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Gary_Yngve

Digital Photo Tips

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I've had requests from time to time for advice on how to process digital photos, so I'll write about them here. Please keep this thread spray-free.

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First, some jargon. Pixel count, physical size, resolution...

dpi, ppi...

 

The link below describes things well.

 

http://www.photo.net/learn/resize/

 

Basically, when displaying on a screen, only pixel dimensions matter. Most monitors these days have resolutions somewhere between 800x600 and 1600x1200.

1600x1200 is about 2 megapixels.

 

For printing, you want a higher pixels-per-inch than the ppi on a monitor (around 72 ppi). Probably upward of 180 or 360 . You'll need higher megapixels for better printing. For example, a 16"x12" print at 144 ppi would need 4 megapixels, and the same size print at 180 dpi would need 6 megapixels.

 

So now the questions...

what size/compression/settings do I use for the camera?

what size/compression/settings do I use for web images?

what size/compression/settings do I use for printing?

 

More on these later...

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1) What size/compression/settings do I use for the camera?

I recommend taking pictures on max settings. Largest non-interpolated resolution, highest quality jpg compression. Unless you know what you're doing, you probably don't need RAW or Uncompressed. My reasoning for this is you don't want to regret not having better data later.

 

What about space? The good news is you can now find 1G Flash cards for $20 or so if you look in the right place. That's a lot of pictures. Need more harddrive space? You can find 250G harddrives for under $100, perhaps even with enclosures (so you can carry them from computer to computer and not have to open anything up).

 

2) What size/compression/settings do I use for web images?

The most important thing is to get the images to the right size. A 6MP image won't fit onto anyone's screen. For photos on an online essay, you probably want them smaller than the screensize. Remember that other frames of the webpage also take up screen real-estate.

 

An inset image can probably be around 320x240, and a thumbnail around 160x120. A fullish-screen image around 800x600. If you're writing html code and set the size of the image in the code, beware that if you're not careful, the user could be downloading a large 1600x1200 image that's just going to be squished into 160x120.

 

For quality, around 75% should be good, unless you're trying to get flawless results. Less than 75% may introduce blocky or noisy artifacts or banding (when colors don't transition smoothly).

 

Also, if you're emailing pictures as attachments, many email services don't allow more than a few megs to go through.

 

3) What size/compression/settings do I use for printing?

 

The important part here is to set the pixels per inch or otherwise tell what physical size you want the print. Use your original image dimensions. The printer will take care of the rest.

 

One thing that does come up with printing is how it looks on the screen vs paper. Sometimes there are issues with brightness or color casts. A trick I do is I print the image (or several) really small (and not on my best paper) and look at them, perhaps doing more than one pass of adjusting colors. That saves paper and ink.

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Good software to use:

 

Irfanview - free

- does resizing, sharpening, saturation, etc.

- does batch-style processing for lots of images at once

- not the best interaction

 

Photoshop - pricy

- does most anything you'd ever want

- very interactive, great undo capabilities

 

Common operations in both:

Gamma (sliding mid-gray around in Levels for Photoshop):

Adjusting gamma brightens or darkens the image as if the exposure time had changed. This is different from a "brightness" adjustment, which gives a worse result (linear adjustment). Gamma won't be able to salvage anything that's completely over/underexposed, but it works well. <1 goes darker, >1 goes brighter. Be careful to take into account the brightness of your monitor and the surrounding light in the room when deciding on the right gamma.

 

Saturation:

Saturation enhances the richness of the colors. If you saturate too much, the colors will lose their smoothness and look bad. In general, I find that digital cameras undersaturate their images.

 

Contrast (also by sliding black & white in Levels in Pshop):

Exaggerates subtle shade differences - makes the darks darker, and the brights brighter.

 

Unsaturate (monochrome):

Makes the image B&W. To go Sepia, you can then pump up the red channel by a gamma of 1.1 and the green by 1.05.

 

Sharpen:

Sharpens the image.

 

Unsharpen:

This actually sharpens the image by producing a difference image that contains the high-frequency components and adds it back in.

 

For both of these, be on the lookout for making the image too sharp. Look at hard edges and make sure there is not a halo forming around it. Also make sure that the image isn't becoming too noisy from the noise getting sharpened.

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Photoshop-specific tools:

 

Autolevels:

Sometimes this helps, sometimes it doesn't. Often on images, I try it and undo it if I don't like it. It's really quick to test. (ctrl-shift L, ctrl-Z)

Autolevels can be nice and remove the blue cast from snow on cloudy days, but it may also remove alpenglow.

 

Match colors:

This is a really neat tool that's pretty hidden. Click neutralize, and watch how it tries to remove the color cast. You can use the slider to adjust how much to remove. Often for the blue casts, I keep only 25% of the original blue.

 

Layers and blending:

More complicated topic. But you can copy an image into multiple layers, do different things to the different layers, blend them by erasing parts of the layers (with a really large soft eraser brush), and finally flattening the layers into one image.

 

Healing brush, cloning brush:

Great for cleaning up little things: twigs, powerlines, etc.

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I'm only explaining things on a really cursory level and not providing any examples, so please reply if you want more detail or have any questions.

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w00t! I want to be the first to post in the NEW GARY YNGVE PHOTOGRAPHY FORUM

 

rockband.gifrockband.gifrockband.gif

 

good stuff there gary.

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Gary, why don't you totally geekout and tell me what you can do with the images when you shoot in RAW.

rockband.gifGeek_em8.gifrockband.gifGeek_em8.gifrockband.gifGeek_em8.gifrockband.gifGeek_em8.gifrockband.gif

you know you want to

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I've had requests from time to time for advice on how to process digital photos

 

oh you have not

 

Well, I know he has had at least one request, and he has answered my initial questions well. Maybe I can get some of my pictures down to a reasonable size and still good quality and then figure out how to post them here.

 

Thank you Gary.

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This is good info. Thanks for taking the time to put this thread

together Gary. thumbs_up.gif

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I too think this is a good idea for a thread & a good place to have it. There are, of course, any number of dedicated photo sites on the web, but they all seem to lean heavily towards slathering over equipment.

 

When I shot film, in particular when I stuck to one film (Kodachrome) the technical side of things was really pretty simple. Certain lighting could be relied upon to produce good stuff and other lighting guaranteed pretty boring pix, worth taking only if it was the only time you were ever going to be there.

 

The digital medium, both camera and post processing, introduces so many more variables into the works...I'm still strugggling a bit to keep track of them. Consequently I happily devour any and all wisdom about such things that I come across,

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You're not the only one, Neal. I asked for some basic guidelines in a TR thread recently, and Gary came across with some good guidelines. Namely, that the 35K limit mentioned in the FAQ is bushwah. So, thanks again Gary.

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Hey Gary, is there a website that I could download Irfanview? I don't have any photo editing software, but have been thinking about it. So far all the editing I do is on the camera itself, basically downsizing images to send. I don't think I need anything fancy like photoshop.

 

Also my camera has a "fine" setting, what is this used for?

 

I have been thinking about buying an external hard drive for images that I have been collecting since I have been in Rwanda. Any suggestion on where to go to get one, who has the best prices?

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Hey, Gary, question for you.

 

Infranview has many filters, for resizing, evidently. It lists many, from fastest to slowest. I chose the slowest, because I figured it might do the best job with the resizing. Is there any truth to this, or is it simply just that...a faster vs. slower filter, without any quality repercussions?

 

I'm such a nerd. Geek_em8.gif

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This is great info Gary thumbs_up.gif

 

I usually aim to allow people with 800x600 screens to be able to see a whole image on the web, in a web browser. Thus for web pages I typically downsize my digital shots to 600x450 (or 450x600).

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MattP came up with a good term for digital darkrom work last night. If one needs to do that sort of work, the image is said to be "Yngve'd". As in, I got a nice shot of MattP last night at Pub Club, but his third eye did not show up clearly in the picture, so I Yngve'd it back in.

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Ken,

 

The FINE setting is usually the JPEG compression that the camera uses. It may have settings like NORMAL, FINE, SUPERFINE, UNCOMPRESSED. My recommendation is to use the best setting that is not UNCOMPRESSED/RAW, unless you specifically want RAW. Better quality means less noise/artifacts, but more larger files.

 

Regarding an external hard drive, here's a sweet gadget that's great for the field:

 

It doesn't need another computer to operate and runs off of batteries.

 

http://www.compactdrive.com/

A friend of mine has the PD70X with an 80G drive and is happy with it.

 

If you just want an external harddrive for a computer/laptop, there are much cheaper options. I just recently got a 250G external HD for $140 with a $50 rebate to knock it down to $90 from TigerDirect.com.

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Olyclimber,

 

When you save RAW, you are getting the pure data that comes off the CCD sensors. It is single-channel data (not RGB!) that is later converted into RGB via a demosaicking scheme (a CCD has color filters on it that go RGBGRGBGR...)

 

Other things the camera does in between the RAW image and compressing to JPG:

-white balance

-possibly mapping 10-12 bits down to 8 bits

-sharpening

-saturating

-other stuff

 

Saving as RAW gives you the power to do these yourself exactly how you want, but obviously that takes time. JPG does the stuff for you, and most of the time, the settings are right.

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VW4ever,

 

Resizing an image can happen in many ways. A full discussion involves interpolation and sampling schemes.

 

One simple example is suppose I had a checkerboard image where pixels alternate black and white. It's possible that with a simple (fast) downsampling scheme, a half-size image could end up all black or all white. A correct (slow) downsampling scheme should produce a half-size image that is all gray.

 

So yeah, pretty much fast is not as high quality, and when downsizing, the sorts of errors will be due to aliasing of high-frequency components.

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