One of the moderators on our Inkscape G+ feed is blocking comments and slinging insults

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Re: Setting pHYs dpi in Inkscape

Marc Jeanmougin
> Is there a viewer which allows us to see the dpi settings (pixels per
> unit) of a png?
$ identify -verbose file.png | grep pHYs

> Is it set to something specific based on the user-entered dpi resolution?
>
Yes, except if overwritten by user-entered value in "pHYs dpi" box
(committed Sep 25, 2017) in "Advanced" settings of "Export PNG" dialog.

$ identify -verbose rect10.png | grep pHYs
    png:pHYs: x_res=3779, y_res=3779, units=1
=> (in pixels per meter, divide by 39,3701) => 96 ppi

$ identify -verbose rect10_72.png | grep pHYs
    png:pHYs: x_res=2834, y_res=2834, units=1
=> 72 ppi



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Re: Setting pHYs dpi in Inkscape

alvinpenner
In reply to this post by C R
on Windows I use exiftool. For a png saved at 300 dpi it gives me the
following info:
the resolution is reported as 11811 dots per meter, which is close to 300
dpi.

C:\Odds_and_Ends>exiftool \windows\temp\bitmap300.png
ExifTool Version Number         : 10.31
File Name                       : bitmap300.png
Directory                       : /windows/temp
File Size                       : 36 kB
File Modification Date/Time     : 2018:09:19 18:51:49-04:00
File Access Date/Time           : 2018:09:19 18:51:48-04:00
File Creation Date/Time         : 2018:09:19 18:51:44-04:00
File Permissions                : rw-rw-rw-
File Type                       : PNG
File Type Extension             : png
MIME Type                       : image/png
Image Width                     : 2480
Image Height                    : 3508
Bit Depth                       : 8
Color Type                      : RGB with Alpha
Compression                     : Deflate/Inflate
Filter                          : Adaptive
Interlace                       : Noninterlaced
Significant Bits                : 8 8 8 8
Pixels Per Unit X               : 11811
Pixels Per Unit Y               : 11811
Pixel Units                     : meters
Software                        : www.inkscape.org
Image Size                      : 2480x3508
Megapixels                      : 8.7



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Re: One of the moderators on our Inkscape G+ feed is blocking comments and slinging insults

Aditya Sher
In reply to this post by C R
Talking about printing is there any RG. To CMYK filter mode for inkscape? That will help convert RGB vectors to CMYK.

On Thu, Sep 20, 2018, 2:55 PM C R <[hidden email]> wrote:
Cool thanks for the good info. And yes, that's my experience too regarding printing of pngs.
I usually will wrap them in a pdf just to be sure the sizing is unambiguous, but some web printing companies will only accept jpeg or png files.

Maybe I'll call the video "DPI and the power of the PNG".

Can you provide some links to the information you've given here so I can include them in the sources for people to check out? (Cuts down trolling by "experts")

Thanks again for your help!


On Thu, Sep 20, 2018 at 7:32 AM Andrea Bogazzi <[hidden email]> wrote:
They surprisingly read it, almost all of them, or at least all the basic software of the OS from which people open the image and can quickly look at it.
PNG is an underrated format, is not well received from print companies, but things started to change since is what you get by default from web applications, and the only lossless.

They do convert in the nearest dpi value, even if the tag sets to some integer in dot per meter and then it becomes 299.9923 dot per inch. They will just print at 300.

Regarding the specs, no one will support the non square pixels that i know of, and by default you will always find 1, also no one will easily support different resolution per axis.

I did not follow the thread, are we missing png dpi support in inkscape?


Il giorno gio 20 set 2018 alle ore 08:20 C R <[hidden email]> ha scritto:
Nice! Excellent information.

So does Inkscape ever set a value for these or is it always 0 (unknown unit?)

Not that it really matters all that much... Any print company worth anything will know that a raster file of pixel dimensions 2480 pixels x 3508 pixels is A4 @ 300dpi (no bleed)

Yes, I've encountered printers who didn't, but it's pretty basic stuff, so I tend to avoid companies that can't get DPI right. :)

It's generally advisable to send a pdf, which includes the relevant size information, since it properly stores all that stuff, but imho, there's nothing wrong with popping out a png at the proper pixel dimensions and saying "I'd like this printed at A4 300 DPI". That should be more than enough information for any printer to get it the right size.

It's been on my to-do list for a while to make a video on DPI. 
It's quite astonishing how many designers (and printers) just don't understand it.

Thanks for the info. It would be a good idea to make use of the png unit specifier, however I don't know how many pieces of software will read the value and use it, even if we include it.

 -C

On Thu, Sep 20, 2018 at 1:36 AM ian_bruce--- via Inkscape-devel <[hidden email]> wrote:
On Wed, 19 Sep 2018 21:44:56 +0200
Andrea Bogazzi <[hidden email]> wrote:

> Just wanted to add the maybe non usefull information, but nice to
> know, that pngs are weirdly in DOT per METER. I think they are the
> only graphic format to do so.
>
> Being the conversion between meter and inch not an integer, you cannot
> have either 96 or 300 or 600dpi, but some float number in the nearby.

Here's the relevant part of the actual PNG specification, in case
somebody wants to quote it to the fool with 30 years experience
("Dunning-Kruger effect", haha).

https://www.w3.org/TR/PNG/#11pHYs

    The pHYs chunk specifies the intended pixel size or aspect ratio for
    display of the image. It contains:

    Pixels per unit, X axis    4 bytes (PNG unsigned integer)
    Pixels per unit, Y axis    4 bytes (PNG unsigned integer)
    Unit specifier             1 byte

    The following values are defined for the unit specifier:

    0    unit is unknown
    1    unit is the metre

    When the unit specifier is 0, the pHYs chunk defines pixel aspect
    ratio only; the actual size of the pixels remains unspecified.

    If the pHYs chunk is not present, pixels are assumed to be square,
    and the physical size of each pixel is unspecified.

There's obviously nothing that stops you from assuming that the
"unknown" unit is actually inches, or anything else, and setting the
pixels/unit values accordingly.

Maybe the Inkscape interface could be adjusted to allow the PNG output
resolution to be specified in dots/cm as well as dots/inch, and set the
unit specifier to 1 or 0, accordingly.


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Re: One of the moderators on our Inkscape G+ feed is blocking comments and slinging insults

C R
If you use linux, there's a command-line tool called ghostscript which will convert your pdf contents to CMYK.

just rename your pdf to "in.pdf" and run this command:

gs -o out.pdf -sDEVICE=pdfwrite -dUseCIEColor -sProcessColorModel=DeviceCMYK -sColorConversionStrategy=CMYK -dEncodeColorImages=false -sColorConversionStrategyForImages=CMYK in.pdf

This will make a pdf called out.pdf which will be CMYK

Note: Most printers have no problems converting your RGB pdf to CMYK, so you could always just let them do it. This will allow them to use their printer's own colour profile for a better match to your original file.

Hope it helps. :)
-C

On Thu, Sep 20, 2018 at 1:53 PM Aditya Sher <[hidden email]> wrote:
Talking about printing is there any RG. To CMYK filter mode for inkscape? That will help convert RGB vectors to CMYK.

On Thu, Sep 20, 2018, 2:55 PM C R <[hidden email]> wrote:
Cool thanks for the good info. And yes, that's my experience too regarding printing of pngs.
I usually will wrap them in a pdf just to be sure the sizing is unambiguous, but some web printing companies will only accept jpeg or png files.

Maybe I'll call the video "DPI and the power of the PNG".

Can you provide some links to the information you've given here so I can include them in the sources for people to check out? (Cuts down trolling by "experts")

Thanks again for your help!


On Thu, Sep 20, 2018 at 7:32 AM Andrea Bogazzi <[hidden email]> wrote:
They surprisingly read it, almost all of them, or at least all the basic software of the OS from which people open the image and can quickly look at it.
PNG is an underrated format, is not well received from print companies, but things started to change since is what you get by default from web applications, and the only lossless.

They do convert in the nearest dpi value, even if the tag sets to some integer in dot per meter and then it becomes 299.9923 dot per inch. They will just print at 300.

Regarding the specs, no one will support the non square pixels that i know of, and by default you will always find 1, also no one will easily support different resolution per axis.

I did not follow the thread, are we missing png dpi support in inkscape?


Il giorno gio 20 set 2018 alle ore 08:20 C R <[hidden email]> ha scritto:
Nice! Excellent information.

So does Inkscape ever set a value for these or is it always 0 (unknown unit?)

Not that it really matters all that much... Any print company worth anything will know that a raster file of pixel dimensions 2480 pixels x 3508 pixels is A4 @ 300dpi (no bleed)

Yes, I've encountered printers who didn't, but it's pretty basic stuff, so I tend to avoid companies that can't get DPI right. :)

It's generally advisable to send a pdf, which includes the relevant size information, since it properly stores all that stuff, but imho, there's nothing wrong with popping out a png at the proper pixel dimensions and saying "I'd like this printed at A4 300 DPI". That should be more than enough information for any printer to get it the right size.

It's been on my to-do list for a while to make a video on DPI. 
It's quite astonishing how many designers (and printers) just don't understand it.

Thanks for the info. It would be a good idea to make use of the png unit specifier, however I don't know how many pieces of software will read the value and use it, even if we include it.

 -C

On Thu, Sep 20, 2018 at 1:36 AM ian_bruce--- via Inkscape-devel <[hidden email]> wrote:
On Wed, 19 Sep 2018 21:44:56 +0200
Andrea Bogazzi <[hidden email]> wrote:

> Just wanted to add the maybe non usefull information, but nice to
> know, that pngs are weirdly in DOT per METER. I think they are the
> only graphic format to do so.
>
> Being the conversion between meter and inch not an integer, you cannot
> have either 96 or 300 or 600dpi, but some float number in the nearby.

Here's the relevant part of the actual PNG specification, in case
somebody wants to quote it to the fool with 30 years experience
("Dunning-Kruger effect", haha).

https://www.w3.org/TR/PNG/#11pHYs

    The pHYs chunk specifies the intended pixel size or aspect ratio for
    display of the image. It contains:

    Pixels per unit, X axis    4 bytes (PNG unsigned integer)
    Pixels per unit, Y axis    4 bytes (PNG unsigned integer)
    Unit specifier             1 byte

    The following values are defined for the unit specifier:

    0    unit is unknown
    1    unit is the metre

    When the unit specifier is 0, the pHYs chunk defines pixel aspect
    ratio only; the actual size of the pixels remains unspecified.

    If the pHYs chunk is not present, pixels are assumed to be square,
    and the physical size of each pixel is unspecified.

There's obviously nothing that stops you from assuming that the
"unknown" unit is actually inches, or anything else, and setting the
pixels/unit values accordingly.

Maybe the Inkscape interface could be adjusted to allow the PNG output
resolution to be specified in dots/cm as well as dots/inch, and set the
unit specifier to 1 or 0, accordingly.


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Re: One of the moderators on our Inkscape G+ feed is blocking comments and slinging insults

Aditya Sher
Got it, thankyou so much CR :) 

On Thu, Sep 20, 2018, 6:29 PM C R <[hidden email]> wrote:
If you use linux, there's a command-line tool called ghostscript which will convert your pdf contents to CMYK.

just rename your pdf to "in.pdf" and run this command:

gs -o out.pdf -sDEVICE=pdfwrite -dUseCIEColor -sProcessColorModel=DeviceCMYK -sColorConversionStrategy=CMYK -dEncodeColorImages=false -sColorConversionStrategyForImages=CMYK in.pdf

This will make a pdf called out.pdf which will be CMYK

Note: Most printers have no problems converting your RGB pdf to CMYK, so you could always just let them do it. This will allow them to use their printer's own colour profile for a better match to your original file.

Hope it helps. :)
-C

On Thu, Sep 20, 2018 at 1:53 PM Aditya Sher <[hidden email]> wrote:
Talking about printing is there any RG. To CMYK filter mode for inkscape? That will help convert RGB vectors to CMYK.

On Thu, Sep 20, 2018, 2:55 PM C R <[hidden email]> wrote:
Cool thanks for the good info. And yes, that's my experience too regarding printing of pngs.
I usually will wrap them in a pdf just to be sure the sizing is unambiguous, but some web printing companies will only accept jpeg or png files.

Maybe I'll call the video "DPI and the power of the PNG".

Can you provide some links to the information you've given here so I can include them in the sources for people to check out? (Cuts down trolling by "experts")

Thanks again for your help!


On Thu, Sep 20, 2018 at 7:32 AM Andrea Bogazzi <[hidden email]> wrote:
They surprisingly read it, almost all of them, or at least all the basic software of the OS from which people open the image and can quickly look at it.
PNG is an underrated format, is not well received from print companies, but things started to change since is what you get by default from web applications, and the only lossless.

They do convert in the nearest dpi value, even if the tag sets to some integer in dot per meter and then it becomes 299.9923 dot per inch. They will just print at 300.

Regarding the specs, no one will support the non square pixels that i know of, and by default you will always find 1, also no one will easily support different resolution per axis.

I did not follow the thread, are we missing png dpi support in inkscape?


Il giorno gio 20 set 2018 alle ore 08:20 C R <[hidden email]> ha scritto:
Nice! Excellent information.

So does Inkscape ever set a value for these or is it always 0 (unknown unit?)

Not that it really matters all that much... Any print company worth anything will know that a raster file of pixel dimensions 2480 pixels x 3508 pixels is A4 @ 300dpi (no bleed)

Yes, I've encountered printers who didn't, but it's pretty basic stuff, so I tend to avoid companies that can't get DPI right. :)

It's generally advisable to send a pdf, which includes the relevant size information, since it properly stores all that stuff, but imho, there's nothing wrong with popping out a png at the proper pixel dimensions and saying "I'd like this printed at A4 300 DPI". That should be more than enough information for any printer to get it the right size.

It's been on my to-do list for a while to make a video on DPI. 
It's quite astonishing how many designers (and printers) just don't understand it.

Thanks for the info. It would be a good idea to make use of the png unit specifier, however I don't know how many pieces of software will read the value and use it, even if we include it.

 -C

On Thu, Sep 20, 2018 at 1:36 AM ian_bruce--- via Inkscape-devel <[hidden email]> wrote:
On Wed, 19 Sep 2018 21:44:56 +0200
Andrea Bogazzi <[hidden email]> wrote:

> Just wanted to add the maybe non usefull information, but nice to
> know, that pngs are weirdly in DOT per METER. I think they are the
> only graphic format to do so.
>
> Being the conversion between meter and inch not an integer, you cannot
> have either 96 or 300 or 600dpi, but some float number in the nearby.

Here's the relevant part of the actual PNG specification, in case
somebody wants to quote it to the fool with 30 years experience
("Dunning-Kruger effect", haha).

https://www.w3.org/TR/PNG/#11pHYs

    The pHYs chunk specifies the intended pixel size or aspect ratio for
    display of the image. It contains:

    Pixels per unit, X axis    4 bytes (PNG unsigned integer)
    Pixels per unit, Y axis    4 bytes (PNG unsigned integer)
    Unit specifier             1 byte

    The following values are defined for the unit specifier:

    0    unit is unknown
    1    unit is the metre

    When the unit specifier is 0, the pHYs chunk defines pixel aspect
    ratio only; the actual size of the pixels remains unspecified.

    If the pHYs chunk is not present, pixels are assumed to be square,
    and the physical size of each pixel is unspecified.

There's obviously nothing that stops you from assuming that the
"unknown" unit is actually inches, or anything else, and setting the
pixels/unit values accordingly.

Maybe the Inkscape interface could be adjusted to allow the PNG output
resolution to be specified in dots/cm as well as dots/inch, and set the
unit specifier to 1 or 0, accordingly.


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Re: One of the moderators on our Inkscape G+ feed is blocking comments and slinging insults

C R
surething. :)
-C

On Thu, Sep 20, 2018 at 2:02 PM Aditya Sher <[hidden email]> wrote:
Got it, thankyou so much CR :) 

On Thu, Sep 20, 2018, 6:29 PM C R <[hidden email]> wrote:
If you use linux, there's a command-line tool called ghostscript which will convert your pdf contents to CMYK.

just rename your pdf to "in.pdf" and run this command:

gs -o out.pdf -sDEVICE=pdfwrite -dUseCIEColor -sProcessColorModel=DeviceCMYK -sColorConversionStrategy=CMYK -dEncodeColorImages=false -sColorConversionStrategyForImages=CMYK in.pdf

This will make a pdf called out.pdf which will be CMYK

Note: Most printers have no problems converting your RGB pdf to CMYK, so you could always just let them do it. This will allow them to use their printer's own colour profile for a better match to your original file.

Hope it helps. :)
-C

On Thu, Sep 20, 2018 at 1:53 PM Aditya Sher <[hidden email]> wrote:
Talking about printing is there any RG. To CMYK filter mode for inkscape? That will help convert RGB vectors to CMYK.

On Thu, Sep 20, 2018, 2:55 PM C R <[hidden email]> wrote:
Cool thanks for the good info. And yes, that's my experience too regarding printing of pngs.
I usually will wrap them in a pdf just to be sure the sizing is unambiguous, but some web printing companies will only accept jpeg or png files.

Maybe I'll call the video "DPI and the power of the PNG".

Can you provide some links to the information you've given here so I can include them in the sources for people to check out? (Cuts down trolling by "experts")

Thanks again for your help!


On Thu, Sep 20, 2018 at 7:32 AM Andrea Bogazzi <[hidden email]> wrote:
They surprisingly read it, almost all of them, or at least all the basic software of the OS from which people open the image and can quickly look at it.
PNG is an underrated format, is not well received from print companies, but things started to change since is what you get by default from web applications, and the only lossless.

They do convert in the nearest dpi value, even if the tag sets to some integer in dot per meter and then it becomes 299.9923 dot per inch. They will just print at 300.

Regarding the specs, no one will support the non square pixels that i know of, and by default you will always find 1, also no one will easily support different resolution per axis.

I did not follow the thread, are we missing png dpi support in inkscape?


Il giorno gio 20 set 2018 alle ore 08:20 C R <[hidden email]> ha scritto:
Nice! Excellent information.

So does Inkscape ever set a value for these or is it always 0 (unknown unit?)

Not that it really matters all that much... Any print company worth anything will know that a raster file of pixel dimensions 2480 pixels x 3508 pixels is A4 @ 300dpi (no bleed)

Yes, I've encountered printers who didn't, but it's pretty basic stuff, so I tend to avoid companies that can't get DPI right. :)

It's generally advisable to send a pdf, which includes the relevant size information, since it properly stores all that stuff, but imho, there's nothing wrong with popping out a png at the proper pixel dimensions and saying "I'd like this printed at A4 300 DPI". That should be more than enough information for any printer to get it the right size.

It's been on my to-do list for a while to make a video on DPI. 
It's quite astonishing how many designers (and printers) just don't understand it.

Thanks for the info. It would be a good idea to make use of the png unit specifier, however I don't know how many pieces of software will read the value and use it, even if we include it.

 -C

On Thu, Sep 20, 2018 at 1:36 AM ian_bruce--- via Inkscape-devel <[hidden email]> wrote:
On Wed, 19 Sep 2018 21:44:56 +0200
Andrea Bogazzi <[hidden email]> wrote:

> Just wanted to add the maybe non usefull information, but nice to
> know, that pngs are weirdly in DOT per METER. I think they are the
> only graphic format to do so.
>
> Being the conversion between meter and inch not an integer, you cannot
> have either 96 or 300 or 600dpi, but some float number in the nearby.

Here's the relevant part of the actual PNG specification, in case
somebody wants to quote it to the fool with 30 years experience
("Dunning-Kruger effect", haha).

https://www.w3.org/TR/PNG/#11pHYs

    The pHYs chunk specifies the intended pixel size or aspect ratio for
    display of the image. It contains:

    Pixels per unit, X axis    4 bytes (PNG unsigned integer)
    Pixels per unit, Y axis    4 bytes (PNG unsigned integer)
    Unit specifier             1 byte

    The following values are defined for the unit specifier:

    0    unit is unknown
    1    unit is the metre

    When the unit specifier is 0, the pHYs chunk defines pixel aspect
    ratio only; the actual size of the pixels remains unspecified.

    If the pHYs chunk is not present, pixels are assumed to be square,
    and the physical size of each pixel is unspecified.

There's obviously nothing that stops you from assuming that the
"unknown" unit is actually inches, or anything else, and setting the
pixels/unit values accordingly.

Maybe the Inkscape interface could be adjusted to allow the PNG output
resolution to be specified in dots/cm as well as dots/inch, and set the
unit specifier to 1 or 0, accordingly.


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