Wednesday , November 21 2018
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Creating a Granite Mural with a Resampled Photo

One of the problems that you have when you are looking at do a mural is typically the photo that you are working with is to small to work with. This was the case when I has creating this mural. For example the photo I was able to retrieve off the Internet was approx. 1.5 inches by 2.5 inches and had a resolution of 300 DPI. Now this is not going to be a big article when it comes to talking about resolution and DPI versus PPI but we will need to spend some time talking about what is the proper PPI to have with a photo. Note: when we look at a photo and we look at its resolution although it is expressed in DPI it really should be expressed in PPI. (which is pixels per inch) DPI is for printing only. As I have already mentioned the original image is 1.5 by 2.5 at 300 DPI. If we take a look at the this granite mural you will see that is 24 inches wide and 36 inches high. If i just resized the original image to this size it would never even come close to engraving properly. For this reason we need to get the photo up to a higher PPI so that we can print it properly. What I am shooting for here is a photo that is 24 by 36 and a PPI of 300. Although I do not have to have it at 300 PPI because I am making it so big if I leave it at 100 it will not process properly when I run it though the unsharp mask and conversion to black and white. Fo this reason I created a photo that had a resolution of 300 PPI at 24 by 36.

Note: If you read this article you will see why you can not just go and buy an off the shelf program and do adjustments in a willy nilly fashion. You would drive yourself bonkers. This is why I recommend that you let Corel do the adjustments and if you want to use an off the shelf conversion program than be careful.

Here is My Finished Mural

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Here is my group of tiles that I used to create my mural

Here Is My Original Image

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Here is my image I downloaded off the Internet. It looks alright from this level but if you zoom in on the image you will see that there is a lot of artifacts from the compression to JPEG.

Here is The Original File in Relation to What We Need

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Here is a momentous job here. Our original is in the bottom right hand corner and you can see it in relation to the size it needs to be. It goes to show you what we can get away with when it comes to laser a photo if you think about what you are doing and be careful with reviewing you image at each step.

Resample The Image

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Seeing the Image is very small I need to resample the image up. Select BITMAPS (1) RESAMPLE (2).

Our Image Statistics

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Here are the characteristics of my image. The width is 1.8 by 2.7 (1). My PPI is 300 (2). This is a break as my image has a higher PPI than most Internet Jpegs which are typically 72 PPI. My file size is 1.26 (3). I have also unchecked “Anti Alias” as this should never be on unless you are creating images for a monitor such as a web page.

Increase The Size of The Photo

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If I increase the width of the image (1) to 24 my height (2) is not enough (2)

Increase the Height

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So instead let us increase the height of the image to our required size which is 36 (1). Our Width will size up to 24.75 (2) which means we will have to crop the width of the image a bit. This is very important to remember here that we always make our image the size that we want before we do any cropping or conversion. You should not just drag the image bigger as you will probably have issues with quality. Also most images you get do not conform to your final size so you will need to crop them. Finally look at the size of my new image. It has gone from 1.26 MB’s to 229 MB’s (3). That is a huge increase in size. If you have a marginal computer it may chock at that increase in size.

We Have Degradation in The Image

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When we blow up this image we really start to see the issues you get with compressed Jpegs which is why if I can get the originals I always will. The green arrow shows my image has become quick blocky. The red arrow indicates that the amount of artifacts is a lot more pronounced now than it was in the smaller sized image. These two issues will cause some real issues when we start to adjust them. We will need to be careful with what we do.

Crop Our Image

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We need to crop our image so that we can get it to the desired size that we need – in this case 24 by 36. We have the 36 but we need to get the width down to 24 inches from 24.75. Select the Crop tool (1) if it is not there let the flyout come out and select it (2).

Draw A Crop Box

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Draw a box so that it encompasses your crop area. Do not worry about the size.

Adjust Your Crop Box

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Adjust you crop box so that it is 24 by 36 (1). Move your photo so that it will be cropped. Make sure that the photo is still inside the crop box.

Check Your Image SIze

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I have checked my image size and it is 24 by 36 (1).

Convert Your Image to Gray

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Convert your image to grayscale by going to BITMAPS (1) | MODE (2) | GRAYSCALE (3).

Here Is Our Image in Grayscale

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Here is my image in grayscale. For me it is a little to dark and it needs to be lightened up.

Open Up Contrast Enhancement

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We need to lighten up the image a bit so we will use the Contrast Enhancement. Got to EFFECTS (1) ADJUST (2) CONTRAST (3).

Adjust the Image Lighter

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Here is our image opened up in the Contrast Enhancement Tool. Our Original image is on the left (1). Our Preview Image is in the right (2). If you look into the histogram area you will notice that the spatial concentration of pixels is skewed to the left or the dark tones instead of the lighter tones (3). This confirms my assumption that the image was to dark. Move your right side slider (green box) to the left from the right. This moves the spatial concentration towards the lighter tones. This makes the image a bit lighter and increases our tonal value of our image (4). This is always good. Note to be able to preview your adjustments click on the Lock tool (5).

My Image is Lightened Up

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Here is my image. To me a little more dramatic in its depth.

Select the Unsharp Mask

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Our Next Step is to Sharpen our image. Go to BITMAPS (1) SHARPEN (2) UNSHARP MASK (3)

Sharpen the Image

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We are in the Unsharp mask tool. I am using the settings I would probably use for black granite a percentage of 500 (1) and a radius of 10 (2)

We Have an Issue

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If we zoom in on this image you will see that it has become very blocky and if we laser engrave this it will not be very good. Ok I could probably spend a day on taking about what is going on here and pull a bunch of examples but the thing to remember is that sharpening although it is always recommended as an enhancement tool can also go the other way and enhance a very pixelated image. So the rule is to always zoom in on your image to check it out. This may not have been to bad at a small 4 by 4 tile but this is not what we are making so the littlest issue becomes more pronounced.

Use a Smaller Adjustment

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To lessen the degree of exaggeration of the photos issues I used a smaller Percentage (1) of 223 and a radius of 3 (2). The radius causes more of the issues with this photo.

Here is My Image Adjusted

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As you can see my image has less issues now. I would have liked to have sharpened it a more but I could not risk the issues in image quality.

Convert Your Image to Black and White

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I need to convert my image to Black and White using our standard error diffusion. Go to BITMAPS (1) MODE (2) BLACK AND WHITE (3).

Use Jarvis

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I have used the Jarvis algorithm for this photo.

My Finished Image

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Here is my finished image.

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