Correcting underexposure in PhotoShop 6

[linc]

Like an idiot, I failed to realize that the automatic detection of

ISO had been disabled on my Nikon after it came back from the shop.

 

I inadvertently exposed a roll of Velvia film at 200 ISO, but I did

not discover the error until the film was developed. [Otherwise, I

could have asked the camera shop to treat the development as if it

were pushed two stops.]

 

What I need to do now is use Photoshop to correct the problem. I

could hunt and peck at the menus until I found what needed to be done-

--brightness, saturation, etc.--but maybe somebody out there has

already found the solution.

 

If so, help!!!

 

Linc Wolverton

[ellis_vener_photography]

go to Image > curves and start by pushing the middle of the composite RGB

curve towards the top. Good luck you are at least two stops underexposed.

[emre]

I doubt the film holds any usable information. At any rate you would need a drum scanner to salvage it. Try Levels and pull the middle slider to the left. If you are doing your own scanning, this is a textbook case of when to increase the analog gain--do it if possible! Finally, please post an example.

[ellis_vener_photography]

Do not use levels use curves. Using Levels throws away big chunks of data,

and you are going to need all the data you can get your mitts on.

[thomas_van_dyke]

Linc;

 

The preceding answers are indeed valid if you have a reasonable working knowledge of Photoshop. And Curves would be even better, but if you knew how to use Curves you would not have asked the question. Therefore I assume you are new to Photoshop version 6. When coaching newbies in the application I like to take them to the Menu choice; Image; Adjust; Variations so they might be able to use some of the incredible power latent within this application visually (and without spending countless hours mastering the details of levels and curves). Try it and see�

 

Purist may flame this counsel as "bad, you should use visual crutches" however the sad truth of the matter is that countless folks give up the application owing to it's complexity. It does need to be this way; Adobe has built into the application a host of �bicycle training wheels�. I would like to plead with the more advanced users to help other newbies along. We all were puppies once... Cheers;

[noshir_patel]

This is not the time to use photoshop at all but to use your scanner software. Scan with analog gain cranked up (if your scanner supports it) and adjust levels or curves within the scanner software. This way you get the best the scanner can give you. If you do it in photoshop, the scanner has already thrown away a lot of potentially useful bits.

 

On the other hand, two stop underexposed Velvia is likely unrecoverable (at least if you want any level of quality).

[chris russ]

You might also consider scanning the image more than once and adding the images together. At least you can eliminate noise that comes from the scanner (which is not insignificant, especially in the blue channel in dark images). You rapidly reach the point of diminishing returns, but 4 scans should add a whole bit (factor of 2) to the S/N of what comes out of the scanner.

[emre]

<i>Using Levels throws away big chunks of data...</i>

<p>In theory, this is not true--Levels is merely a special case of Curves (when you constrain "the curve" to be the Gamma function). In practice though, you may be right if <a href="http://www.aim-dtp.net/aim/evaluation/gamma_error/main.htm">there is a bug in the implementation</a> (more <a href="http://www.aim-dtp.net/aim/photoshop/v5/slope_limiting.htm">here</a> and <a href="http://www.lumika.org/gear_nikon_scan_vs_photoshop.htm">here</a>)...

[k_t4]

I respectfully disagree with Noshir Patel's response in this thread. It is important to understand the difference between controls in scanner software that pertain to scanner functions and controls in scanner software that pertain to image editing functions. Analogue gain (in NikonScan) or RGB Exposure (in VueScan) for example are controls that do indeed control the scanner and influence the raw data that results in the analogue to digital conversion. Controls in scanner software like Curves, Levels, Brightness, Color Balance, etc., are image editing tools that are applied to the raw digital data after the scan has occured. They are image editing tools. They may differ in their functionality and user interface design, but they are essentially no different than using Photoshop or any other image editing application.

 

The unfortunate aspect of this is that many people are not aware that they are actually degrading the data of their scan when they perform image editing in the scanner software, just as they would in Photoshop. If your scanner software allows editing in 16,14,12 or 10 bit but only allows output in 8 bit, (like Silverfast Ai) then there is a benefit to doing as much editing as possible in the scanner software. If you can output 16 bit files (like VueScan) then the decision on where to do your image editing is largely a matter of workflow and personal preference.

 

Concerning Linc Wolverton's original inquiry, it is of course important to make sure the raw scan is optimized. The scanner software/scanner hardware combination determines what options you have to control this. Without knowing this I can't make a recommendation.

 

I'd also suggest looking at some of the Photoshop tutorials listed at http://www.luminous-landscape.com/subject_index.shtml - There are some basic tutorials as well as some more intermediate procedures. Take a look at "contrast masking" for instance. Many of the best solutions for a problem like yours are fairly involved, and many images are simply not recoverable (GIGO). In the end there is no substitute for taking the time to search out and experiment with Photoshop techniques to handle problem images. Tutorials abound on the web. A good book will also help you with this.

[linc]

Thanks for all the input to date.

 

In response to Kevin Thurner's note, I scan the slides with an LS-2000 machine running under Nikon's 3.1 scanning software. I have analog gain set to neutral, Digital Ice se to normal, 16X passes and 8 bit output.

 

I normally control the scanner through the Photoshop 6.02 Import command--just pressing the buttons to scan.

 

As soon as I have the time to scan in one of the photos as an example, I will do so, and upload it.

 

Linc W.