microsoft
Darkening when converting to BC7
PNG with:
Results by item ( 1) and mip ( 1)
Minimum - (0,000000 0,000000 0,000000 1,000000)
Average - (0,453539 0,328506 0,274346 1,000000)
Maximum - (1,000000 1,000000 1,000000 1,000000)
Variance - (10361,523438 7514,796875 3659,034424 0,000000)
Std Dev - (101,791565 86,687927 60,489952 0,000000)
Luminance - 1,000000 (maximum)
texconv -y -f BC7_UNORM -ft dds -m 1 image.png
DDS:
Results by item ( 1) and mip ( 1)
Minimum - (0,000000 0,000000 0,000000 0,984314)
Average - (0,265290 0,151262 0,089996 0,999930)
Maximum - (1,000000 1,000000 1,000000 1,000000)
Variance - (10718,610352 5891,852539 1872,661865 0,038926)
Std Dev - (103,530724 76,758400 43,274261 0,197297)
Luminance - 1,000000 (maximum)
Compression - BC7_UNORM
Total blocks - 8025
Mode 01 blocks - 3977
Mode 03 blocks - 2185
Mode 04 blocks - 549
Mode 05 blocks - 450
Mode 06 blocks - 832
Mode 07 blocks - 32
This seems like an issue related to SRGB vs. Linear. Is the BC7_UNORM content being rendered as SRGB or as Linear?
texconv -y -f BC7_UNORM -ft dds -m 1 -srgbo image.png
Results by item ( 1) and mip ( 1)
Minimum - (0,000000 0,000000 0,000000 0,984314)
Average - (0,453349 0,328474 0,274358 0,999889)
Maximum - (1,000000 1,000000 1,000000 1,000000)
Variance - (10363,500977 7532,208984 3677,713623 0,076049)
Std Dev - (101,801285 86,788300 60,644157 0,275769)
Luminance - 1,000000 (maximum)
Compression - BC7_UNORM
Total blocks - 8025
Mode 01 blocks - 5219
Mode 03 blocks - 1278
Mode 04 blocks - 761
Mode 05 blocks - 228
Mode 06 blocks - 470
Mode 07 blocks - 69
Why doesn't it detect the output format automatically? This is very inconvenient for batch processing. Some images become lighter with -srgbo.
Can you attach the image.png in question? You probably need to be using BC7_UNORM_SRGB as your output format.
texconv -y -f BC7_UNORM_SRGB -ft dds -m 1 image.png
Results by item ( 1) and mip ( 1)
Minimum - (0,000000 0,000000 0,000000 0,984314)
Average - (0,265700 0,151264 0,090136 0,999889)
Maximum - (1,000000 1,000000 1,000000 1,000000)
Variance - (10710,864258 5889,501953 1871,927856 0,076049)
Std Dev - (103,493309 76,743088 43,265781 0,275769)
Luminance - 1,000000 (maximum)
Compression - BC7_UNORM_SRGB
Total blocks - 8025
Mode 01 blocks - 5219
Mode 03 blocks - 1278
Mode 04 blocks - 761
Mode 05 blocks - 228
Mode 06 blocks - 470
Mode 07 blocks - 69
Declaring the sRGB format in image.png seems to correct the color in dds.
magick image.png -set colorspace sRGB image.png
texconv -y -f BC7_UNORM -ft dds -m 1 image.png
Results by item ( 1) and mip ( 1)
Minimum - (0,000000 0,000000 0,000000 0,984314)
Average - (0,460786 0,335521 0,280488 0,999896)
Maximum - (1,000000 1,000000 1,000000 1,000000)
Variance - (10343,784180 7622,896973 3820,479492 0,072577)
Std Dev - (101,704399 87,309204 61,810028 0,269401)
Luminance - 1,000000 (maximum)
Compression - BC7_UNORM
Total blocks - 8025
Mode 01 blocks - 5370
Mode 03 blocks - 1157
Mode 04 blocks - 850
Mode 05 blocks - 201
Mode 06 blocks - 381
Mode 07 blocks - 66
Images with such exif became darker:
ExifTool
ExifTool Version Number 12.85
Warning [minor] Trailer data after PNG IEND chunk
File
File Name image.png
Directory ...
File Size 6.5 MB
File Permissions -rw-rw-rw-
File Type PNG
File Type Extension png
MIME Type image/png
Composite
Image Size 2576x1816
Megapixels 4.7
ICC_Profile
Profile CMM Type Linotronic
Profile Version 2.1.0
Profile Class Display Device Profile
Color Space Data RGB
Profile Connection Space XYZ
Profile Date Time 1998:02:09 06:49:00
Profile File Signature acsp
Primary Platform Microsoft Corporation
CMM Flags Not Embedded, Independent
Device Manufacturer Hewlett-Packard
Device Model sRGB
Device Attributes Reflective, Glossy, Positive, Color
Rendering Intent Perceptual
Connection Space Illuminant 0.9642 1 0.82491
Profile Creator Hewlett-Packard
Profile ID 0
Profile Copyright Copyright (c) 1998 Hewlett-Packard Company
Profile Description sRGB IEC61966-2.1
Media White Point 0.95045 1 1.08905
Media Black Point 0 0 0
Red Matrix Column 0.43607 0.22249 0.01392
Green Matrix Column 0.38515 0.71687 0.09708
Blue Matrix Column 0.14307 0.06061 0.7141
Device Mfg Desc IEC http://www.iec.ch
Device Model Desc IEC 61966-2.1 Default RGB colour space - sRGB
Viewing Cond Desc Reference Viewing Condition in IEC61966-2.1
Viewing Cond Illuminant 19.6445 20.3718 16.8089
Viewing Cond Surround 3.92889 4.07439 3.36179
Viewing Cond Illuminant Type D50
Luminance 76.03647 80 87.12462
Measurement Observer CIE 1931
Measurement Backing 0 0 0
Measurement Geometry Unknown
Measurement Flare 0.999%
Measurement Illuminant D65
Technology Cathode Ray Tube Display
Red Tone Reproduction Curve (Binary data 2060 bytes, use -b option to extract)
Green Tone Reproduction Curve (Binary data 2060 bytes, use -b option to extract)
Blue Tone Reproduction Curve (Binary data 2060 bytes, use -b option to extract)
PNG
Image Width 2576
Image Height 1816
Bit Depth 8
Color Type RGB with Alpha
Compression Deflate/Inflate
Filter Adaptive
Interlace Noninterlaced
Gamma 2.2
Profile Name sRGB IEC61966-2.1
White Point X 0.3127
White Point Y 0.329
Red X 0.64
Red Y 0.33
Green X 0.3
Green Y 0.6
Blue X 0.15
Blue Y 0.06
Pixels Per Unit X 3780
Pixels Per Unit Y 3780
Pixel Units meters
After magick image.png -set colorspace sRGB image.png:
ExifTool ExifTool Version Number 12.85 Warning [minor] Text/EXIF chunk(s) found after PNG IDAT (may be ignored by some readers)
File
File Name image.png
Directory ...
File Size 5.7 MB
File Permissions -rw-rw-rw-
File Type PNG
File Type Extension png
MIME Type image/png
Composite
Image Size 2576x1816
Megapixels 4.7
PNG
Image Width 2576
Image Height 1816
Bit Depth 8
Color Type RGB with Alpha
Compression Deflate/Inflate
Filter Adaptive
Interlace Noninterlaced
White Point X 0.3127
White Point Y 0.329
Red X 0.64
Red Y 0.33
Green X 0.3
Green Y 0.6
Blue X 0.15
Blue Y 0.06
Background Color 255 255 255
Pixels Per Unit X 3779
Pixels Per Unit Y 3779
Pixel Units meters
It would seem then that you are using DXGI_FORMAT_BC7_UNORM and assuming that data is in linear RGB space, but when you read the PNG file it is missing the sRGB colorspace marker so it's not converting from sRGB to Linear.
Is that correct?