Bitmap contrast issue

When I use the imread function to open a grayscale .bmp image, the contrast displayed is far darker than the original image, which causes problems for image processing. Converting the image to .jpeg eliminates the contrast issue, but I have several thousand images to read and I don't want to have to convert them all. Is there a way to get MATLAB to read .bmp files correctly?

Answer 1

[Sean de Wolski]

Are you sure it's not reading them correctly but you're just viewing a small range?

try:

imshow(imread('example.bmp'),[]); %whole range

Edition:

What class is the bitmap file?

I = imread('example.bmp');
class(I)

and then what class is the corresponding JPG file?

I = imread('sameexample.jpg');
class(I)

[Wesley]

That helps, although it's not quite the same as the contrast on the original image. It should be workable, though-- thank you!

[Wesley]

Bitmap: uint8

JPEG: uint8

Answer 2

[Walter Roberson]

BMP files can have color palettes stored, and indeed must use such palettes when they are less than 8 bits deep. A color palette corresponds to MATLAB's colormap.

[YourImage, YourColormap] = imread('example.bmp');
image(YourImage);
if ~isempty(YourColorMap); colormap(YourColorMap); end