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Why does purple show up as blue in the photo?

JO ROSE , Nov 17, 2010; 02:04 a.m.

Hi,
just found this forum whilst googling, am hoping it will become a bit of a companion for me whilst I pursue my hobby as I will be hungry for advice!
I am using an Olympus e-420 and taking some photos I've noticed that if often portrays purple as blue.
Can anyone tell me why this is and how I can correct it?
Yesterday I photographed a multicoloured dress next to a purple Chevy. The purple in the dress was the same as the Chev yet it looked blue in the dress while the car still looked purple.
I've had this happen in my handheld digital camera in the past too.
I'm hoping it's an easy fix,

thanks for your help,
cheers,
Jo

Large photo attachment:
(purple_blue -- 853 x 640 photo)

Responses


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Joe C , Nov 17, 2010; 03:18 a.m.

The cause may have to do with the fact that your eyes can see the difference between blue and violet light, but many cameras cannot. Similarly the camera may be able to see the difference between violet and magenta in cases where your eyes cannot.

The car may have been magenta instead of violet, meaning that it reflected red light too, so that the camera may have captured both blue and red. If the dress was violet, then the camera may have captured only blue.

Fixing this would be more difficult, and would probably require making a selection or mask to avoid changing the car and then adjusting the hue of blue in the dress. Here is a quick and dirty version in about a minute, but doing it carefully should not take that much longer.

Large photo attachment:
(Edited -- 853 x 640 photo)

Andrew Gilchrist , Nov 17, 2010; 03:30 a.m.

Let me guess, you shot this with flash. I have had similar problems, photographing a sort of irridescent purple handbag that came out looking not purple at all, but blue. Solution was to fix in post--white balance wouldn't fix it--I had to adjust the hue of the blues away from green, towards purple. Changes like these made during RAW processing have no negative effects on quality, this change was easy in Adobe Lightroom, a single slider. Since your scene is a little more complex, you'd probably want to localize the change to include just the dress.

JO ROSE , Nov 17, 2010; 04:05 a.m.

Andrew - I shot the dress about a hundred times over the course of the afternoon with and without flash and with varying degrees of flash. Different lenses too. No success in any of them.
Actually in the photo I submitted here the purple looks the best out of all the pictures I took.
I should start taking photos in RAW, Ive been taking the scardycat option and just doing JPG. I fiddled a bit with colour just using Irfanview as it's just a simple program I've become comfortable with. I do have photoshop but havent put in the time to learn it well. I fiddled with the blue and red without success but I didnt think about fiddling with the green slider. Might be a bugger that most of the shots are in luscious green gardens lol
I'll have a peek at Adobe Lightroom, thanks heaps.
Joe - thankyou for shedding the light on why it happens. I had googled a few days before taking the pictures (as soon as I heard there was purple in the dress) but I couldnt find much to help me.

This lovely girl was the date of my friend's son at their prom and I felt bad I couldnt capture her dress well as it was really vibrant

Jo

JO ROSE , Nov 17, 2010; 04:22 a.m.

hehe, Joe I didnt realise you had posted the photo of the fixup - it looks good. The funny thing is I was looking at it just thinking it was mine repeated and thinking , 'actually it's not as bad as I thought it was'.

And wondering why your last sentence ended how it did with no 'fix instructions' for me to follow.

Oh dear....

I'm actually not a dopey person believe it or not lol

Joe C , Nov 17, 2010; 04:33 a.m.

Sorry, to me that was the instructions, and I used GIMP, but the gist ought to apply to any software. In more detail:

  1. I used the lasso tool to draw a selection inside the car but well outside the dress except at the sill where I drew slightly inside the dress.
  2. With the dress selected I opened the Hue/Saturation control panel.
  3. I clicked on “B” for blue.
  4. I moved the Hue slider from 0 to around 32.
  5. I clicked OK.

JO ROSE , Nov 17, 2010; 05:20 a.m.

Thanks so much Joe.

I downloaded GIMP just a couple of weeks ago so I'll head into it tonight and fix the colours.

What a great result from the post, can see I'll be heading back here again :)

Alan Marcus , Nov 17, 2010; 10:35 a.m.

Human color vision is a blend; our eyes and our brain assemble what we see. This is another way of saying we see what we want to see. Actually the exact colors we think we see change minute by minute as the color of the light changes or when we move to a place, where the illumination is different. You can demonstrate this for yourself. Look through a strongly colored filter (gift-wrap cellophane will do). Place this filter to cover only one eye. Peer through this filter for a few minutes and then glance about covering one eye with your hand and then quickly switch eyes always keeping one covered. You will discover that the colors seen by the left eye are now quite different then the right eye. What has happened is the filtered eye attempts to return to normal (the unfiltered condition). Do not worry, in a few minutes your color vision will return to normal. This demonstrates natures method we call white balance in the digital world. Normally you are unaware of color vision changes because both eyes change together and you can only gauge this happening is one eye changes independently.

That being said, photo engineers have been trying to reproduce color images with fidelity since the very first color picture was demonstrated by J. Clerk Maxwell in 1861. Color pictures are separations. Three pictures are simultaneously taken. The three images represent the red, green, and blue of the vista. Color film is a sandwich of thee films and the digital chip is an array of red, green, and blue light sensors. The problem is, we have never made a film or a chip that can perform exactly like the human eye. Because this is true, photo engineers concentrate on getting certain colors right at the sacrifice of others. Generally, the maximum effort is on so-called memory colors. These are flesh tones and shades of gray and a few other very familiar colors.

Now the problem is compounded by the fact that after the picture is taken it must be displayed on a computer or TV screen or printed on paper using dye or ink. In every case the colors we are forced use, I am taking about the dyes and the pigments, all miss the mark. The best we can do is approximate what the human eye brain combination sees.

Now the purple of the car and the purple of the dress appear different when photographed because one is glossy, one is a matte, both are purple but both reflect slightly different frequencies of light. The camera's response being different than the human response magnifies the differences.

If you want more, check out Kodak's book Color AS SEEN AND PHOTOGRAPHED by Ralph M. Evens.

David Haas , Nov 17, 2010; 12:26 p.m.

Purples are one of the trickiest colors for camera sensors to get "right" for all the reasons listed above.

Sensors have gotten better - the newest ones get them close the majority of the time - especially if shot in RAW as opposed to JPEG.

My favorite story about this issue was a local hockey league that uses Blue as a primary uniform color - Team and Individual photos came back and parents started complaining - since their "Blue" was "Purple". Turns out the photographer (Not ME) used older camera's and shot in JPEG not RAW. They had no chance at all.

Dave

Dan M , Nov 17, 2010; 12:44 p.m.

Jo,

Don't be scared of shooting RAW. It adds a few quick steps, but in return, it gives you vastly more control. I did what you did, for a year. I wish I had started with RAW earlier.

One of the worst things about shooting JPG is exactly the problem you encountered: color balance. When you shoot JPGs, you are telling the camera to use a pre-set menu to develop the image, including contrast, saturation, color balance, etc. It may look great, or it may look awful. If you shoot raw, you decide those things yourself, and you can play around as long as you want without making any permanent, 'destructive' edits.

Dan


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