Brightness / contrast of PNGs

A

ArtWorker

I'm assembling user manuals from a bunch of extant "chapter" docs. These have
embedded screenshot images, many of which need to be updated. To cut down
file size I want to link the new ones to files. The current image files are
mostly PNGs with some BMPs. I've snagged some new screenshots, but the very
first PNG I linked in shows up with its contrast and brightness whacked. I
can tweak these options, but I'm having a hard time getting back to the
original on-screen settings. Whereas if I link to a GIF version of the same
image it shows up perfectly with no tweaking necessary. I would use GIfs
throughout but I will need to tweak some for size, and of course that will
make them look cruddy at any other resolution than 100%. Is there some sort
of import option for the PNGs that I am missing? All the extant ones are set
at 50% / 50% for brightness and contrast, but the new one sure didn't look
right that way.

Anyone have suggestions for me?
 
A

ArtWorker

I've been poking around this NG for info but haven't found anything directly
relevant to my issue. In a way it doesn't matter -- I can replace all the old
full-size shots with unindexed BMP versions, linked-to-file; that way I can
resize them any way I want and maintain color integrity. For the smaller ones
I can use GIFs. Still, I'd like to know what is happening.
 
A

ArtWorker

I suppose I should mention that I'm using Word 2002 on an HP box with Windows
2000 Pro.
 
B

Bob Buckland ?:-\)

Hi ArtWorker,

It's not something that I've seen often.

There are several possibilities that come to mind
including those related to gamma correction available
in one app not stored in the actual graphic, a graphics
card driver version (Word is tough on drivers when it
comes to graphics use) or printer/color correction.

How are you creating the PNG graphics, what type of
monitor and graphics card are you using and what are
the property settings for the graphics card in Windows?

Is it just on screen that you're having an issue or
when the graphic prints?

If you switch to another printer driver in File->Print
do you have the same result?

Do you get the same result if you use a new document
as you do with an existing one?

What are the settings in
Tools=>Options=>General=>Web Options=>Pictures?

Do the pictures change in appearance in Word & in
File=>Web Preview in Word when viewed in the browser.


=======I'm assembling user manuals from a bunch of extant "chapter" docs. These have
embedded screenshot images, many of which need to be updated. To cut down
file size I want to link the new ones to files. The current image files are
mostly PNGs with some BMPs. I've snagged some new screenshots, but the very
first PNG I linked in shows up with its contrast and brightness whacked. I
can tweak these options, but I'm having a hard time getting back to the
original on-screen settings. Whereas if I link to a GIF version of the same
image it shows up perfectly with no tweaking necessary. I would use GIfs
throughout but I will need to tweak some for size, and of course that will
make them look cruddy at any other resolution than 100%. Is there some sort
of import option for the PNGs that I am missing? All the extant ones are set
at 50% / 50% for brightness and contrast, but the new one sure didn't look
right that way.

Anyone have suggestions for me? >>
 
G

Glenn Randers-Pehrson

ArtWorker said:
I'm assembling user manuals from a bunch of extant "chapter" docs. These have
embedded screenshot images, many of which need to be updated. To cut down
file size I want to link the new ones to files. The current image files are
mostly PNGs with some BMPs. I've snagged some new screenshots, but the very
first PNG I linked in shows up with its contrast and brightness whacked. I
can tweak these options, but I'm having a hard time getting back to the
original on-screen settings. Whereas if I link to a GIF version of the same
image it shows up perfectly with no tweaking necessary. I would use GIfs
throughout but I will need to tweak some for size, and of course that will
make them look cruddy at any other resolution than 100%. Is there some sort
of import option for the PNGs that I am missing? All the extant ones are set
at 50% / 50% for brightness and contrast, but the new one sure didn't look
right that way.

Anyone have suggestions for me? >>
Click to expand...

You can try removing the gAMA chunk. The "pngcrush" commandline app will
do it:

pngcrush -rem gama -sRGB 1 -rem gama bad.png good.png

Get pngcrush (it's free) from pmg.sf.net in the DOWNLOAD area.

This is assuming your file is in the sRGB colorspace; it probably is
if the GIF looks OK with the same colors.

Glenn
 
A

ArtWorker

Bob,

Thanks for the reply. I am creating the graphics by simply doing keying
PrintScreen and then dumping the shot into a new Photoshop doc, then doing
whatever editing I need to do, and saving out the PSD as a PNG (or as a GIF,
or as a BMP). I'm using an HP 7500 monitor, and running True Color 1024 x
768. The display driver is Intel 82865G, and I see that the driver date is
4/15/2003, so that may be an issue there. I'll update the driver and see if I
get better results. Actually, now that I am poking around in the Device
Manager, I see that the PNP monitor drivers are dated 10/1/99!

Anyway, to continue answering your questions: I have trouble with the
graphics on printing them. as well. Again, saving the shots as BMPs or GIFs
gives me good results both on-screen and upon printing a hard copy.

I have not tried another printer driver, but will do so if the problem
cannot be resolved in some other way. This is less of a priority to me at the
moment.

Yes, I have the same problem with a new document. My saved PNG comes in with
the contrast and brightness whacked.

In Tools=>Options=>General=>Web Options=>Pictures, I have SCreen size 800 x
600 and PPI at 96. (I wonder if that is it? After I update the driver and
reboot, I'll try this suggestion and post results here.)

I have not tried Web Preview in Word -- I will do so and report back here.

Thanks again! Great suggestions!

Artie
 
A

ArtWorker

Glenn, I'll give this a try after I exhaust the possibilities Bib has raised.

Many thanks!

Artie
 
A

ArtWorker

Bob,

Interestingly, when I do a Web Preview, the PNG looks as I would like it to
look: brightness and contrast match the original page from which the shot was
made. Yet this is not what I see in the Document View. Vas is los? (I have
yet to reboot after getting new drivers, but will do that right now and
re-test.)

Artie
 
A

ArtWorker

Bob,

Okay, new drivers installed, rebooted -- I still have the problem. I changed
the PPi setting to 72 from 96 in Tools=>Options=>General=>Web
Options=>Pictures, but the problem remains.

I may try Glenn's suggestion, but I need to remain productive (this is a
temp gig) so I will probably just keep using BMPs linked to file.
Nevertheless, if you have any other ideas I'd like to hear them. I am
particularly interested to hear what you have to say about the Web Preview
thing.

Artie
 
A

ArtWorker

Glenn,

This will only resolve the problem on my machine alone, correct? I must also
be concerned with users on other machines.

Artie
 
A

ArtWorker

Glenn,

I note in the readme that there is concern with gamma in Photoshop 5.0,
which is indeed what I am using to get screenshots. Perhaps that is the root
of the problem, and if I used some other screen capture method (SnagIt, what
have you) I'd not have it.

Thoughts?

Artie
 
S

Suzanne S. Barnhill

FWIW, I can highly recommend SnagIt for screen captures. It obviates the
necessity of editing in a second app.
 
B

Bob Buckland ?:-\)

Hi Artie,

I noticed that you haven't mentioned the version of
Word you're using, but this article
http://support.microsoft.com/default.aspx?scid=kb;en-us;238559&FR=1
suggests that there may be an issue in how different
apps, even different versions fo the same app may react
to some of the abilities of Photoshop, but that too
seems to be dependent to some extent on the version of
Photoshop as shown on the example graphics on this
page.
http://user.fundy.net/morris/redirect.html?photoshop3.shtml
Note, that the information here also recommends using
PngCrush with Photoshop as Glenn mentioned (BTW Glenn
is the author of PngCrush (nice utility Glenn) <G>
and that may be a good solution. You're modifying
the graphic itself, not the monitor settings, so that
may be useful to you.


Trying an editor other than Photoshop (Snagit or
Irfanview for example) for the screen shots may
help, although that may not explain the printer
issue, where you could be running into an ICM
color matching profile issue so you may want to
try a different printer (you can install printer
drivers for printers you don't have to see if
that will affect the screen color matching).

To help test the paste issue.

1. Open a new document.

2. Use the PrntScrn key to get a screen capture.

3. Use Ctrl+V to paste it into Word.

4. Immediatly use Ctrl+X to cut it back out of Word

5. In Word use Edit=>Paste Special and select the PNG
format.

6. Check the color in Word, Web Preview and in Print.


=======
Bob,

Okay, new drivers installed, rebooted -- I still have the problem. I changed
the PPi setting to 72 from 96 in Tools=>Options=>General=>Web
Options=>Pictures, but the problem remains.

I may try Glenn's suggestion, but I need to remain productive (this is a
temp gig) so I will probably just keep using BMPs linked to file.
Nevertheless, if you have any other ideas I'd like to hear them. I am
particularly interested to hear what you have to say about the Web Preview
thing.

Artie >>
 
A

ArtWorker

Suzanne, I have used SnagIt before and liked it. But this is a temp gig and I
am sure my employer won't want to spend the money. (I wouldn't have gotten as
far as I have if I didn't have my own copy of Photoshop to install.) I
believe the original author of the docs I am editing used RoboHelp to grabn
screens, but it isn't on this computer and I am not terribly familiar with
it. I may need IT's help to find it on the LAN, or wherever they are hiding
it. But thanks for the suggestion.

Artie
 
A

ArtWorker

I did mention my Word version, actually, in my 3rd post -- Word 2002.

SnagIt costs money, and my employers here will be reluctant to spend it.
I've looked at IrfanView; I've just downloaded it and will give it a try. I'm
not much of a code monkey so I'd rather mess with IV than try Glenn's
pngcrush just yet.

BTW the printer issue is of less concern to me. There are only B&W printers
here anyway... I know the issue remains for printing because I can see the
difference in output on the hardcopies. Frankly I don't think it is going to
be much of an issue.

I'll try your paste method after I get done playing with IrfanView.

Thanks again!

Artie
 
G

Glenn Randers-Pehrson

ArtWorker said:
Glenn,

I note in the readme that there is concern with gamma in Photoshop 5.0,
which is indeed what I am using to get screenshots. Perhaps that is the root
of the problem, and if I used some other screen capture method (SnagIt, what
have you) I'd not have it.

Thoughts?
Click to expand...

There was a problem with PS 5.0 but the problem here is even when the
gamma value in the PNG file is correct, MSIE botches it. MSIE will exhibit
the problem when you use *any* screen capture software that writes a
gAMA chunk in its output PNG files.

Putting an sRGB chunk in the PNG instead of gAMA serves the same purpose,
because "sRGB" implies a specific gamma value (1/2.2), and MSIE fails
to botch that because it ignores the sRGB chunk and assumes gamma=1/2.2.
If that sounds stupid, it is, but MSIE does produce the correct result
because of compensating stupidities. Meanwhile, Firefox and other
browsers get it right because they recognize the sRGB chunk and handle
it correctly.

Glenn
 
G

Glenn Randers-Pehrson

ArtWorker said:
Glenn,

This will only resolve the problem on my machine alone, correct? I must also
be concerned with users on other machines.
Click to expand...

No, it should produce a correct display on all platforms. I believe even
MSIE-Mac handles the PNG sRGB chunk correctly.

Glenn
 
A

ArtWorker

Yet another good reason to use Firefox... nice little browser. I use it at
home al lthe time now. But my client uses MSIE. *sigh*
 

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