Pictures of a dark violet flower appear light blue. Is this a lens or a technique problem?

Question

I just got this Tamron AF 70-300mm 4-5,6 Di LD Macro 1:2 for my Canon 500D.

I tested it yesterday and it works fine. Only one problem: I took pictures of a flower which is dark violet. But when I look at the pictures on screen, the color is kind of light blue, which is a big difference. I use a UV filter and the sun block hood, and there was no sun light at that moment. I changed to my Canon 55-250mm, and it didn't have the same problem.

I don't know if this is a technique problem, or an issue with this lens. Does anyone have the same experience?

This is the one I took with Tamron, I resized it:

And this one I took with my Galaxy S7:

Answer 1

The flower is supposed to be dark violet, but it's come out light blue.

That indicates the image is overexposed. If the flower is dark, the image of the flower should be a similar tone. So for a start you need to lower the exposure and darken the flower.

The reason for the color change from violet to blue is that the reds in the image are blown (or clipped) (see also Why are red objects coming out unnaturally in my photos?) It is common in photographing red objects that they come out pink or even orange. When you have a purple object, overexpose somewhat and blow out the red channel, but not the blue channel, then you may end up with a light violet or blue.

Look for the reds being at the extreme right of the histogram like this:

and lower the exposure, or use exposure bracketing, until they are not blown.

Edit: now that you've posted examples, it looks like it may simply be the BLUE channel blown a bit.

Again, just try lowering the exposure a bit.

Answer 2

Despite you saying that this does not happen with 55-250mm objective I claim that this is the problem with camera settings. If you finally upload the photograph made with 500D and 55-250mm I may update the answer.

Cameras do not generally make neutral images because it is impossible to clip while selling cameras which do not produce the image which make your friends astonished. Cameras do bump chromatic saturation and they do bump contrast. It seems that you have set the contrast and saturation too high and this is obvious because of harsh transitions between different colours:

I have taken your sample image and made it even worse using the algorythms which cameras are broadly using.

Here is a saturation bump:

Here is a contrast increase:

You may see that flowers became even more blue than they already were.

Also, here is an illustration of exposure not being the cause of bluish tint:

I have further increased exposure and it only made flower look more violet.

Your solution is to:

1. drive contrast and saturation back
2. decrease the exposure because the blue channel seems to be clipped
3. if that is not enough try altering the white balance because it seems to be off compared to photo from smartphone (too "cold" what worsens the bluish tint cause by saturation and contrast bump).

Here is the blue (not red) channel of your image which does not contain details of flowers:

Interesting thing is that this clipping well may be caused by the bump of contrast and saturation because of how limited sRGB is: a ProPhoto triplet (50,10,200) does not have an sRGB equivalent and will be something like (20,0,255) after absolute colorimetric conversion, and increasing saturation and contrast makes it only worse.

Answer 3

1. This is not a problem with the lens
2. There are several possible reasons why this can happen, some trickier than others. But most likely problem is the color balance. You probably used automatic color balance settings on your camera and since there are only limited colors in the picture, the scene was not evaluated correctly. You should be able to fix that in a photo editor.

Answer 4

It is neither a lens nor a technique problem.

There are instances where trying to capture true renditions of naturally occurring hues is not possible. The morning glory bloom is one specific example.

Violet is one hue with wavelengths that cannot be artificially reproduced at the present. Your subject pictured above appears to be in that category. The closest we can come with pigments and/or other colourants is purple (a mix of red and blue). As soon as you compare a reproduction with the original, the difference is evident.

The difficulty is the hue is not within the spectral sensitivity of the sensor. It out of the sensor's "gamut," if you will. This also happens with light-sensitive film emulsions or any system which only approximate human vision.

Answer 5

This happens with film also. Violet can be approximated with blue and red mixed up, but in reality, violet can be a single wavelength. The camera's sensor (or three colour film emulsion) measures the quantity of light energy in three bins, the blue 'bin' (475nm) being the one for the shortest wavelengths, and so violet (400 mm - a shorter wavelength than blue which is at 475 mm) is in that same blue bin. The other 'bins' are green (500 nm) and red (650 nm). The red sensor (a longer wavelength at about 650 mm) does not pick up any of the violet, so you get blue (475) where violet (400) used to be. To accommodate this, a fourth sensor could be used to grab the violet at the expense of resolution, but I think in film the extra layer would be an issue in terms of a complementary dye coupler. Adding an additional sensitizing dye to the red layer on film is probably not possible because the red layer is underneath the yellow filter layer. If colour reproduction of violet was important, one green cell in the mask pattern of a digital sensor could possibly be swapped out for violet, in theory.