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Archive for the ‘image resolution’ Category

Photo restoration and matching grain for photo repairs

This is a follow on post from my original matching grain article a while ago.

This is just one example of how to match grain when replacing a back ground or perhaps any part of an image.

matching grain strating image

Look at this image, it is part of a man’s shoulder and the background could do with evening out or replacing altogether.

matching grain delete and fill

Here I have just selected and deleted the back ground to white. It does not look at all right.

matching grain blur

Above a blur might clean up the background. Whilst evening out the background it still does not match very well.

matching grain blur and add grain

Here I have added some grain (noise) but it still does not match. If I apply a blur to this then we can achieve a better result.

matching grain blur and add grain and blur

With a slight blur its much better and using the correct selection technique for the original background selection it looks fairly convincing. Using this matching grain technique and varying the amounts of grain and blur ratios and perhaps even repeating the process a few times along with varying the type of noise, we can achieve different  patterns of grain to suit nearly every situation.

For a short video on this topic see below.

I am not an advocate or you “must replace the background”. In fact i’m quite the opposite. The above is meant to show you what can be done if its needed.

Photo Restoration and Image Resolution – Part Two.

The simple printing rule.

After your Photo Restoration is complete, scale you image across the page at somewhere between 250 to 300 pixels per inch to give you an optimum print. If you need to go bigger then just scale to 200 pixels per inch or even less. Do a test and see how it looks. If it looks good go for it.

When you set your printer going set to maximum resolution and use the best paper you can afford.

NOTE: Don’t get confused again with the maximum resolution of your printer being 4800 x 2400 dpi as this is just how much ink going down on the page used to print those 300 pixels per inch you scaled across the page earlier.

The continuing conundrum

I often speak to printers who tell me they need a large file size in order to print to a predetermined size. It is cast into the conversation “ it must be at least 18mb”. When asked why, the response is more often than not because I need it big to work with I know what I can do with a large file. My point I try to make is that I can make you a large file if you wish but do you actually need it. A typical TIFF of a 6 mega pixel image is 17MB. Anyway the print houses want large files but we can make them larger but the dimensions will remain the same so how will they benefit by having a larger file. If we convert the file to 16bit per channel in Photoshop the file size will swell enormously as the colour information contained in the image is now so much greater. I’m am certain that this will not benefit the printers in anyway as they still have the same 6 million pixel image we started with but a file size up in the 34mb region, then if we convert to CMYK it reaches a massive 46mb !!

Here is a break down of how this worked

6 MPixel 2816 x 2120 1.7 mb JPG 8 Bit/channel RGB
6 MPixel 2816 x 2120 17 mb TIFF 8 Bit/channel RGB
6 MPixel 2816 x 2120 35 mb TIFF 16 Bit/channel RGB
6 MPixel 2816 x 2120 46mb TIFF 16 Bit/channel CMYK

Photoshop converted the 16bit per channel. This was completely unnecessary but done to illustrate a point that a large file can be obtained fro 1.7mb JPG. Most software’s (in fact I don’t know of any) can’t edit a 16 bit per channel image, as there is just too much information to process, It is normally converted to an 8 bit per channel image 8 RED + 8 GREEN + 8 BLUE = 24 bit colour for RGB or 32 bit colour for CMYK which can then be processed by most editing software’s. For an explanation of bit depth see below.

Bit-Depth (Scanner used as an example)

Bit-depth refers to the amount of information scanner is capable of recording per pixel. A 1-bit scanner can only express one of two values per pixel: solid black or solid white. For a capture device to reproduce the grey values between black and white, it must be able to record at least 4 bits of data per pixel, which is equal to 16 possible combinations of black and white, or tones (4 x 4 = 16). To reproduce continuous-tone images, such as black-and-white photographs, a scanner must be able to record at least 8 bits per pixel, or 256 possible tones (16 x 16 = 256). While an 8-bit scanner might be satisfactory for black-and-white images, you’ll need three times as much information to record colour images. For example, you’ll need at least 8 bits for each of the three primary scanning colours — red, green, and blue — giving you a total of 24 bits per pixel (8 + 8 + 8 = 24). If you factor the total number of colours that can be recorded by a 24-bit scanner (2 to the 24th power), you’ll come up with approximately 16.7 million colours, more than can be perceived by the human eye. Therefore, a 24-bit scanner is usually considered adequate (but minimum) for most colour scanning.

Most scanners on the market offer 30- or 36-bit colour, which is more colour information than is considered necessary (and more information than most consumer imaging software programs can process). However, there are advantages to scanning images at a higher bit-depth, such as providing a larger pool of tonal information from which to draw. For example, a scanner’s CCD rarely provides you with 100 percent high-quality data from a scan. Some of the data is going to be corrupted by noise or scanning artefacts. Scanning at a higher bit-depth enables the scanner software to choose the best 24 bits of colour, and discard any unwanted pixels that might degrade the quality of the image. This is best done by the scanner software during the pre-scan phase of the operation.

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Image Resolution – (the important part before any Photo restoration can begin)

Image Resolution and photo restoration. Part 1/2

Before we start restoring any photographs we really need to understand printing resolution so we know how big our final photo restoration can be printed

The amount of times I have received requests for information on the ins and outs of printing resolution. I have read many an articles and to be frank none of the put it very simply. Here is my version.

You own a printer and you own a digital camera or have some digital images you wish to print. Just how big can you print and it still look good? Well it amounts to several factors but the best one is whatever looks good to you. This sounds very amateurish and am sure some of you might wince at my short answer, but really if you are happy with the result then that’s an important factor. But if you are not happy then maybe you are viewing it too close, viewing distance is also another factor. Seriously do you look at an A3 picture from 10 inches away or do you stand back and admire the picture for what it is? You should view it from a distance that is right for the size of image. If you are too close then you may see the digital artefacts or pixels that the image is made up from, this is most likely to happen on larger photos than 10×8 inches or on posters.

Ink Jet printers often have an enormous printing resolution, for example 4800x 2400 dpi, dots per inch. You can immediately get confused if you try and equate this with the resolution of your image, for example your cameras resolution is 2816 x 2120 or 6 million pixels. If you print the image using the printers maximum resolution, then surely your image will appear less than an inch big? Yes, but this is not how you should interpret it, you cannot literally equate the two devices in this way, I will explain

Commercial printers who uses printing presses used to publish books or glossy magazines always request images at 300dpi as that is the industry standard. This is a good optimum printing resolution for us too, and this can be used as a base for our printing equation. Simply put, what ever your image is in size it can be printed at 300 dpi. Well actually its ppi or pixels per inch, as you camera or image is digital and in pixels, not dots like a printer. For example even a 640 x 480 resolution image can be 300 dpi but will only measure just over 2 x 1 inches achieved by simply dividing the dots per inch into the pixel size of the image. When we get larger images such as 2816 x 2120 we can see that at the optimum printing resolution of 300 dpi. We spread those pixels over 300 pixels per inch and get a image size on paper of 9.4 x 7 inches.

see more in part two…

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