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Colour Correction


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#1 maddog

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Posted 04 June 2012 - 02:16 PM

My old CRT monitor, lost one of it's primary colours recently.  Red and blue, do not make our colourful world look good enough, without green.  So I found an old LCD monitor for sale.  It cost me little money, because it's screen was dull, and it's colours were strange, and fuzzy?  I decided to use the monitor's built-in controls, to try and improve things. :blink:  

It took only a few minutes to realize I could decrease the brightness and contrast, and then increase the saturation of each colour, until together, they produced a realistic balance.  This brought a brighter, more realistic screen to life, and with turning the sharpness up, the old LCD now looks good! :)

The visual colour correction was not small - from 50 x 3, to 76 74 70.  The trouble is, I've no guarantee, these colours are now realistically balanced together.  I've no physical colour reference - or extra monitor to compare my screen with.  So I've used only guesswork. :huh:

I wonder how many of us, are viewing the computing world, with strange and unspecified shades of colour?  Is there an easy fix?
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#2 sky

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Posted 04 June 2012 - 02:27 PM

the easiest would be borrowing a whaddayacallit? them things you plonk on the screen to calibrate the colours. i would love to have one, but since leaving my old job a decade ago, i don't have access. so nowadays my 3 screen setup shows 3 different sets of colours (AWESOME!). i use one for reference and try to match the others, but not really getting 100% match ever. the tft screens for instance can hardly get a true black - actually only the ones that cost about as much as these 3 screens cost together when all of them were new could do that.

#3 MECH

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Posted 04 June 2012 - 03:49 PM

Well apart from the calibrating tool there are some other means to calibrate your screen calibrate screen

But normally you would have to calibrate your printer as well ;)

More calibra...
Google can help sometimes... :D
Must admit I never did use it when setting up photoshop but I have a pretty lazy attitude when it comes to sound & image.
Well let's say i'm easily satisfied  :)

Cheers,

Martin


#4 maddog

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Posted 05 June 2012 - 01:45 PM

Thanks MECH - that's a useful site!  I tested the screen, and my LCD is working well.  That site is very good at checking the screens black & white qualities.  I still want to check the colour balance. :rainbow:

What's needed is a visual colour reference. One way to try this, would be to print a picture from the screen, and then compare the result, with the screen. But that would obviously rely on the printer's accuracy.  So . . . instead the reverse could be done - scan an image into the computer, and compare.  But wait, same problem - how accurate is the scanner?  Probably better than the printer? :matrix:

This might make a good topic for a computer enthusiast magazine?  An article could include a page made up of binary and tertiary colours, and a simple HTML page to copy, to display the printed colours on your screen.  I wonder if it's been done already?  I can think of only 1 possible reason why not -  what if the magazine printers colours are inaccurate !  :ranting2:

Edited by maddog, 05 June 2012 - 03:46 PM.

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#5 TvO

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Posted 06 June 2012 - 01:24 AM

This might be a useless idea, but if I recall correctly newspapers have colored dots on the edge of some pages, possibly to aid some sort of calibration method of colors lining up on the press. Perhaps you can compare the dots to the screen calibration page linked by Mech to see if your monitor gives the correct color.

Tommie.

#6 MECH

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Posted 06 June 2012 - 05:15 AM

View Postmaddog, on 05 June 2012 - 01:45 PM, said:

What's needed is a visual colour reference. One way to try this, would be to print a picture from the screen, and then compare the result, with the screen. But that would obviously rely on the printer's accuracy.  So . . . instead the reverse could be done - scan an image into the computer, and compare.  But wait, same problem - how accurate is the scanner?  Probably better than the printer? :matrix:

Comparing printed colors with screen colors is not something i would do.
A printed image is giving it's color info based on what color it reflects(or better said which colors it filters out) e.g. it is a perception of reflection.
A monitor radiates a light wave based on the mix of Red Green & Blue emitting light which is a different method. The problem with pc's is that each program has it's own interpretation of coloring. Photoshop has a calibration standard that can be used to make sure you use the same coloring method.

Then there is your own perception of color as well. If you would compare the color settings of a TV in a couple of houses you would see a lot of differences.
For me it's a matter of does it look good?; yes then leave it alone. I've had my share of trouble fixing stuff i changed because i read a topic somewhere stating i had something not the same as everyone else. If it works don't try to fix it  :D

You know those little annoyances you normally not care about untill someone points them out to you and then start becomming a big deal.. :P

Cheers,

Martin


#7 maddog

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Posted 06 June 2012 - 06:50 AM

Hi Tommie,

A responce to MECH first.  I have to agree that exact colour reproduction, isn't usually necessary.  In the USA, I could switch between the 3 major TV channels, and each had their own distinct colour tint - one was greenish yellow, one was too red!  This didn't seem to bother most viewers?  But where artists are involved, such as our Sims mod teams, colours become important. For instance, there was a recent discussion on the exact tint, of a Ferrari from 1971.  This becomes meaningless, if the artists all see the same colour differently! :think:

Tommie's idea is interesting - professional newspaper printer ink, should produce more accurate colours, than a home printer, to check against the 3 primary colours on the monitor?

In scientific terms, we have 3 specific colour frequencies, to check.  But I'm not sure these would change, and cause problems?  My guess is, after starting out with a rainbow of realistic colours, when new, it's the intensity of the 3 which changes, and changes their combined tint. :bandana1:   So how now, to check the brightness/intensity of each, without accurate scientific equipment?  It's actually quite simple, when you're properly equipped.

Combining red and blue equally on your screen, should produce an exact colour. Likewise with red and green.  If one is brighter than the other, the combined colour will look different - the tint will be wrong. :ermm:   To see what's right, we'd need to compare the screen with the correct combined colour.  ATM, I don't have those exact combined colours to check against.  So my best thought is a scanned photograph, to compare with.  If anyone knows how to photograph a GPL car, that might be good too !  :D

Edited by maddog, 06 June 2012 - 07:13 AM.

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#8 thl

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Posted 06 June 2012 - 11:56 AM

You need a spetrophotometer or a colorimeter to make a profile for your monitor - best results with expensive monitors. There's no other way to get colours right. In my company nearly every monitor has such a profile made with spectrophotometers or colorimeters, so I know what I am talking about. Furthermore you need D50 lamps in the room (that's light with 5000 Kelvin).

#9 MECH

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Posted 06 June 2012 - 12:05 PM

View Postmaddog, on 06 June 2012 - 06:50 AM, said:

Hi Tommie,

A responce to MECH first.  I have to agree that exact colour reproduction, isn't usually necessary.  In the USA, I could switch between the 3 major TV channels, and each had their own distinct colour tint - one was greenish yellow, one was too red!  This didn't seem to bother most viewers?  But where artists are involved, such as our Sims mod teams, colours become important. For instance, there was a recent discussion on the exact tint, of a Ferrari from 1971.  This becomes meaningless, if the artists all see the same colour differently! :think:
You have a strong point there and if the base is wrong then the ones using it will by default have the wrong colors.
Although the question would be how many can judge it properly when using uncalibrated monitors ;)

Cheers,

Martin


#10 MECH

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Posted 06 June 2012 - 12:16 PM

View Postthl, on 06 June 2012 - 11:56 AM, said:

Furthermore you need D50 lamps in the room (that's light with 5000 Kelvin).
Yup, in order to determine colors properly you need white light e.g. the higher temperature range in Kelvin.
Although that's not a 100% garantuee it gives accurate coloring. The light source needs to have full spectrum light as well  :)
Besides fluorescent lights degrade over years and need to be replaced at a certain clipping point.
Most of the time you would be amazed about the loss of light over the years.

Cheers,

Martin


#11 maddog

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Posted 07 June 2012 - 04:53 AM

Agreed - expert equipment would tell the story best.  The best equipment most of us have, are our eyes, and our eyes are easily to fool.  My quest is to reach towards, foolproof calibration by eye.

I've written some html pages, to display primary and secondary colours.Each page should display an exact colour.  The binary pairs, should create a specific shade from their 2 equal halves.  Now, if I had something actually printed in black and white, umm . . . in colour, to check them against, I could visually correct any monitor, to approximately where it was intended to be.  The specific secondary colours needed, must be realistically printed somewhere, for reference purposes?  Without them, we are living in a nonspecific, uncalibrated, wonderland of colour! :D
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#12 thl

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Posted 07 June 2012 - 12:20 PM

Hm ... I think it's not possible because a monitor works with RGB colours, printers with CMYK colour space.

First problem:
You will need a very good printer, a so-called proofing system working according to some standard (in Europe we have ISO 12647, in Germany PSO) to get colours right. Such a printer is very expensive (but there are online printing services who can do that for you - but you need CMYK-colours with a special colour profile!). A desktop printer is inappropriate for such a job.

Second problem:
RGB and CMYK are two very different systems:
RGB (monitor) = additive color, mixing of light
CMYK (printing) = subtractive colours, light is removed from various part of the visible spectrum to create colours
And: RGB colour spaces are much bigger than CMYK colour spaces, many RGB colours can't be printed, especially very saturated colours such as RGB green! Here's a good link where this effect is demonstrated:

http://en.wikipedia...._comparison.png

So printing and comparing is not a good idea, especially printing and comparing RGB colours.

#13 maddog

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Posted 08 June 2012 - 04:12 AM

My eyes tell me that comparing a luminous screen, to a printed colour is not going to be the preferred method.  Can I borrow one of those fully calibrated screens thl?  Meanwhile, a scanned image, which can be compared with the ink it's copied from, seems the best practical 'home' method I can think of.  The scanner would have to be accurate though, with no tint! (5000K ?)  A head and shoulders portrait of a person, perhaps?  Skin tones and some bright clothing should make them easier to compare. :cool:

Before anyone panics, I would like to think the monitors we use, create realistic colours when new?   Mine was manufactured in 08.2007  Seems to me,it's colour reproduction has changed with age, which is why it was sold to me. :ermm:

I wonder thl, if the equipment you mention, has been used to test ordinary TFT, and LCD, monitors, new and used?  I'd be interested to know how accurate, or how inaccurate ours generally are, at reproducing colours properly.  :think:
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#14 thl

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Posted 09 June 2012 - 04:00 AM

I don't think you can borrow fully calibrated screens somewhere.
There are some "cheaper" hardware calibration tools available (cost upwards of 175 dollars), have a look here:
http://www.drycreekp...ation_tools.htm
(Tool A is well-known)

Scanning method: depends on how good your scanner is. Especially brown, grey and other dark colours can become nearly black on low-end scanners.

At work (printing company) we have a colour management system. That's great! You can scan a photo, it looks exactly the same on the monitor and then you can print it on a special printer, and again it looks the same. But that's only possible because every device has its own profile, we had to create (that means a lot of work): Scanner, monitor and printer. But I think less than 1 percent of people have heard of colour management in their life. Most people don't care about that.

And no need to panic;-) Most monitors are good. And yes, colour reproduction changes slightly with age, that's normal.
There are many graphic updates for GPL I have installed and they are all looking good. So I think nobody in the developer team has a big problem;-)

Which equipment is used to test monitors - well I don't know, I'm not a monitor tester.

But another consideration:
I think maybe 99 percent of people having GPL have a "normal" monitor without correct calibration and profiles.
And GPL itself does not use any profile, as far as I know.
So I think it is not absolutely essential for graphic teams to have 100 percent correct monitors, because nearly nobody out there has such a system and GPL itself doesn't use colour profiles. Maybe it's better to have a typical monitor with typical settings.

From my experience there are some main differences between calibrated/with profile and non calibrated.
Color-consistent systems have less brightness, less contrast and less saturation. Differences in colours (hue) should be rather rare - most monitors are quite ok in dealing with colours - but colour temperature in default monitor settings is often quite high, it's maybe a bit blueish with default settings.
So most "normal" monitors are too bright, have too much contrast und too much saturation. This is because photos will look better on them and that's why people buy them. Nobody wants to have greyish and dark colours. This is economic law of supply and demand and monitor manufacturers are adapting to the needs of people.

At home I have a quite common monitor (TFT display) from S.....G, settings are default, in my company I have an expensive monitor, calibrated and with profile. I made a screenshot of the current Spa67 project, and watching it on these two different monitors visual impression is slightly different.
I tried to simulate the difference in photoshop (it's about visual impression, and it can differ from monitor to monitor, but I think it's the typical deviation). (picture attached)

The eye quickly got used to a colour set, so the overall impression will be very similar after a few minutes I think.

For people working on graphics a good approach can be to search for high quality photos - very suitable are high quality digital photos - without any colour casts and bring colours on a one-to-one basis to gpl. In photoshop, for instance, you can measure colours and copy them into a texture by using a layer with blending mode "color". If you don't have photoshop you can judge "by eye".

All in all, colour correction is a very interesting topic, but it can be complicated as well;-)

Thomas L.

#15 maddog

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Posted 09 June 2012 - 02:52 PM

It's good to get some information, from someone with a real insight into this matter.  Many thanks Thomas! :)

So, from this discussion it seems likely, our monitors colour reproduction will become less reliable with age.  Comparing a photograph to it's scanned image, might help to identify a problem.  But checking an old monitor against a new one, might do the same job better.  And for those who want to spend money, there are tools which can remove the word, 'might'. :2c:
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#16 thl

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Posted 11 June 2012 - 12:43 PM

It has been a pleasure for me to talk about this interesting things.
I think you're an expert now.  :thumbup: