Use https://github.com/ImageMagick/ImageMagick/discussions instead.
https://imagemagick.com/discourse-server/
https://imagemagick.com/discourse-server/viewtopic.php?t=24191
The bug fix to make gamma=1 for the IM gamma (PNG gamma is already 1) seems to have been lost in the current beta.glennrp wrote:Yes, the PNG reader now sets image->gamma=1.0 when it reads a gAMA chunk with gamma==1.0.
Okay, thanks!glennrp wrote:Yes, the PNG reader now sets image->gamma=1.0 when it reads a gAMA chunk with gamma==1.0.
Code: Select all
convert rose_luminance.png -colorspace RGB ....some processing... result.png
But my images were not properly linear since the IM gamma=0.4545convert rose_luminance.png -colorspace RGB ....some processing... result.png
But what I'm asking is, once the fix is (back) in place, and I read into IM a 1-channel linear image properly identified as linear by gamma=1, can I explicitly expand it to a 3-channel linear RGB image via -colorspace so that I can do some further linear processing that will change some of these color channels.fmw42 wrote:But my images were not properly linear since the IM gamma=0.4545
Code: Select all
convert rose_luminance.png -colorspace RGB ....some processing... result.png
Dabrosny wrote: But what I'm asking is, once the fix is (back) in place, and I read into IM a 1-channel linear image properly identified as linear by gamma=1, can I explicitly expand it to a 3-channel linear RGB image via -colorspace so that I can do some further linear processing that will change some of these color channels.
...or will this instead try to "linearize" the data with an sRGB-->RGB gamma expansion even though the gamma=1 indicates that it was already linear?Code: Select all
convert rose_luminance.png -colorspace RGB ....some processing... result.png
Okay, can you try those two with the beta? (even without "...some processing..." for starters).fmw42 wrote: I am not sure, but I believe that it should not matter if you do
convert rose_luminance.png -colorspace RGB ....some processing... result.png
or
convert rose_luminance.png -set colorspace RGB ....some processing... result.png
or just leave it out
...<snip/>...
I would think that IM would know it is linear by the gamma=1 which any of the above would still maintain. Once the image is linear, IM should know and -colorspace RGB will not matter nor will -set colorspace RGB.
But I think it would be best to wait until the bug gets fixed so that I can be sure.
Code: Select all
Image: rose_luminance.png
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see http://www.imagemagick.org/discourse-server/viewtopic.php?f=2&t=24256
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Code: Select all
Image: rose_luminance_1.png
Format: PNG (Portable Network Graphics)
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218: (218,218,218) #DADADA gray(218)
219: (219,219,219) #DBDBDB gray(219)
220: (220,220,220) #DCDCDC gray(220)
221: (221,221,221) #DDDDDD gray(221)
222: (222,222,222) #DEDEDE gray(222)
223: (223,223,223) #DFDFDF gray(223)
224: (224,224,224) #E0E0E0 gray(224)
225: (225,225,225) #E1E1E1 gray(225)
226: (226,226,226) #E2E2E2 gray(226)
227: (227,227,227) #E3E3E3 gray(227)
228: (228,228,228) #E4E4E4 gray(228)
229: (229,229,229) #E5E5E5 gray(229)
230: (230,230,230) #E6E6E6 gray(230)
231: (231,231,231) #E7E7E7 gray(231)
232: (232,232,232) #E8E8E8 gray(232)
233: (233,233,233) #E9E9E9 gray(233)
234: (234,234,234) #EAEAEA gray(234)
235: (235,235,235) #EBEBEB gray(235)
236: (236,236,236) #ECECEC gray(236)
237: (237,237,237) #EDEDED gray(237)
238: (238,238,238) #EEEEEE gray(238)
239: (239,239,239) #EFEFEF gray(239)
240: (240,240,240) #F0F0F0 gray(240)
241: (241,241,241) #F1F1F1 gray(241)
242: (242,242,242) #F2F2F2 gray(242)
243: (243,243,243) #F3F3F3 gray(243)
244: (244,244,244) #F4F4F4 gray(244)
245: (245,245,245) #F5F5F5 gray(245)
246: (246,246,246) #F6F6F6 gray(246)
247: (247,247,247) #F7F7F7 gray(247)
248: (248,248,248) #F8F8F8 gray(248)
249: (249,249,249) #F9F9F9 gray(249)
250: (250,250,250) #FAFAFA gray(250)
251: (251,251,251) #FBFBFB gray(251)
252: (252,252,252) #FCFCFC gray(252)
253: (253,253,253) #FDFDFD gray(253)
254: (254,254,254) #FEFEFE gray(254)
255: (255,255,255) #FFFFFF gray(255)
Rendering intent: Undefined
Gamma: 1
Background color: gray(255)
Border color: gray(223)
Matte color: gray(189)
Transparent color: gray(0)
Interlace: None
Intensity: Rec709Luminance
Compose: Over
Page geometry: 70x46+0+0
Dispose: Undefined
Iterations: 0
Compression: Zip
Orientation: Undefined
Properties:
date:create: 2013-10-15T09:49:07-07:00
date:modify: 2013-10-15T09:49:07-07:00
png:bKGD: chunk was found (see Background color, above)
png:gAMA: gamma=1 (See Gamma, above)
png:IHDR.bit-depth-orig: 8
png:IHDR.bit_depth: 8
png:IHDR.color-type-orig: 0
png:IHDR.color_type: 0 (Grayscale)
png:IHDR.interlace_method: 0 (Not interlaced)
png:IHDR.width,height: 70, 46
png:text: 2 tEXt/zTXt/iTXt chunks were found
signature: 6c40361a5da66526ad84d455db2743f96ce3d551608fc16d9f7ef75030e83eac
Artifacts:
filename: rose_luminance_1.png
verbose: true
Tainted: True
Filesize: 1.88KB
Number pixels: 3.22K
Pixels per second: 3.22EB
User time: 0.010u
Elapsed time: 0:01.000
Version: ImageMagick 6.8.7-1 2013-10-08 Q16 http://www.imagemagick.org
Code: Select all
Image: rose_luminance_2.png
Geometry: 70x46+0+0
Page geometry: 70x46+0+0
Class: PseudoClass
Colorspace: Gray
Type: Grayscale
Depth: 8/1-bit
Alpha: False
Channels: gray
Rendering intent: Undefined
Gamma: 1
Colors: 200
Gray:
min: 5 (0.0196078)
max: 255 (1)
mean: 49.9761 (0.195985)
standard deviation: 53.9087 (0.211407)
I'm not just looking for a method to perform the conversion, but a colorspace that would tag the image internally (and at least in miff) as to what kind of grayscale data your image represents. If -colorspace rec709luminance would actually set a colorspace called rec709luminance (not just "gray"), that would be a step in the right direction.fmw42 wrote:I suppose IM could have -colorspace rec709luminance, but that is the same as -grayscale rec709luminance. At least that was the way it was supposed to be apart from a recent bug that changed its behavior and which in principle should be fixed in 6.8.7.1 when it is released.