Art reproduction - how to even out brightness and color in a picture based on another (blank( reference picture

[sonosandro]

Hi all, first post here! Thank you all already for the help received even by just scrolling the forums in the past.

 

SHORT: During art reproduction, how can I make sure that the brightness is even throughout the whole picture, and that the lighting used is not affecting colours too much?

LONG: I need to photograph some paintings (about half meter in size, in average) and also some small-ish craft objects, some of them reflective, and I would like to minimize the error from uneven light distribution, and possibly to use a color chart to try to get the colors as right as possible.

Scanning, which would be the obvious solution, is often not an option.

Some paintings cannot be taken out of the glass=reflection (some of the owners do not want to) and some objects are shiny. I looked online and the solution to reflections would be to use two polarizers, one at the light source (speedlight or video light) and the other at the camera. This will remove reflections, but for this to work I cannot have any stray or ambient light, therefore I have to create a lightbox, or kill ambient light in camera. Which means that the only light source will be my artificial light, and probably it won't be evenly distributed as sunlight would be. Light will come from both sides, diagonal. I can feather the lights and play around, but still I believe that the illumination won't be even throughout.

The imperfections coming from the lens are taken care of by the in-camera corrections. (I will be using a Lumix S1 with the 24-105 f/4, possibly with HighRes mode if I can get hold of video lights strong enough, since the HighRes mode does not support flash)

I am worried about the errors that I introduce with:

1-uneven light distribution

2-colour fidelity not adequate

Regarding point 1, I looked online and all i could find is Lens Cast Correction LCC for CaptureOne (which I don't have..). But that seems to correct the lens, and not the scene. I was thinking of shooting before each painting a piece of white material (or grey or whatever is best)in the same position where the painting will then be placed, to "map" the light distribution under the same setting at which I would be shooting the artwork, to create sort of a "correction layer"to correct locally the brightness of the final image.

And also to shoot a colour chart (again with the same setting) to have some sort of reference for colours.

Any idea how to implement point 1 or 2 or both?

Also, any other advice, or a different approach to the problem?

I have Affinity Photo 2, I am not a pro user, but if somebody would at least point me in the right direction...)

Is this problem solvable in Affinity Photo, or in which direction should I search?

Sorry for the long question, but it is quite a new area for me.

Thank you all in advance for the replies!

 

[user_0815]

This sounds like an interesting project. 
 

1. the uneven light can be managed by light modifiers and/or light sources. Depending on the location, you could consider large diffusers between the object and the light sources. This will even out the light and also help with reflections. Larger is better in this case. If possible, I would bring my own light sources and avoid all other lights. This would help for best possible and even lighting and avoid nasty colour cast due to different light sources. 
 

2. use a colour checker or at least a grey card. With a colour checker you can reproduce colours accurately. Afaik DXO photolab supports using a colour checker. Idk about others. 
otherwise, if you have references regarding the colours like rgb or Pantone values, you can dial them in with HSL in affinity in post. 

[sonosandro]

@user_0815 Thank for the reply. After the holidays I will try to do some tests and see how much of a problem the light fall off actually is. Since the whole setup would have to be minimal for traveling, I was hoping to avoid large equipment, but in the end I believe it is better to get it right in camera. I also have to test if I will use flash (no HighRes mode available, simple setup) or video lights (big and expensive but I can use HighRes) and balance pros and cons. I'll post back if I have some interesting results.

Thanks so far!

[qwz]

If possible, take a shot of your light setup with a complete blank white/grey background. So, you can later substract this picture from resulting ones i.e. light uneveness, color cast (including lens color cast), sensor dust etc. Better also to have such picture with (slightly) defocused lens.

Capture One Pro has such function called LCC, but it can be replicated in Affinity Photo via layers 

[thomaso]

On 8/18/2024 at 4:55 PM, sonosandro said:

solution to reflections would be to use two polarizers, one at the light source (speedlight or video light) and the other at the camera.

For the camera you should get a circular filter, it is more efficient than a linear version. Depending on the lighting conditions, this may be sufficient and may not necessarily require additional filters for the two light sources (-> larger filter size + price). Also the quality of filters can vary considerably in terms of efficiency, homogeneity and price. This article may be interesting: 

https://www.lenstip.com/115.1-article-Polarizing_filters_test_Introduction.html

On 8/18/2024 at 4:55 PM, sonosandro said:

shooting before each painting a piece of white material (or grey or whatever is best)in the same position where the painting will then be placed, to "map" the light distribution under the same setting at which I would be shooting the artwork, to create sort of a "correction layer"

Assuming the light position and intensity does not change for different object sizes during a session, you may not need this white control image ("correction plane") for each individual object but only one for a certain camera position.

When changing the camera position (distance, height), you also need to adjust the angle each time to ensure parallelism between the sensor and the paintings and to take into account changing reflections. Therefore, it may be more convenient (and faster) to start with the largest painting for the maximum distance and possibly use the zoom for smaller objects, possibly with the appropriate cropping of the "correction layer" image. (Of course, 3D objects require different settings than flat paintings/drawings)

[Greg E]

When shooting items under glass, I always shoot at a slight angle, to keep reflections out of the image (even if your lights are well placed, you may see a reflection of the camera). Then, apply a perspective correction before cropping. Don't crop too tightly in the camera--even if you are reproducing the artwork without the frame, the frame or matte are very useful for judging the perspective correction.

[NotMyFault]

In many cases  apps like PhotoScan (from Google) do the best job to remove reflections from images.

It (helps you to) takes multiple shots (4, from each corner) and removes spot reflections computationally. It does not help if you have a global/diffuse reflection which reduces contrast globally.

pro:

• works with phone only, no tripod or other equipment required
• fast and good results in general, for spot reflections

cons

• quality limited to your phone camera
• handheld may introduce motion blurriness 
• you need to accept google T&C

 

[firstdefence]

On 8/18/2024 at 3:55 PM, sonosandro said:

SHORT: During art reproduction, how can I make sure that the brightness is even throughout the whole picture, and that the lighting used is not affecting colours too much?

Use diffused light so that shadows aren't cast, this can be done fairly cheaply using bed sheets or buying some translucent fabric.

On 8/18/2024 at 3:55 PM, sonosandro said:

LONG: I need to photograph some paintings (about half meter in size, in average) and also some small-ish craft objects, some of them reflective, and I would like to minimize the error from uneven light distribution, and possibly to use a color chart to try to get the colors as right as possible.

Take the photograph through a hole in black card that is parallel to the artwork and obviously do not use flash.