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Simulation of film contrast, brightness, and color masking in Photoshop


littletank

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Many years ago I came across a way of improving certain colour slides and I am wondering if it would be possible to replicate this procedure using Photoshop. The method required making a negative copy of the slide using orthochromatic film and then sandwiching slide and negative together. I suppose one could have used lithographic film but not panchromatic film.

I have a feeling that it should be possible but my knowledge of Photoshop is not very extensive. I would be delighted if anyone could help solve this puzzle.
 

Tom Mann

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What you are describing is an old, but classic method for contrast control.

A variant of this is to blur the negative version a bit, and reduce its contrast, and you have another classic technique called "unsharp masking".

Lots have been written about both techniques. Just Google {sandwich negative with transparency control contrast} to learn about the first.

Take a look at http://www.largeformatphotography.info/unsharp/ to learn about the second.

These days, it is the opinion of almost every experienced photographer that these techniques are superannuated and no longer needed because the goals of these techniques can be achieved with even better results and vastly more flexibility using purely digital means.

Why don't you post an image that you think could profit from the first technique and we'll be happy to illustrate how to essentially do the same thing in PS.

Cheers,

Tom M
 
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Tom Mann

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PS - I'm going to move this thread to the "Post Processing" section of the photography forum. I'm also going to give it a more descriptive title. You should be redirected there automatically.

Cheers,

Tom M
 

littletank

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Thank you for your reply Tom, but I do understand how to control contrast and sharpen using Photoshop what I am describing is neither of these. Forgive me if I am teaching my grandmother to suck eggs but making a copy of a colour slide onto orthochromatic film or lithographic film does not copy all the colours and this, I believe, is significant.
 

Tom Mann

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You're right, the differences are significant.

Take a look at the details in Norm's article, particularly, this section:

The technique is as follows.

* Click on Layer, Duplicate Layer or Right-click on the image name in the Layers palette and select Duplicate Layer. Give the new layer a distinct name like Contrast mask.
* Select the new layer and click on Image, Adjust, Desaturate to make it into a grayscale image.
* Click on Image, Adjust, Invert to create a negative of the grayscale image.
*In the Layers palette, set the box on the upper left (Blending mode in Layer, Layer style, Blending Options) to Overlay. Set Opacity to about 80%. You can fine tune it later. (Michael and Uwe differ in the order and details of this step.)
*Click on Filter, Blur, Gaussian Blur to blur the mask layer. Adjust Radiusfor the desired effect, which will be visible. A good starting point is 1% of the average image dimension in pixels (e.g., 25 for a 2000x3000 pixel image). Values between 10 and 100 are typical.


The step where he simply desaturates the image can be replaced with the use of PS's "black and white" adjustment layer to approximate the differences between pano, ortho and other spectral responses.

HTH,

Tom M
 

Tom Mann

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PS - I'm going out for several hours, but will be back later. I'd love to continue this discussion then.

All the best,

Tom M
 

littletank

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Perhaps I haven't explained myself very well so I will try again. Firstly, I am not concerned with sharpness but with colour, if that's the same as contrast then so be it. Secondly, visualise what happens when a colour transparency and a piece of non-panchromatic film are placed together with the sensitive layer of film in contact with the transparency, white light shone through the transparency and the film then developed, fixed, washed, dried and examined. What do you expect to see?

If you hold the piece of film in front of a white light you will see a negative image of the transparency varying from opaque to clear, transparent film. Blue will appear to be black, red will be clear film and all the other colours will be in various shades of grey. Now, sandwich the colour transparency and the monochrome negative piece of film together and project the image using white light, that is what I would like to replicate.

Would it be possible to replicate the negative image as a mask?

I hope you enjoyed your outing and I too look forward to continuing the discussion.
 

Tom Mann

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I'm home for a few minutes between honey-do errands, so this is going to have to be terse.

a) I completely understand that you are only interested in changes in brightness/contrast, not sharpness.

b) I also completely understand and agree with your statement, "Blue will appear to be black, red will be clear film and all the other colours will be in various shades of grey. Now, sandwich the colour transparency and the monochrome negative piece of film together and project the image using white light, that is what I would like to replicate.". In other words, when projected, blues will be darkened, if not completely black, reds will be untouched, etc. etc.

c) As an example, I'm going to use one of my images that has strong colors: a red fire truck, a nice blue crisp September sky, a yellow line on the street, green street sign & trees, etc.

D7C_3481-demo_of_ortho_pano_litho_sensitivity-ps01a-01_original_colors.jpg

Later, when I return, I will simulate using a very high contrast emulsion that has only blue sensitivity to photograph this scene, and then, a digital simulation of the sandwiching of the negative with the original tranny scene.

Sorry, gotta run...

Tom
 

Tom Mann

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...and just to quickly also include a version of this scene as if it had been photographed using panochromatic (broad spectral sensitivity) negative film.

D7C_3481-demo_of_ortho_pano_litho_sensitivity-ps01a-02_normal_pano_negative.jpg


...and now, with high contrast film that is only sensitive in the blues

D7C_3481-demo_of_ortho_pano_litho_sensitivity-ps02a-03-blue_sensitive_negative.jpg
 

Tom Mann

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And finally, a digital simulation of the sandwich using the linear burn layer blending mode in PS of the previous image with the original.

D7C_3481-demo_of_ortho_pano_litho_sensitivity-ps02a-04_sandwich_simulation.jpg

I believe that this is something like what you were looking for.

This version is quite garish because for this example, I simulated a very high contrast negative blue-only emulsion, whereas for real work, one would use lower contrast, a more gentle transition between the blues and the rest of the spectrum, etc.

Now, I *really* have to run.

More later,

Tom
 

littletank

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That looks exactly the sort of thing I had in mind especially the high contrast film image. I now await with great interest to know how you did it.
 

Tom Mann

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Great. I thought that was what you had in mind. I'll be back on the air, either very, very late tonight or tmmrw AM.

Cheers,

Tom M
 

Tom Mann

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So, here is the layer stack that I used:

00_layer_stack.jpg

At the very bottom is the original color image.

The next layer up from that is a Black & White adjustment layer, one of PS's native tools. The settings I used are shown here:

10-BW_adj_layer_settings.jpg

The idea behind these settings is to simulate a B&W film that only has sensitivity in the blue and a bit of the cyan area of the spectrum. This blows out the sky, which is exactly what we want and is what is on "Layer 1" of my layer stack.

To convert this to a simulation of a high contrast negative, duplicate this layer, hit cntrl-I to invert it, and then use image/adjustments/curves to further increase the contrast. The reason behind this last step is that for the purpose of this demo, we really want to blacken the blue sky and have almost no effect on the other hues, so we want these to come out very white on the simulated negative. The result is shown below (ie, the layer titled, "negative+curves" in the layer stack):

D7C_3481-demo_of_ortho_pano_litho_sensitivity-ps02a-03-blue_sensitive_negative.jpg

At this point, we can simulate clamping the negative to the original. We do this by turning off all the layers between the simulated negative, and changing its blending mode to multiply.

I now hit cntrl-alt-shift-E to make a copy of the result on a new layer at the top of the stack. This is called, "Layer 2" in the layer stack, and is shown below:

40-turn_off_all_all_layers_except_hi_contr_blue_only_negative-and_change_layer_blending_mode_to_.jpg

This is the same as what I posted yesterday afternoon, and used almost exactly the method I summarized in post #6 of this thread.

Obviously, there are many possible ways to tweak this method to needs of any particular image, eg, where you want the sky slightly darkened, but not black.

I feel obliged to add that there are much more direct ways to get effects that are very similar to the above, but the method I described above almost exactly parallels the old school film steps, which is what you requested.

For example, one could simply select the sky (with any of several tools or methods), and apply a "levels" or "curves" transformation to just the sky. A quick & dirty version of this is shown below. Because this wasn't exactly what you were interested in, I did not spend any time accurately masking out the power lines, so they turned black along with the sky. However, on the plus side, the non-sky parts of the image are changed less using this method. This might or might not be to your liking.

D7C_3481-demo_of_ortho_pano_litho_sensitivity-ps04a_darken_sky_using_masked_curves_layer-01.jpg

Finally, to be honest, I have never turned a sky completely black before this. However, once I did, it occurred to me that this might be a quick way to get started with a day-to-night transformation, e.g.

D7C_3481-demo_of_ortho_pano_litho_sensitivity-ps03b_8bpc_night_conversion_possibility-01.jpg

There is lots of fun to be had with these methods.

HTH,

Tom M
 

fredfish

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Fascinating - great process. Thanks for the details.

Cheers

John
 

littletank

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Thank you very much indeed for detailing the method, I'll spend some time trying to get to grips with what is happening and also investigate the effects of different settings. Who knows, something of real interest may result. Any way, it will keep me off the streets.

For the record, could you point me to the forum's limits on image size in case I ever want to post a picture.
 

Tom Mann

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I'm glad the explanation was interesting.

With respect to page limits and the like:

1) One should **ALWAYS** post in sRGB, not Adobe RGB, and certainly not in ProPhoto or any of the CMYK variants. You wouldn't believe the confusion and problems that violating this rule has caused.

2) If you post a JPG that is less than 700 px in its longest dimension, and, as I recall, less than 300 kB in size, it will appear completely unchanged in the in-line forum preview window. This is exactly what you want and is the safest way to post, IMHO. Post above those limits and it will be subjected to the tender but crushing arms of the forum's compressor and you will start to see all sorts of weird JPG, staircasing, halos and other artifacts in the in-line forum mid-sized preview. However, one can still click on this preview and get to the original to download. Unfortunately, lots of people don't do this and incorrectly judge the quality from the in-forum preview.

3) As I recall, the largest JPG that is allowable is 3500 px on the longest dimension. I forget what the maximum file size, but it is at least several megs.

4) PSDs and other file types can also be uploaded. Some of these will be treated correctly by the forum software, others will not. I forget the details. IMHO, the best way to upload non-JPG file types is to zip the file and attempt to upload it as if they was an image. The uploader will protest, but just ignore its comments and forge ahead. It will get uploaded with some comment like, "unknown file type". The advantage to zipping large files is the forum won't be able to tell the dimensions of the image in pixels, so the only limit it imposes is absolute file size. As I recall, this is several tens of megs.

5) Above this size, the best thing to do is upload your image to Dropbox, yoursendit.com or any of the other free, no-signup-required file sharing services, get the URL and post the URL in the forum thread.

There is an actual FAQ discussing these limits somewhere, but I have to run out again and just don't have time to link to it. Hopefully, someone else will do so before I return late this afternoon.

Best regards,

Tom M
 

Jerry D

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Hello littletank

Some info on image attachments is here and here

There may be more but I haven't read everything on this board....yet.
 

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