Zone system, brightness values of different parts of RAW image

[peanutLion]

Is anyone taking photos using the zone system? I need your help to tweek exposure in Affinity Photo.

 

My question is this: is it possible to see the luminance brightness value of any part of a RAW image in the Affinity Photo develop persona (or any other persona) by putting the mouse pointer over that part of the image?

 

I don't care about the individual colour brightness values of R, G and B. I want to know the luminance brightness value of a pixel.

 

The RAW processing software that came with my camera allows me to do this but that app just keeps crashing all the time!

 

Here's what I want to do in real life:

 

i) Take a RAW picture of a scene that contains a grey card 

 

ii)  Open the RAW image in Affinity Photo's develop persona (or maybe another persona)

 

iii) Run my mouse pointer over the grey card in the image and move the exposure slider in the persona until the corresponding luminance brightness value of the pixel under the mouse pointer falls on zone 5.

 

To be able to do iii) above I need to be able to see the luminance brightness values of any part of the RAW image as I run my mouse pointer over it. I want to be able to put my mouse pointer over the grey card in the image and look at the corresponding brightness value. The luminance brightness value for any pixel goes from 0 to 255.

 

So let's say that my camera gives a pixel a luminance brightness value of 135 if that pixel is in a part of the scene that really is on zone 5 (like a grey card would be if I got my camera aperture/exposure time correct). Then let's say I've actually taken a picture and overexposed it (maybe to do the ETTR thing) so that the brightness value of any pixel of the grey card is actually, let's say, 150. To correct the exposure in a persona of Affinity Photo, I would really like to simply put the mouse pointer over the grey card in the RAW image and move the exposure slider down until the luminance brightness value is 135.

 

Is this possible in Affinity Photo?

 

The photo shows the histogram of a scene containing a grey card placed on zone 5 (actually the grey card is the small bump in the middle of the picture). The histogram comes from my camera maker's Raw processing app. Although the photo doesn't show the brightness value of the peak of the middle bump, it's actually 135.

 

Any help would be much appreciated.

zone5bump.tiff

[Pedro Soares]

Hi peanutLion, Welcome to the Forum :)

 

I also use the Zone System. I even created a Gradient Style where I can pick and compare the value of the zones I want to measure (you can create the gradient by hand or using the Posterise Adjustment). My idea is to create a repeatable workflow in Affinity Photo. Until know I never used AP to do what you want to achieve since I use Capture One Pro for my RAW images.

 

Nevertheless when I want to measure the Lightness of a given colour, I use the Info Panel. I just add a new Sampler, set it to Lab Colour Mode and place it over the colour I want to measure. Then I can correct it accordingly. Not sure if this could help you but most of the times it works for me.

 

Cheers,

Pedro

[rmar]

I use the NIK plugins to do this. They work in Affinity. They're free so I haven't played much with Affinity's tools. That's all I can add.

 

Is this similar to what you are trying to do? https://www.youtube.com/watch?v=ESamxjp-b18

[peanutLion]

Many thanks, Pedro.

 

I learned something when you mentioned the info panel – I didn't know that existed!

 

Many thanks, rmar, too.

 

The video was interesting and I now know that I will have to try Nik plug-ins.

 

:) 

[rmar]

Here's another fun way to use NIK (replace references to photoshop with Affinity Photo)

You can use NIK to do some really easy fixes to a color image. You don't have to use it for B&W exclusively.

More experienced AP users might not need this but it works great for me.

 

https://blogarithms.com/2013/02/06/sfxpro-for-color/

http://www.northlight-images.co.uk/using-silver-efex-pro-for-colour-prints/

[Pedro Soares]

You're welcome peanutLion, I'm glad I could help.

 

I forgot to mention that I also use Nik Plugins (a lot) and as rmar said, they are an excellent option for your needs. I specially like and use Silver Efex Pro 2 for many of my black and white work. Check below the Histogram and you'll find the Zone System. You can choose the zone you want and then correct your image with U-Points to place a specific area of the image inside that zone.

 

Cheers,

Pedro

[peanutLion]

I can’t wait to get my hands on the Nik plugins mentioned here as they seem very interesting. I particularly like the way one zone can be converted to another.

 

In the mean time, I’ve just discovered a difference between Affinity Photo and my camera’s RAW conversion app (Nikon Capture NX-D): the histogram is different for the same RAW image. This may be useful to know if you have been editing RAW images in Capture NX-D but are now switching to Afinity Photo.

 

The RAW image in the preview screen of Affinity Photo is not really represented by the histogram. The preview screen actually shows a RAW image that must be screen-gamma corrected, in my opinion, so that you can see it properly on your computer screen.

 

However, the histogram of the RAW image in Affinity Photo is not gamma-corrected (but it is in Capture NX-D!). And sampling a part of the RAW image in Affinity Photo with a sampler from the info panel gives you L values (from the HSL colour model) that correspond to the histogram (which actually means they are lower than you might expect).

 

Once you convert the Affinity Photo RAW image to, let’s say, a TIFF, and then load the TIFF into Affinity Photo, any L value in the TIFF is now greater than the L value for the same part of the RAW image (because creating a TIFF includes correction for computer-screen gamma, and that process shifts the histogram to the right).

 

So this is going to be my workflow for ensuring that a RAW image’s exposure is correct in Affinity Photo (before converting it to a TIFF or JPEG or something):

 

1) Open the RAW image and correct the white balance, contrast and other stuff.

 

2) Let’s say the image has a grey card in it. Call up an info panel and sample the grey card using the HSL colour model.

 

3) Move the exposure slider until the L value of the sampled point is 18% (assuming I want my grey card on zone 5 and assuming I have made sure my camera’s histogram showed no clipping). Btw, I think there will be a bit of to-ing and fro-ing between 1) and 3).

 

I have determined that a RAW image pixel will be correctly on zone 5 when its L value is 18%. I determined this by loading into Affinity Photo a RAW image that contained a correctly camera-exposed zone 5 area and then sampling pixels in that area of the image.

 

The same can be done for all the other zones. I have determined that a zone 6, for example, gives an L value of 42% (although that figure may be a little off the real value because my experiments were not quite as accurate as they could have been!).

 

If anyone thinks there is anything wrong with my logic I would be very happy to be corrected. :)