L1 SLC images are generated in 32-bit signed integer format with each pixel represented by two interleaved I&Q 16-bit signed integer samples in the order: IQIQIQ…
L1 GRD images are generated in 16-bit unsigned integer format with each pixel representing a single 16-bit magnitude sample.
I have already created the histogram for an image but I would like to know if it is possible, with SNAP, equalize the histogram to get an image with gray levels uniformly distributed.
this would require calculating a new image because intervals of equal distances will never result in classes of same sizes.
In QGIS there is an option to distribut the colors along of quantiles, which means that each class has the same amount of pixels in it. This is however just visually and doesn’t change the values of your raster.
Hi mast, I think we are running into the same problems. Lets see if we can clear a bit the things up.
Before entering the snappy world, I was taking Sentinel1 SAR images, doing gdal stuf (reprojections etc) and then I was using a histogram equalization from skimage.exposure. That was needed in order to increase the brightness and the contrast of the image. Now, after using snappy SAR methods, noise filtering, calibration and transformation to db, terrain correction etc, I am wondering if this is still needed. Since we compute the logarithm of the true backscattered, we increase the plotted information and hence I do not think we need any more the histogram equalization. Please maybe someone can correct me if I am wrong.
There is though a problem I am facing. After this procedure and plotting in python I have the following plot
It seems that over the ocean the 0 values are not interpreted correctly from the colorbar settings. The interesting part is that if I set vmin vmax in the imshow taken the range that qgis automatically selects then the blurry layer is gone! Original range: -95, 18 selected range from qgis -25, -1. And this is how it looks now
@mast
It is right that SNAP may not be able to equalize the histogram, if you want to equalize the histogram to a uniform distribution you may export your image as geo tiff and do the required operation in Matlab as
Img=imread(‘im1.tif’);
J=histeq(img)
I gave a try to this and got the required histogram