin)./(Imgmax-ImgMin).* (Numcolor-1) ) ;
Then imwrite(mappedImage, myMap,...)

更多回答（1 个）

Image Analyst
Image Analyst 2016-12-25
编辑：Image Analyst 2016-12-25
You can convert your image to RGB with ind2rgb():
rgbImage = ind2rgb(myImage, myMap);
imwrite(rgbImage, filename);
  7 个评论
显示 5更早的评论
Image Analyst
Image Analyst 2016-12-26
Why do you say it's non-image data when she called the variable "myImage", used imagesc() to display it, and tried to save it with imwrite()? As far as I can guess, it's a floating point (double) image. Anyway, my code also normalizes and converts to integer indices like yours, just using an alternate method.
Dayangku Nur Faizah Pengiran Mohamad
Dayangku Nur Faizah Pengiran Mohamad 2021-11-16
Hi. I want ask a question.
How do I save the original image jpg from figure for colormap?
Here my codes:
>> I=imread('M_92_ar_2001743_st01_currentsize_200x200.jpg');
>> imshow(I);
>> imfinfo('M_92_ar_2001743_st01_currentsize_200x200.jpg');
>> I2=I(:,:,1);
>> imshow(I2);
>> map = [0, 0.3, 0
0, 0.4, 0
0, 0.5, 0
0, 0.6, 0
0, 0.8, 0
0, 1.0, 0];
>> imshow(I2);
>> colormap(map);
>> imwrite(I2,map,'cmalignant200.jpg');

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Color and Styling 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by