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Old 02-27-2005, 01:27 AM   #1
Garth Herrick Garth Herrick is offline
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Checking Drawing Accuracy in Photoshop




NOTE: This is from the thread Something about Genevieve , started by Jenni Nolen in the Pastel Critiques section. I did a digital analysis of her portrait which I think may be of general interest to all who use Photoshop to prepare reference images or need to check their portrait's accuracy, while in progress.

Always something new to learn in Photoshop!

As it happens, I just learned this new technique with the line tool, in Photoshop, with this digital demo. I measured both the photo and pastel from the chin to the eye. Then with a calculator I matched them both in scale. Overlaying the photo over the pastel in the best possible registration, I drew in the guidelines over the photo, then hid the photo layer to show the lines over the pastel. It's neat!

Garth

Quote:
Originally Posted by Julie Deane
How do you do it?

Garth -

Would you mind telling us Photoshop learners how you do those overlays step by step?
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Your Photoshop secret tutorial directions

Hi Julie,

It's not rocket science and once you get the hang of it, it's a lot easier and intuitive than it sounds.

Here goes:

1.) Download both desired source images the Forum artist has posted. I find I need to rename the images (any name that works for you), and specify ".jpg", in order to get the image to save as a usable file.

2.) Once downloaded, I open both files at once in Photoshop by dragging them together from my Finder window (I'm using a MAC! PC users find your own way.) onto the Photoshop icon in my Dock.

Both images should simultaneously open in Photoshop as two separate files.

3.) Under IMAGE SIZE, I immediately scale these two files to about twice their original size, maybe larger, for ease of use and precision.

OPTIONAL: For convenience, convert in PREFERENCES the measurement units to PIXELS (rather than INCHES or CM).

4.) Using the MEASURING tool (it's buried as an option under the EYE-DROPPER tool in the tool menu at the left), choose something to measure that works correspondingly in both images.

In this case I measured from the bottom of the chin to the middle of the right eye.

Click and hold down the mouse button at the start point of the measurement, and drag it to the end point, and release the button.

In the top menu, following "D:" ,will be the desired measurement readout, in this case, in pixel units. Write down the measurement result, and take the same corresponding measurement on the other source image and write down that result too.

Chances are these two numbers are not the same (if they are you've hit the jackpot and can skip the next few steps!).

Now you will want to match the scale of one image to the other:

5.) Decide which of the two source images you will now modify in scale to match the other. You will either be enlarging or reducing it.

Knowing which way you are going, use a calculator to divide the one written measurement result by the other.
If ENLARGING: divide the larger number by the smaller one.
If REDUCING: divide the smaller number by the larger one.

With the calculated resulting ratio, go to IMAGE SIZE again and pick any dimension listed, and multiply that number by the RATIO you just calculated.

With this next result on the calculator, go back to IMAGE SIZE and replace the dimension used for the last calculation with your new result, by typing it in to the (highlighted) box. Press SAVE and.....Voila!...... Both images will match in scale exactly.

6.) Now you want to copy and paste the one image over the other one.

Choose SELECT ALL to select all the image to be copied. Under EDIT, select COPY, and you will have copied the image to your virtual clipboard.

Going over to your other image that is to receive the overlay, select EDIT/PASTE, and you will now have successfully pasted the one image opaquely over the other, in a new layer.

Now you can edit the opacity of the overlaying layer, in the LAYER menu to the right. It will initiall read 100% in the numerical box. Click the small arrow to the right, and a slidebar will appear to allow you to modify this opacity setting to that which you desire, say 50% for now.

Now you can see both images about 50/50 apiece overlaid. With the MOVE tool in the left side tool palette, drag this top layer over the background layer until you register a good match (in this example we are matching both right eyes until they perfectly coincide and register as one). Ideally you will now see most features manifest in their perfection or imperfection, superimposed.

7.) Now go back to the LAYERS menu and reset the opacity back to 100%.

Important OPTION if you are painting lines with a BRUSH: Open a new LAYER/NEW/LAYER. This will be called LAYER 2. You can draw with the BRUSH any outlines or key registration points you wish onto this overlaying layer.

If you use the LINE tool (as I did), every straight line segment you add will automatically generate it's own separate LAYER! I generated over 50 more layers with all these angular connecting lines!

Above all, remember that the pasted in image layer is called LAYER 1. You will later be going back to it. All the added line segment layers will be LAYER 2, 3, 4, etc,......

With a BRUSH or LINE tool, whichever method you are comfortable with, draw some outlines around the key features you want to compare.

8.) Going to LAYER 1, select it and toggling the EYEBALL icon to it's left, you will hide that layer from view, revealing the other background source image and the verity or inaccuracy of it as evidenced by the colored outlines you just drew and overlaid.

9.) LAYERS/FLATTEN this image (you will discard the hidden layer, for now). FILE/SAVE AS this file as a new name, whatever works for you.

This is the saved image that will show all the errors and inaccuracies.

10.) In HISTORY, back up a step or two, to the historic state in the process just prior to when you hid LAYER 1. Select that point of history, and you will be back where you were earlier with all the multiple layers.

11.) Now once again, do the LAYERS/FLATTEN to the image in this state. Now once again, FILE/SAVE AS with a separate distinct file name.

This is your other saved image that shows the guiding painted lines in total agreement with the image, because this is the image you used to draw those lines.

12.) Resize and SAVE AS both these saved files to the sizes and standards needed for posting back in the FORUM, Post and upload the images, and write your descriptive justifying blurb, and you're Done!

When all this is second nature it can be accomplished in a matter of a few minutes of your time. It's not really that big of a deal.


I hope this helps!!!

Garth


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Old 02-27-2005, 04:13 AM   #2
Allan Rahbek Allan Rahbek is offline
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Garth,
thank you for taking your time to explain this process. One less dumb question to ask for me

Allan
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Old 02-27-2005, 08:29 AM   #3
Julie Deane Julie Deane is offline
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Thanks so much!

Hi Garth -

As I said in the other posting, it may not take long to do, but it took you a long time to give the written instructions. Thank you for your willingness to do this for us!
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Old 02-27-2005, 11:01 AM   #4
Carol Norton Carol Norton is offline
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Photoshop Elements 2.0

THANK YOU, Garth, for that step-by-step lesson. My one remaining question is about Photoshop. I bought Photoshop Elements 2.0 for my Mac. Will all those steps work on this less expensive program?
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Old 02-27-2005, 11:50 AM   #5
Garth Herrick Garth Herrick is offline
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Quote:
Originally Posted by Carol Norton
THANK YOU, Garth, for that step-by-step lesson. My one remaining question is about Photoshop. I bought Photoshop Elements 2.0 for my Mac. Will all those steps work on this less expensive program?
Carol Norton
Carol.

I have no experience or idea about Photoshop Elements 2.0. My wife has it on her Mac, and when I looked at it I did not understand it's navigational setup at ALL! I'm only fluent in Photoshop CS, it seems!

Someone else will have to transpose instructions, if possible, for PS Elements, because I don't really have access to it, to learn it.

I believe some of the navigational paths I describe would be significantly altered. There may be some built in limitations, reserved for the more robust and professional PS CS. I just don't know.

Good luck, let us know what you can discover regarding this.

Garth
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Old 02-27-2005, 10:10 PM   #6
Denise Hall Denise Hall is offline
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Garth,

I want to thank you also for giving your time to do this - I needed it - just ask Beth!! You are such an inspiration around here too - and here's a chance for me to thank you for sharing all your beautiful work with us too.

Denise
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Old 02-28-2005, 11:22 PM   #7
Elizabeth Schott Elizabeth Schott is offline
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Whew Garth, that was a mouth full, very nice of you to walk through all these steps.

I kind of skimmed since I am aware of this, but I wanted to point out just a few things that maybe you can tell me are correct or not.

If your image of your canvas is just a bit eschewed it will distort and give your outline check a bit of an "off" reading, so you need to take care in photographing your painting.

Also does it work the same if you don't use the calculator but just paste the image into an exisiting file (like your reference) which makes a new layer then sizing them the way you talk about with the opacity at 50 so you can see if it's the same?

Julie Photoshop Elements 2.0 does do all of this, it's really pretty close to full Photoshop CS, except when it comes to any pre press type features, or things most of us wouldn't even think about.
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Old 03-01-2005, 12:03 AM   #8
Garth Herrick Garth Herrick is offline
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Hi Beth,

Good post questions!

You are correct to point out that one needs to take care to not have skewed or keystoned images, or the test drawing in the overlay will give false results. That is a whole another chapter to explain how to correct skew, aspect ratio, or keystone/perspective distortions. One of us should take the time to do that though. This is not rocket science either. As I just pointed out in another current thread about photographing paintings, I routinely take skewed pictures of my paintings (to avoid head-on glare), and then I remove the distortions in Photoshop (EDIT/TRANSFORM/DISTORT).

Beth if you can find a shortcut that does not use the calculator step, by all means share it with us! I know that one can change the scale of the overlay layer in EDIT/TRANSFORM/SCALE, but I have not seen how it is possible to constrain proportions in the process. If there is a way, then show me.

Thanks for resolving the question about PS Elements 2.0.

Garth
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Old 03-01-2005, 12:30 AM   #9
Elizabeth Schott Elizabeth Schott is offline
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Quote:
That is a whole another chapter to explain how to correct skew, aspect ratio, or keystone/perspective distortions.
HA! Garth, now you are going to need to spend even greater amounts of time to teach me this!

Quote:
Beth if you can find a shortcut that does not use the calculator step, by all means share it with us! I know that one can change the scale of the overlay layer in EDIT/TRANSFORM/SCALE, but I have not seen how it is possible to constrain proportions in the process.
I must qualify the fact that I have no idea if this is correct, but it is what I do. Instead of all the calculations, you just make sure the two images you will be working with are the same resolution - dpi, before you paste one into the other, then just use the transform/scale feature.

Another trick is to take your reference and do a "path" out line of what you need to highlight, save the path. Then open your file of the painting and with them both open - just drag the saved path from the reference on top of the painting file and it will be saved there too. With the path tool selected (the pen or arrow just above) you will have an option to use the transform path/scale feature. Scale your path as needed and whammo, there's the mistakes or perhaps the perfection you were hoping for!
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Old 03-01-2005, 12:40 AM   #10
Garth Herrick Garth Herrick is offline
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Quote:
Originally Posted by Elizabeth Schott

Another trick is to take your reference and do a "path" out line of what you need to highlight, save the path. Then open your file of the painting and with them both open - just drag the saved path from the reference on top of the painting file and it will be saved there too. With the path tool selected (the pen or arrow just above) you will have an option to use the transform path/scale feature. Scale your path as needed and whammo, there's the mistakes or perhaps the perfection you were hoping for!
Beth,

Please expand upon your "Path" method. I have never delved there before. (I want the ten page step-by-step instructions!)

Garth
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