failed to resize a transparent png keeping bitdepth fixed

[amirian]

Hi, I'm using IM-7.0.10-13-Q16-x64 to resize a 196KB grayscale png image with transparent background (also made by IM long ago) from 1024x1656 into 1260x2038 pixels. I tried following parameters but gor no correct output: the file gets too large and for PNG00 format the transparency is broken to black. How can I fix this without increasing the bit depth and file size?
convert input.png -resize 1260x2038 1.png Output depth:32, size:1.5MB
convert input.png -resize 1260x2038 -depth 4 2.png Output depth:32, size:830KB
convert input.png -resize 1260x2038 -depth 4 PNG00:3.png Output depth:8, size:655KB (Transparency broken, with this warning: "convert: Cannot write image with defined png:bit-depth or png:color-type. `3.png' @ warning/png.c/MagickPNGWarningHandler/1748.")
convert input.png -resize 1260x2038 -depth 2 4.png Output depth:32, size:430KB
convert input.png -resize 1260x2038 -depth 2 PNG00:5.png Output depth:4, size:310KB (Transparency broken)

[snibgo]

For v7, I suggest you use "magick", not "convert" (and not "magick convert").

Please show input.png. If it is confidential, please show the complete text output from:
magick input.png -verbose info:

[amirian]

changing to "magick" didn't affect the output. Is it necessary to show the content of the image?
magick input.png -verbose info
input.png=>info PNG 1024x1656 1024x1656+0+0 8-bit sRGB 201559B 1.000u 0:00.435
In windows file properties, it is reported as 4 bit depth

[snibgo]

Please try again, this time with a colon at the end of info:

[amirian]

Image:
Filename: input.png
Format: PNG (Portable Network Graphics)
Mime type: image/png
Class: DirectClass
Geometry: 1024x1656+0+0
Units: Undefined
Colorspace: sRGB
Type: GrayscaleAlpha
Base type: Undefined
Endianness: Undefined
Depth: 8-bit
Channel depth:
Red: 8-bit
Green: 8-bit
Blue: 8-bit
Alpha: 1-bit
Channel statistics:
Pixels: 1695744
Red:
min: 0 (0)
max: 238 (0.933333)
mean: 45.2599 (0.17749)
standard deviation: 89.8903 (0.352511)
kurtosis: 0.297608
skewness: 1.50363
entropy: 0.391504
Green:
min: 0 (0)
max: 238 (0.933333)
mean: 45.2599 (0.17749)
standard deviation: 89.8903 (0.352511)
kurtosis: 0.297608
skewness: 1.50363
entropy: 0.391504
Blue:
min: 0 (0)
max: 238 (0.933333)
mean: 45.2599 (0.17749)
standard deviation: 89.8903 (0.352511)
kurtosis: 0.297608
skewness: 1.50363
entropy: 0.391504
Alpha:
min: 0 (0)
max: 255 (1)
mean: 80.9071 (0.317283)
standard deviation: 118.682 (0.465419)
kurtosis: -1.3835
skewness: 0.785174
entropy: 0.901402
Image statistics:
Overall:
min: 0 (0)
max: 255 (1)
mean: 54.1717 (0.212438)
standard deviation: 97.0882 (0.380738)
kurtosis: -0.244904
skewness: 1.30708
entropy: 0.518978
Alpha: none #00000000
Colors: 8
Histogram:
1.15771e+006: (0,0,0,0) #00000000 none
189938: (0,0,0,255) #000000FF black
5760: (50,50,50,255) #323232FF srgba(50,50,50,1)
189: (68,68,68,255) #444444FF srgba(68,68,68,1)
11082: (187,187,187,255) #BBBBBBFF srgba(187,187,187,1)
82180: (204,204,204,255) #CCCCCCFF grey80
95438: (221,221,221,255) #DDDDDDFF srgba(221,221,221,1)
153443: (238,238,238,255) #EEEEEEFF srgba(238,238,238,1)
Rendering intent: Perceptual
Gamma: 0.454545
Chromaticity:
red primary: (0.64,0.33)
green primary: (0.3,0.6)
blue primary: (0.15,0.06)
white point: (0.3127,0.329)
Matte color: grey74
Background color: white
Border color: srgb(223,223,223)
Transparent color: none
Interlace: None
Intensity: Undefined
Compose: Over
Page geometry: 1024x1656+0+0
Dispose: Undefined
Iterations: 0
Compression: Zip
Orientation: Undefined
Convex hull: 264,23 760,23 1004,74 1005,75 1013,307 1013,1344 1007,1550 1004,1559 983,1582 982,1583 883,1625 762,1632 263,1632 11,1611 10,1610 10,290 15,70 17,36 155,26 264,23
Minimum bounding box: 1013,23 1013,1632 10,1632 10,23
Properties:
date:create: 2020-05-18T13:57:03+00:00
date:modify: 2011-10-12T18:40:36+00:00
minimum-bounding-box:_p: 264,23
minimum-bounding-box:_q: 760,23
minimum-bounding-box:_v: 762,1632
minimum-bounding-box:angle: 0
minimum-bounding-box:area: 1.61383e+006
minimum-bounding-box:height: 1003
minimum-bounding-box:unrotate: -0
minimum-bounding-box:width: 1609
png:IHDR.bit-depth-orig: 4
png:IHDR.bit_depth: 4
png:IHDR.color-type-orig: 3
png:IHDR.color_type: 3 (Indexed)
png:IHDR.interlace_method: 0 (Not interlaced)
png:IHDR.width,height: 1024, 1656
png:PLTE.number_colors: 8
png:sRGB: intent=0 (Perceptual Intent)
png:tRNS: chunk was found
signature: 649ee651c26c1cb42d0b1658348611df37cd0f00b8a2e16a3d68511d7b8c6f96
Tainted: False
Filesize: 201559B
Number pixels: 1.69574M
Pixels per second: 15.623MP
User time: 0.219u
Elapsed time: 0:01.108
Version: ImageMagick 7.0.10-13 Q16 x64 2020-05-17 http://www.imagemagick.org

[amirian]

No solution yet?

[fmw42]

Can you post an example image that fails?

[amirian]

this is the info:
magick input.png -verbose info:
Image:
Filename: input.png
Format: PNG (Portable Network Graphics)
Mime type: image/png
Class: DirectClass
Geometry: 1024x1656+0+0
Units: Undefined
Colorspace: sRGB
Type: GrayscaleAlpha
Base type: Undefined
Endianness: Undefined
Depth: 8/4-bit
Channel depth:
Red: 4-bit
Green: 4-bit
Blue: 4-bit
Alpha: 1-bit
Channel statistics:
Pixels: 1695744
Red:
min: 0 (0)
max: 238 (0.933333)
mean: 21.4482 (0.0841105)
standard deviation: 65.7974 (0.258029)
kurtosis: 5.90919
skewness: 2.79778
entropy: 0.235651
Green:
min: 0 (0)
max: 238 (0.933333)
mean: 21.4482 (0.0841105)
standard deviation: 65.7974 (0.258029)
kurtosis: 5.90919
skewness: 2.79778
entropy: 0.235651
Blue:
min: 0 (0)
max: 238 (0.933333)
mean: 21.4482 (0.0841105)
standard deviation: 65.7974 (0.258029)
kurtosis: 5.90919
skewness: 2.79778
entropy: 0.235651
Alpha:
min: 0 (0)
max: 255 (1)
mean: 40.0797 (0.157175)
standard deviation: 92.8113 (0.363966)
kurtosis: 1.54881
skewness: 1.88383
entropy: 0.627509
Image statistics:
Overall:
min: 0 (0)
max: 255 (1)
mean: 26.1061 (0.102377)
standard deviation: 72.5509 (0.284513)
kurtosis: 4.4478
skewness: 2.52374
entropy: 0.333615
Alpha: none #00000000
Colors: 8
Histogram:
1.42922e+006: (0,0,0,0) #00000000 none
95491: (0,0,0,255) #000000FF black
11433: (51,51,51,255) #333333FF grey20
1381: (68,68,68,255) #444444FF srgba(68,68,68,1)
3141: (187,187,187,255) #BBBBBBFF srgba(187,187,187,1)
32503: (204,204,204,255) #CCCCCCFF grey80
41082: (221,221,221,255) #DDDDDDFF srgba(221,221,221,1)
81498: (238,238,238,255) #EEEEEEFF srgba(238,238,238,1)
Rendering intent: Perceptual
Gamma: 0.454545
Chromaticity:
red primary: (0.64,0.33)
green primary: (0.3,0.6)
blue primary: (0.15,0.06)
white point: (0.3127,0.329)
Matte color: grey74
Background color: white
Border color: srgb(223,223,223)
Transparent color: none
Interlace: None
Intensity: Undefined
Compose: Over
Page geometry: 1024x1656+0+0
Dispose: Undefined
Iterations: 0
Compression: Zip
Orientation: Undefined
Convex hull: 507,7 521,8 522,9 814,360 954,530 1023,718 1023,939 975,1138 971,1144 522,1653 507,1655 505,1655 3,1269 2,1268 1,922 1,921 4,729 5,714 80,524 209,352 506,8 507,7
Minimum bounding box: 512.406,0.580213 1341,716 496,1695 -332,980
Properties:
date:create: 2020-05-20T10:51:15+00:00
date:modify: 2011-10-12T19:21:40+00:00
minimum-bounding-box:_p: 209,352
minimum-bounding-box:_q: 506,8
minimum-bounding-box:_v: 971,1144
minimum-bounding-box:angle: 40.8078
minimum-bounding-box:area: 1.41499e+006
minimum-bounding-box:height: 1292.99
minimum-bounding-box:unrotate: -40.8078
minimum-bounding-box:width: 1094.35
png:IHDR.bit-depth-orig: 4
png:IHDR.bit_depth: 4
png:IHDR.color-type-orig: 3
png:IHDR.color_type: 3 (Indexed)
png:IHDR.interlace_method: 0 (Not interlaced)
png:IHDR.width,height: 1024, 1656
png:PLTE.number_colors: 8
png:sRGB: intent=0 (Perceptual Intent)
png:tRNS: chunk was found
signature: ba1b3588994288366b6f9344b80fb66e69fc2176ff766c32eea75092120fb4b3
Tainted: False
Filesize: 113310B
Number pixels: 1.69574M
Pixels per second: 18.2991MP
User time: 0.172u
Elapsed time: 0:01.092
Version: ImageMagick 7.0.10-13 Q16 x64 2020-05-17 http://www.imagemagick.org

[snibgo]

@amirian: your input has eight colours. Resizing will greatly increase the number of colours, including anti-aliasing of alpha, so the result won't compress so easily, so the output file will be large. You could use "-sample" instead of "-resize", but the result will be fairly horrible.

I don't know what is causing your broken transparency problem. Why do you want "png00:"? This seems to be a bad idea.

You want to resize an image that has already been heavily processed. It would be better to get a high-quality version of that image, and process that to your needs.

[amirian]

Thanks for reply. I first tried to re-generate 1260x2038 from scratch, but the old scripts needs a large change to fit with the current IM version. the -sample really lowers the quality. I use png00 only for keeping the bit depth! So, how can I fit the output large png into 4-bit depth without that?

[snibgo]

How can you resize that heavily processed image, AND keep reasonable qualiy, AND store it in 4-bits per pixel? I haven't tried all possible combinations (eg with "-colors 16" and "-depth 4"), but I don't think that is possible.

I suggest you start with a better quality input.

[amirian]

I don't think that is the problem, because even with -sample I get a 32 bit output, also even with -colors 16 and -depth 4!

[fmw42]

This works OK for me on IM 7.0.10.13 Q16 Mac OSX.

magick pattern.png -resize 1260x2038 -depth 4 x.png

[fmw42]

Try

magick pattern.png -strip -resize 1024x1656 -depth 4 -type grayscalealpha -define png:bit-depth=4 PNG8:x.png

Remaining file size differences are likely from the PNG compression. You can play with that if you want. see

https://imagemagick.org/Usage/formats/#png_write
https://imagemagick.org/script/command-line-options.php#quality

[amirian]

That works for the same pixel size, but for enlarging to 1260x2038, I get the following error:
magick: Invalid palette length `x2.png' @ error/png.c/MagickPNGErrorHandler/1715.

[fmw42]

I get the same error message. One of the IM developers will need to look into this.

[snibgo]

On the error message, see https://www.imagemagick.org/script/command-line-options.php#define png:bit-depth . To fix this, use "-colors 16".

[amirian]

That all works, thank you.