Possible bug: -intensity has no effect on -white-threshold?.

[Dabrosny]

The -intensity setting appears to have no effect on the result of applying some of the operators they are said to affect, for example the -white-threshold operator:

Code: Select all

imh convert rose: -intensity rec709luminance -white-threshold 32768  -format "%[colorspace] %[fx:mean]\n" -write info: roseIntLumINANCE.png
sRGB 0.469752
imh convert rose: -intensity rec709luma -white-threshold 32768  -format "%[colorspace] %[fx:mean]\n" -write info: roseIntLumA.png
sRGB 0.469752

The resulting images appear to be the same (not just their means) but I was expecting them to be different because one uses -intensity rec709lumINANCE while the other uses nonlinear rec709lumA.

Is this a bug?

ImageMagick 6.8.7-0 2013-09-30 Q16 DPC HDRI Cygwin under Win7 64bit

[fmw42]

I get the same results as you. I am using 6.8.7.5 beta Q16

Code: Select all

imb convert rose: -depth 16 -intensity rec709luminance -white-threshold 32768  -format "%[fx:mean] %[colorspace] %[type] %[gamma]\n" -write info: roseIntLumINANCE.png
0.469752 sRGB TrueColor 0.454545

Code: Select all

imb convert rose: -depth 16 -intensity rec709luma -white-threshold 32768  -format "%[fx:mean] %[colorspace] %[type] %[gamma]\n" -write info: roseIntLumA.png
0.469752 sRGB TrueColor 0.454545

It would appear that -intensity rec709luminance -white-threshold is not sensing the linearity for luminance


Same for -black-threshold

Code: Select all

imb convert rose: -depth 16 -intensity rec709luminance -black-threshold 32768  -format "%[fx:mean] %[colorspace] %[type] %[gamma]\n" -write info: roseIntLumINANCE.png
0.216191 sRGB TrueColor 0.454545

Code: Select all

imb convert rose: -depth 16 -intensity rec709luma -black-threshold 32768  -format "%[fx:mean] %[colorspace] %[type] %[gamma]\n" -write info: roseIntLumA.png
0.216191 sRGB TrueColor 0.454545

Though it partially works for -threshold as in my independent bug report

[fmw42]

I believe that currently the way that -intensity rec709luminance works with function other than -colorspace gray, is that it needs to be preceded by -colorspace RGB. The conversion to gamma=1 is not automatic as it is with -intensity rec709luminance -colorspace gray.

Testing in IM 6.8.7.5 beta, I get the following

-black-threshold:

Code: Select all

imb convert rose: -depth 16 -colorspace RGB -intensity rec709luminance -black-threshold 32768  -format "%[fx:mean] %[colorspace] %[type] %[gamma]\n" -write info: roseIntLumINANCE.png
0.136732 RGB TrueColor 1

 imb convert rose: -depth 16 -intensity rec709luma -black-threshold 32768  -format "%[fx:mean] %[colorspace] %[type] %[gamma]\n" -write info: roseIntLumA.png
0.216191 sRGB TrueColor 0.454545

-white-threshold

Code: Select all

imb convert rose: -depth 16 -colorspace RGB -intensity rec709luminance -white-threshold 32768  -format "%[fx:mean] %[colorspace] %[type] %[gamma]\n" -write info: roseIntLumINANCE.png
0.253591 RGB TrueColor 1

imb convert rose: -depth 16 -intensity rec709luma -white-threshold 32768  -format "%[fx:mean] %[colorspace] %[type] %[gamma]\n" -write info: roseIntLumA.png
0.469752 sRGB TrueColor 0.454545