Layer Stacking In Envi

[Vidyesh Sathe]

Hello My name is Vidyesh Sathe, I am actually working on my Dissertation in Planetary Geology, I am pretty new to Crism Data Set and Analysis of Crism Data. I am using Data set which is frt0001176e_07_if164ds_trr3.img and frt0001176e_07_if164l_trr3.img, i am using both VNIR And IR data. sir I followed the process given in CRISM Demonstration: Data Access, Processing, and Analysis - 3rd Planetary Data Workshop 2012, 

After pre-processing given in presentation, I wanted to Combine both VNIR and IR data. so i followed standard Envi process which is,

Envi-Basic Tool-Layer stacking

I imported both map-projected images of VNIR(S) and IR(L).

But as the result the image was completely Black but the information was present(Spectra information from 0.5-3.9)

I will be really grateful  if you can explain to me what i am doing wrong, and what should  I do to correctly project the image. 

Thank You.

[Feng]

Hi Vidyesh,

I download these two data and processed the exact same way as you described but didn't find any problem. Your processing looks fine. One thing you may look at is the header file of the stacking image. The blank in your image could be the data_ignore_value in your header. Would you please compare the header file with mines:

ENVI
description = {
  Create Layer File Result [Tue Dec 17 09:47:59 2019]}
samples = 751
lines   = 634
bands   = 518
header offset = 0
file type = ENVI Standard
data type = 4
interleave = bsq
sensor type = Unknown
byte order = 0
map info = {MRO Mars Equirectangular [IAU 2000] [-35.00N; -39.88E], 1.0000, 1.0000, -6787.3851, -2187402.8323, 1.8000000000e+001, 1.8000000000e+001, D_Mars_2000_IAU_IAG_custom_sphere_lat35, units=Meters}
projection info = {17, 3389570.0, -35.000000, -39.880000, 0.0, 0.0, D_Mars_2000_IAU_IAG_custom_sphere_lat35, MRO Mars Equirectangular [IAU 2000] [-35.00N; -39.88E], units=Meters}
coordinate system string = {PROJCS["MRO Mars Equirectangular [IAU 2000] [-35.00N; -39.88E]",GEOGCS["GCS_Mars_2000_IAU_IAG_custom_sphere_lat35",DATUM["D_Mars_2000_IAU_IAG_custom_sphere_lat35",SPHEROID["Mars_2000_IAU_IAG_custom_sphere_lat35",3389570.0,0.0]],PRIMEM["Reference_Meridian",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Equidistant_Cylindrical"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-39.88],PARAMETER["Standard_Parallel_1",-35.0],UNIT["Meter",1.0]]}
wavelength units = Nanometers
data ignore value = 6.55350000e+004
band names = {
 Layer (Band 1:frt0001176e_07_if164s_trr3_corr_p.img),
 Layer (Band 2:frt0001176e_07_if164s_trr3_corr_p.img),

.....

Also I am using CAT 7.4 in ENVI 5.5 standard (not classic version) to process data. This may be another difference between us.

Please let me know if the problem is still there after you check the header or reprocessed in ENVI 5.5 standard.

 

Thanks,

Feng

 

[Vidyesh Sathe]

Thank you very much for your reply,  as you mentioned above the data_ignore_value in  header was none in my case. I replaced the value with your data_ignore_value and the image was generated. Again I am really grateful for your quick response and for helping me out. Can you please explain to me what actually happened when I replaced the data_ignore_value in the header, that will be really helpful. 

Thank you. 

[Feng]

Hi Vidyesh,

A data ignore value is a designated pixel value that ENVI should ignore when processing an image or computing statistics.

When CAT processing these image, it sets the noData as 65535. If the  data ignore value is not set as 65535, when ENVI display these images, it displays the whole data range (i.e. from 0 to 65535). So the input histogram for each color (RGB) is from 0 to 65535, the output display will arrange them from 0 to 255. Since most values data are close to zero end not the 65535 end, it returns 0 (for each color i.e. RGB) on the output display instead of a value between 0 and 255. So ENVI now displayes a image which has R=0, G=0, B=0. which is actual a black image.  Hope this helps.

 

Thanks,

 

Feng