Print colours

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Iain Hallam - 23 Jul 2003 13:12 GMT

Hi.

I'm printing from various programs under Win98SE where I have a rectangle of a
colour (rgb 175,232,255) overlaid with a PNG whose background is the same. When
I print using the high resolution mode on a Canon BJC3000, the rectangle always
comes out darker than the background of the PNG - Word, Publisher, PagePlus all
do the same.

I could use an alpha layer in the PNG to show the main picture (antialiased
white outlines) with no background, but Word at least seems to lose all alpha
channels in the import process.

Any suggestions?

Thanks,

Iain Hallam.

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C.D.Kuder - 23 Jul 2003 18:35 GMT

The higher resolution mode is obviously putting more ink on the paper,
perhaps way to much.
Blue is a color that often prints darker than desired. Is the correct paper
selected?
The printer drivers generally have manual color adjustment available. You
may need to decrease the color intensity.

Paper is a big variable. One brand and type will work well, another may
allow the ink to pool on the surface.

There is a lot of stuff behind the printer driver and printer that is not
obvious.
One is that a color that ranges from an RGB value of 0 to 255 will usually
not print with 255 shades.
The colors with values above 180 or so may all print the same, and 255 may
cause a wet printed page.
The printer driver is responsible for reducing this problem to a reasonable
level.

A simular issue can occur at the low end. 10-50 values may not be much
different, and may print much lighter or darker than you would expect.

> Hi.
>
[quoted text clipped - 13 lines]
>
> Iain Hallam.

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Iain Hallam - 24 Jul 2003 00:11 GMT

> The higher resolution mode is obviously putting more ink on the paper,
> perhaps way to much.
> Blue is a color that often prints darker than desired. Is the correct paper
> selected?
> The printer drivers generally have manual color adjustment available. You
> may need to decrease the color intensity.

It's not that the print is all too dark (although it may be, I haven't really
checked). The problem here is that an image containing 175,232,255 is coming out
a different colour than the rectangle next to it, also coloured 175,232,255. I
wouldn't mind too much if they were both off by the same amount. This happens
with all DTP programs I've tried - Word, PagePlus, OpenOffice Writer, Publisher.

- Iain.

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Glenn Randers-Pehrson - 25 Jul 2003 12:56 GMT

> > The higher resolution mode is obviously putting more ink on the paper,
> > perhaps way to much.
[quoted text clipped - 10 lines]
>
> - Iain.

Does your PNG file contain a gAMA chunk? MSIE and perhaps other Microsoft
products don't handle gAMA correctly. See if it helps to remove the
gAMA chunk and put in an sRGB chunk instead. You can use pngcrush to
do that:

pngcrush -n -v in.png (to see what chunks are in the file)
pngcrush -srgb 1 in.png temp.png (to add the sRGB chunk, also inserts
gAMA and cHRM chunks)
pngcrush -rem gama -rem chrm temp.png out.png (to remove gAMA and cHRM)

Get pngcrush (freeware) from pmt.sf.net

Glenn

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Iain Hallam - 28 Jul 2003 00:58 GMT

> Does your PNG file contain a gAMA chunk? MSIE and perhaps other Microsoft
> products don't handle gAMA correctly. See if it helps to remove the
> gAMA chunk and put in an sRGB chunk instead. You can use pngcrush to
> do that:
>
> Glenn

Thanks for the suggestion - I bypassed PNG and used a BMP with the same values,
no alpha. Same problem. The rectangle from Word was many shades darker than the
background of the image, despite both being set to 175,232,255.

I'm really at a loss to explain this other than being a printer driver fault -
it's a Canon BJC3000.

- Iain.

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