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Author Topic: Prints too dark but monitor calibrated  (Read 1345 times)

BobShaw

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Re: Prints too dark but monitor calibrated
« Reply #20 on: September 07, 2017, 09:10:28 PM »

If you had to choose between 55mm or 120mm macro on the 635z which would you choose for art reproduction? I know, I know... you wouldn't, you would use a hasselblad... but if you had to?
Mate, you probably need to say if the art is the size of an A4 piece of paper or 2metres square and if your room is 3m square or 10 metres square.
I doubt that it matters much as the art is only 2 dimensional. I use a 50-110 zoom most of the time because the camera is on a stand and I just fill the frame. What else are you going to do with the lens is probably more important and for most still things I use a 120mm macro in the studio. So I would say that.
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #21 on: September 08, 2017, 08:55:59 PM »

Painting is 12inx12in, room is about 17ft square

I took some more shots without using the gray card. I spot metered off several locations in the painting (the sky, the grass, the road,etc). Obviously, I got some very different readings at each location. I have aperature set at f/8, 100 ISO and I averaged the metering to where the brighter sky read 1/3 stop over exposed and the darker grass and road was 1/3 to 2/3 underexposed. I think the shot has much better exposure.

But, I have a question still about gray card use. It would seem that the gray card I was using has a higher reflectivity than the painting and therefore the exposure for the gray card was underexposed for the painting. So, since very few images have 18% reflectivity, what does a gray card actually do for you?

And another question about using the colorchecker. I created a colorchecker profile in the exact light I was shooting the painting in. If I shoot another painting of the same size such that I don't have to move camera or lights, can I use the same profile? Is there any reason to shoot the colorchecker in front of each painting I shoot? Those of you that use a colorchecker or similar what exactly is the workflow procedure and what does it do for you? I can definitely tell a difference between Adobe Standard and the custom profile (the custom profile seems to match the painting better).
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BradSmith

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Re: Prints too dark but monitor calibrated
« Reply #22 on: September 08, 2017, 09:59:52 PM »


But, I have a question still about gray card use. It would seem that the gray card I was using has a higher reflectivity than the painting and therefore the exposure for the gray card was underexposed for the painting. So, since very few images have 18% reflectivity, what does a gray card actually do for you?

And another question about using the colorchecker. I created a colorchecker profile in the exact light I was shooting the painting in. If I shoot another painting of the same size such that I don't have to move camera or lights, can I use the same profile? Is there any reason to shoot the colorchecker in front of each painting I shoot? Those of you that use a colorchecker or similar what exactly is the workflow procedure and what does it do for you? I can definitely tell a difference between Adobe Standard and the custom profile (the custom profile seems to match the painting better).

Gray Card Proper Use - place a photographic gray card in the same light as your subject (painting).  Move in real close to the card so it fills your viewfinder, but be careful you or your camera aren't shading it.  Also be sure that you aren't getting bright, specular type light reflecting from it straight at your camera. (This may have been your problem with your use of the gray card)  Meter it.  That exposure should be very close to the "correct" exposure for the painting.  It would also be very close to a meter reading from an incident light meter placed at the painting and pointing back at your camera position. 

Color checker - The 2 most common uses for the color checker are: 1.  for developing a specific camera/light color profile.  You load this into your program (Lightroom) and then apply it to each image you import with this general lighting characteristic.  What it does is slightly tweak the color output for the colors from your camera sensor to try to bring them to a "standard".  In simple terms, it slightly changes some hue/saturation output in some colors.  In my experience, no brightness or exposure changes.   For my own use, I have prepared 3 Colorchecker profiles....sunlight, shade and tungsten lighting.   2. For setting white balance.  I fold the color checker open so the large, neutral light gray panel is seen.  Again, place it into your scene with your subject lighting and take a shot. Then remove it and take your final image as normal.  Back in lightroom, import both images, applying your color checker profile, then use the white balance tool in Develop Module on the gray panel.  This sets the white balance of the panel to what it should be, neutral R=G=B.  And this new white balance should then be applied to your final image.  The colors should now be very close to "real".

Hope this helps with your understanding of what this tool does.  Lots of good YouTube tutorials on it.
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BobShaw

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Re: Prints too dark but monitor calibrated
« Reply #23 on: September 08, 2017, 10:01:06 PM »

Painting is 12inx12in, room is about 17ft square
Small painting, big room. Why 55mm? 120 would be fine and being macro gives you much better manual focus control

I took some more shots without using the gray card. I spot metered off several locations in the painting (the sky, the grass, the road,etc). Obviously, I got some very different readings at each location.
Exactly. This is why a camera meter is useless without a reference such as a grey card. Either that or you use an incident meter which measures the light arriving at the subject, not reflected off it.
I have aperature set at f/8, 100 ISO and I averaged the metering to where the brighter sky read 1/3 stop over exposed and the darker grass and road was 1/3 to 2/3 underexposed. I think the shot has much better exposure.
You are all over the shop. There is no place for "average"

But, I have a question still about gray card use. It would seem that the gray card I was using has a higher reflectivity than the painting and therefore the exposure for the gray card was underexposed for the painting. So, since very few images have 18% reflectivity, what does a gray card actually do for you?
No, it was correctly exposing the painting. If the artist wanted the painting bright then they would have used bright colours. The job in art reproduction is to reproduce, not improve. You don't change a Rembrandt into a Monet.

And another question about using the colorchecker. I created a colorchecker profile in the exact light I was shooting the painting in. If I shoot another painting of the same size such that I don't have to move camera or lights, can I use the same profile? Is there any reason to shoot the colorchecker in front of each painting I shoot? Those of you that use a colorchecker or similar what exactly is the workflow procedure and what does it do for you? I can definitely tell a difference between Adobe Standard and the custom profile (the custom profile seems to match the painting better).
No, if everything is exactly the same light and camera then once should be fine. Note that the colourcheckr can do the same as the grey card. You can set the exposure with the white. The colorcheckr is for colour accuracy. You need to fix the exposure in post anyway as the camera response is not the same as the eye. i.e., you need to make the whites white.
« Last Edit: September 08, 2017, 10:50:13 PM by BobShaw »
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #24 on: September 08, 2017, 10:58:23 PM »

Thanks BobShaw

I hear what you are saying about not trying to improve and only reproduce. The trouble is, the print is darker than the painting if I don't increase my exposure. Here is a pic of another painting (metered off gray card) and the print. I already have +20 brightness in Lightroom print module selected. Would you say it looks underexposed?

The histogram is way shifted left but obviously there are a lot of dark values in this painting so I assume this is as it should be.
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #25 on: September 08, 2017, 11:17:28 PM »

@bradsmith - thanks for your reply. I was using the spot meter on the camera and shooting the large gray card  in same light to get exposure settings  but did not zoom in to fill the frame as I am not using a zoom lens. Could this be throwing it off? I thought this was the point of a spot meter (so u didn't have to fill the frame) but maybe not.

Here is a shot of a different painting I did with metering off the painting itself. I'm actually like very much how well it matches to my eye (pic below- still slightly underexposed but much closer) but I also want to take the time to learn how to do it the "correct" way so that bugging me.
« Last Edit: September 08, 2017, 11:54:45 PM by Thenolands »
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BobShaw

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Re: Prints too dark but monitor calibrated
« Reply #26 on: September 09, 2017, 12:12:33 AM »

The trouble is, the print is darker than the painting if I don't increase my exposure. .... Would you say it looks underexposed?
It is way underexposed. That is why you should ignore the camera meter and start working with standard things. If you are not prepared to meter it properly then you need to just keep increasing the exposure until you get it right. See this image. The white needs to be white either by increasing the light or moving the exposure slide and noting the value.
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #27 on: September 09, 2017, 12:28:40 AM »

Ignore camera meter or meter properly? You mean the camera meter is no good and I should be using incident meter instead? I feel like metering off a gray card with camera meter should not be this hard. Literally all I am doing is setting at f8, 100 ISO, and changing shutter speed until the spot meter in camera is directly in the middle, keep those settings, focus, take shot of painting. How is that wrong? 

I thought that increasing exposure in post created noise, no? The artist wants the ability to print these large so I prefer not to increase noise.
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BobShaw

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Re: Prints too dark but monitor calibrated
« Reply #28 on: September 09, 2017, 01:31:06 AM »

Sorry, but myself and others don't mind investing a bit a time to help beginners. However, let's recap.

You have a camera that costs the price of a small car.
You are not sure how to get the exposure right by any method.
You want to do art reproduction.

I suggest that you re-read the information in the last two pages.
If that doesn't clarify then I suggest that you do a basic photography course covering manual exposure and metering.
Then practise on a still life object like a fruit bowl.
You should advise the artist to get another photographer who specialises in art reproduction.
Good luck
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #29 on: September 09, 2017, 02:07:24 AM »

I do appreciate your comments thus far but perhaps you could keep it on topic. I have a family member who is an artist who would like to be able to have some prints made - I am not some poser setting up an art repro shop ripping people off and giving you professionals a bad name or anything. I am a pharmacist by trade and am just trying to learn. I got the camera because I like the option of being able to print large and it is not a large portion of my income. Please feel free to not continue to post back if my skill level/camera cost combination doesn't suit you. All I am saying is the gray card is roughly 1+ stop underexposed compared to metering off the painting and the print seems to confirm that it does not match the original. I have filled frame with gray card and used spot from a greater distance and the metering is the same.

I would be more than happy to read or watch anything regarding exposure, and I have already read lots. The problem is, everything I have read is pretty simple and seems to be what I am doing.

I assume the large gray card in the passport is 18% and that is the value I should be using (I have read some things about 12% being more accurate which would help my case if so). I did purchase the camera used, it is not visibly damaged but how common/possible might it be the meter is broken somehow? Should I shoot the gray card only and look at histogram? It should spike dead center, no?
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BobShaw

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Re: Prints too dark but monitor calibrated
« Reply #30 on: September 09, 2017, 02:29:31 AM »

OK.
There is no large grey card in the passport. There is a very tiny one which is more suited to doing a white balance in post than anything else. A large grey card is 10x8" or so.
However the small one should work. if you are fill the frame with the grey card and set the camera so that the needle is in the middle, that should be correct exposure in manual mode. Ignore the painting reading.
I say should because you could have all sorts of other things set or the meter could be wrong.
And yes, there should be a bar in the middle of the histogram.

Doing that at ISO 100 and f8 indoors is going to be a long exposure. I am assuming that you don't have lights.

One of these will make your life a whole lot easier
https://www.bhphotovideo.com/c/product/1219217-REG/sekonic_401_307_l_308s_u_flashmate_light_meter.html
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #31 on: September 09, 2017, 02:53:47 AM »

I have a pair of lights. Sorry, I meant large in relation to the tiny squares on the other side of the passport. In the first pic below, the side of the passport that is one color, that is 18% gray, right? I will take a pic/crop of just the gray card tomorrow and post the histogram.maybe that will get me somewhere.

I will keep that meter in mind. Thanks!
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farbschlurf

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Re: Prints too dark but monitor calibrated
« Reply #32 on: September 09, 2017, 03:42:49 AM »

Seems you didn't look up the link I gave, so here's the part important for you: (quote from link above from "fantasy photo", want to be correct to mention it's not my own writing!):

For photographers, the reflectivity of an "average" scene is between 12 and 13 percent. So, an 18% gray card would cause under exposure if used directly to set the exposure. But, by holding the card at a 45 degree angle to the camera, the reflectivity of the card would become about 12.7% since the reflectivity changes with the cosine of the angle (cos 45 is about 0.7 and 0.7 times 18 is 12.7). Or, just simple hold the card flat to the camera and then adjust the camera to over expose half a stop from what the reading from the card indicates.

I don't recommend the 45 degree "trick", myself, though, it's prone to failure when there are several lights.

If you have an incident-light meter, this would be the better option.

HTH

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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #33 on: September 09, 2017, 03:50:28 AM »

No, did read it. I just hadn't read the 45 angle anywhere else but I think I determined the problem. As BobShaw I think was trying to get through to me, that card is not 18% gray! I think 18% gray is much darker. If I am not mistaken, by metering off a lighter card, the camera wants to make it darker so underexposes. I just saw that larger gray card and thought it must be an 18% gray. I will remember the 45 angle for smaller tweaks if I need it, though
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BobShaw

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Re: Prints too dark but monitor calibrated
« Reply #34 on: September 09, 2017, 06:18:06 AM »

I have a pair of lights.
That is a whole new world that you have just shared with us.
What sort of lights?
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nirpat89

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Re: Prints too dark but monitor calibrated
« Reply #35 on: September 09, 2017, 07:55:54 AM »

I thought that increasing exposure in post created noise, no? The artist wants the ability to print these large so I prefer not to increase noise.
The answer is No.  Not to any appreciable degree.  Perhaps important if are trying to resolve high-frequency lines on a lens chart.  Not of any consequence to enlargement of an oil painting where the brush strokes will be bigger than the any noise you might introduce with the 645z and 100 ISO.  I think this belief is making thing more complicated for you than it needs to be.

There is no mandate to get the exposure right in the camera.  Only thing you have worry about is there is no clipping of tones in the left side of the histogram, which you do not seem to be doing based on what you shared in your first set of images.  Simply put it in Lightroom and move the histogram to right with whatever knob you want to turn until you get the correct light level.  Print small patches along the way to fine tune. 

If you still want to get is right in the camera, as I said before, set aside your Passport (more trouble than it is worth.)  Use your camera exposure meter in the average mode (not spot mode) take a shot based on that.  Assuming that you are going to underexpose this way for whatever reason, take several more shots reducing the shutter speeds at 1/2 (or a 1/3) stop intervals, until you see the histogram in your camera starts showing clipping on the right side.  I do not know how auto-bracketing works in Pentax, but you can do this without having to manually change the shutter speed.  Now open the shots all in Lightroom and pick the best one. 
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #36 on: September 09, 2017, 09:26:04 AM »

Quote
Quote from: Thenolands on Today at 02:53:47 AM
I have a pair of lights.
That is a whole new world that you have just shared with us.
What sort of lights?

They are not expensive or anything but they seem to be providing even light light coverage...
https://www.bhphotovideo.com/c/product/1008971-REG/impact_ready_cool_2_lighting.html

Thanks for the noise clarification. I don't want to go around shooting 1 stop under all the time but it IS nice to know I can process in post without worrying. Thanks!
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #37 on: September 09, 2017, 01:27:23 PM »

Got gray card (an actual 8x10 18% gray card) and metering is now showing 1/6 second instead of 1/30... that ought to do it!

Thanks for everyone's help. Much appreciated!
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Chris Sanderson

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Re: Prints too dark but monitor calibrated
« Reply #38 on: September 09, 2017, 02:04:54 PM »

The paintings are quite lovely. Don't forget to use your eyes as the best and final judge of the print.

For instance the photo of the sunflowers/blue vase appears quite good but possibly about a stop darker than the original.

Again the use of the Lab readout values on that JPG would inform you of the realtive accuracy of the tones.
The highlight in the plate of your print reads L 83.7, the canvas reads L 93.7 in the same area - that is a 10% difference in Luminance at the top end making your print less bright in the highlights.
The midtones at the centre of the vase read L 46 on the print and L 57 on the canvas. Again the midtone of the print is considerably darker
BUT
The darkest area of the vase on the left reads 18.6 on the print and L 21.0 on the canvas. Only slightly darker in your print
This suggests that the print has 'crushed' the mid to top end a bit but is only very slightly dark at the bottom end.

Please don't interpret these numbers as anything more than a rough guide to what is going on in your print. But it is a lot easier to compare numbers than tonal values by eye on different textured surfaces where at a minimum, reflections can throw things way out.

The 'correct' method is the one that gives you the best result and that will at some stage require your eyes to make the judgment. Lab readout will give a guide but technology does not trump your eyes IMO
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Christopher Sanderson
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Thenolands

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Re: Prints too dark but monitor calibrated
« Reply #39 on: September 09, 2017, 02:25:11 PM »

Yes, Chris, I agree it is slightly dark. That shot was also before use of the gray card. I am reshooting that painting now, in fact, and it did show to decrease shutter speed from 1/8 to 1/6 using gray card vs metering off print so I think that would take care of most of the slight under exposure. Good tip, though, about your eyes being the final check. It is how we are actually viewing the piece, after all.
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