JPEG Commpression?

Thks Moggy

On this forum, it has been stated that every time, you open a jpeg file, you may loose some data. I am wondering what happens with jpegs files on CD and DVD which cannot be rewritten?

Every time you resave a jpg, not every time you open / view it.

Moggy

On this forum, it has been stated that every time, you open a jpeg file, you may loose some data. I am wondering what happens with jpegs files on CD and DVD which cannot be rewritten?

Right, after you take a shot with your 8m megapixel camera what’s your next step in Photoshop 7, just in case I’m doing it wrong (and I must be sometimes because some of the shots I take are just no good)
If some of you guys could post each step you all take after uploading your shots to the PC I’ll see if it’s something I’m just not doing right although I’ve got a feeling it’s to do with JPEG commpression? 🙁

A few general tips about digital photography. I personally use Photoshop (was brought up on it!), but I find that Paintshop Pro is just as good for many things and easier to understand and you can try it free). Use your camera to take some test shots and try the following

1) Always shoot the highest quality setting the camera will allow – it can be downsized later, but not upsized.

2) RAW mode does give higher quality, but the resulting image is up to 10 times bigger in storage size than Jpeg and the only real advantage is slightly better handling of very fine levels of brightness, contrast and colours – i think it is fair to say that many dedicated photographers have tried RAW and then gone back to high-quality JPEG as there is precious little difference. ( RAW is good for portraits and still-life subjects )

3) turn OFF any in-camera sharpening function if you intend to later use an image editing program – iphotoshop / will do a lot more precise job of sharpening the pic, Try the SHARPEN tool and the UNSHARP mask to see the difference they make

4) you can use the LEVELS function to correct brightness/ contrast in pics. Save a test pic somewhere on your PC that you don’t mind trashing and then play with the AUTO LEVELS function and MANUAL LEVELS function to see the difference they make.

5) when you save a Jpeg pic after altering, you may be asked how much compression to apply. 10 to 1 is the usual ratio as a good balance between quality and space. More than 10 to 1 will give a smaller file size, but reduced quality.

One trick worth trying is you want to reduce a file size (for web or e-mail) is to check the file properties for the number of unique colours and then reduce the colour count. You waste a lot of file space if you save an image as 64,000 or even 32,000 colours when the image doesn’t need this. It is often possible to reduce the file size by 50% or more without any noticeble difference, because you have removed non-visible fine shades from the image.

Last, but not least – make it a good pic in the first place. Library have many good books on photography techniques and topics on composition, lighting, exposure, depth-of-field etc as just as relevent to digital as film.

Happy snapping 🙂

Not at all… But this is a tutorial forum where it is reasonable to assume that some people will not be as overly knowledgable as you may be. To make sweeping generalisations more aligned with film photography than digital, as you did, does not help those who are wrestling with bringing digital imaging into their hobby (or career).

Andy

So telling everyone that you have to do 101 things to EVERY PICTURE you take to make them exceptable is ‘helping those who are wrestling with bringing digital imaging into their hobby (or career)?’

Surley you should be telling them that ‘any of these, or a combination of these can help you improve you digital image’..

If you read what SPT writes he uses phrases like ‘If required’ and ‘If nesassary’. Thats what you/we should be telling people….

If you read my threads I picked up on someone who said they did them to all his images regardless…..

I obviously hit a few nerves out there.

Not at all… But this is a tutorial forum where it is reasonable to assume that some people will not be as overly knowledgable as you may be. To make sweeping generalisations more aligned with film photography than digital, as you did, does not help those who are wrestling with bringing digital imaging into their hobby (or career).

Andy

I obviously hit a few nerves out there.

If you read my reply I did say ‘If you have to do all this to every photo’

Yes there are instances when it is nesassary to carry out some of these. At no time did I say that I have not used any of the procedures listed on this post. In fact I admit I have at sometime needed to do so to secure the shot desired.

But, do you crop every picture? (yes, I have hear off and used selective enlargement) Do you have to level the horizon every time? Do you have to remove dust spots every time?

Payload obviously miss-read my comment on sharpness. No I did not say I can assess or improve the sharpness by eye! With todays autofocus lenses you cannot get any sharper using the camera. Some professionals still pre-focus using there eyesight..

And Skymoster Thanks for the advice, But I make my living taking photographs and as yet none of my clients have complained…

Here’s my complete workflow based on about 8 weeks use of a Nikon D70s and assuming Photoshop 7 or higher as the image editor…

1. Shoot RAW using auto white balance and matrix metering. Aim for an exposure that pushes the histogram as far to the right as possible without clipping the highlights. Under sensible lighting conditions the D70s achieves this 90% of the time using matrix metering. Otherwise, slight under exposure is best so as to retain highlight detail.

2. Using RawShooter Essentials, edit the downloaded folder of images to weed out the duds and also rans. Be ruthless. Only proceed further with the very best. This process is easier if a week or so elapses between shooting and reviewing.

3. Process the selected images using RawShooter Essentials. Camera set white balance and auto exposure almost always give a good start. Set sharpening to zero. Use noise removal to taste. It is not often needed with D70s files shot at ISO 200.

4. Batch convert using Adobe RGB as the colour working space (assuming this is what you use in Photoshop or whatever); File type TIFF; Bit depth 16 bit; Quality maximum and check sharpening (even though this was set to zero in the processing).

5. In Photoshop the images will look a little low in contrast and slightly soft (or very soft if you use a Canon!).

6. Still in 16 bit colour depth, use a levels adjustment layer to set a black and white point and adjust the overall brightness to taste.

7. Use a second adjustment layer (Hue and Saturation) to modify colour saturation if desired. I usually add +10 master channel saturation to landscapes, but do not alter aircraft shots.

8. Make any other adjustments you think necessary, e.g. colour balance, all by means of adjustment layers.

9. Create a new image layer incorporating all your adjustments: Shift + Ctrl + Alt+ N + E. Duplicate this layer. Apply Gaussian Blur at a radius of 20 to this duplicate. Alter the blend mode to Soft Light and the layer opacity to 10% – 20% according to taste. This subtly increases contrast and colour saturation.

10. Flatten the layers and apply the Unsharp Mask as follows:
Convert Colour Mode to Lab Colour.
Select Lightness Channel.
Apply USM, Amount 20, Radius 50, Threshold 0.
Select Lab Channel.
Convert Colour Mode to RGB Colour.
This gives a beneficial increase to the image dynamic range.

11. Finally crop and sharpen to taste. There are various good sharpening routines widely described on the Internet. Most involve use of the Lightness Channel in Lab Colour Mode, but there are other interesting and valid alternatives, such as High Pass Sharpening. Luminous Landscape is a good source of such techniques.

If posting an image on this or other forums, do the necessary resizing and conversion to 8 bit colour depth and JPEG on a duplicate of the original. Remember that Photoshop has a very useful save for web option (File>Save For Web), which allows fine control of file size and image quality. Also ensure that images for web use are in the sRGB colour space (Image>Mode>Convert To Profile). Internet browsers are not colour space aware (unless you are running a Mac) and assume an sRGB colour space. As a consequence, images in the Adobe RGB colour space look flat and washed out.

All this may seem rather time consuming, but my aim is the very best possible image quality, and there is no short cut to this. The basic Photoshop workflow can be created as an Action and becomes much quicker, with no need to remember things such as the USM settings. Whole folders of images can then be processed relatively quickly.

Hope this is of some help and interest. Comments and suggestions welcome!

Cropping should be down to Composure..

Have you never had a selective enlargement made from a negative or slide? If you haven’t yourself, I’m sure you will at least admit to having heard of the concept? :rolleyes: Nothing different with digital.

And Sharpness is done by either your eyesight or through your Lens…

ALL digital SLRs deliver slightly soft images out of the box unless you ramp up the in-camera sharpness setting to the maximum. One of the reasons for this is that printed images need to be slightly softer than do images displayed on screens (e.g. on the web). Images viewed on computer screens, with their limited number of pixels, will look good at a certain sharpness setting whilst the same picture sharpened to the same level when printed will look slightly jaggy. Unlike with digital toy-cameras, DSLR manufacturers give photographers the choice, which necessitates some post processing for sharpness.

Brightness should controlled by your TTL or light meter…

Nope, see previous – similar reason regarding web versus print and again DSLRs deliver slightly flat images out of the box unless you ramp up the contrast settings to the maximum. Furthermore, digital has more lattitude than many print films and a slight underexposure is often desirable as details in the dark areas will be registered (whilst not blowing highlights) and this detail can be brought out during post processing much more effectively than you’ll be able to pull detail out of the dark areas of a negative or slide. Oh, and are you seriously trying to tell us that a print made from a negative will never have any exposure correction made to it. Or have you never heard of dodging and burning in the context of film-based darkrooms? 😮 Oh dear! 😮

SORRY GUYS…

If you have to do all this to every photo you take.. Then, You either need to change your camera, or learn how to take photographs properly….

I’m sorry too PDS – I think you need to learn a little bit more about digital photography… :rolleyes: 😉

Andy

If you have to do all this to every photo you take.. Then, You either need to change your camera, or learn how to take photographs properly….

1. Cant afford it. 2. Why? Digital enables me to take acceptable pictures without knowing anything. I dont have the money or time for courses. I have enough problems keeping up with my profession.

SORRY GUYS…

Please don’t take offence.. But

If you have to do all this to every photo you take.. Then, You either need to change your camera, or learn how to take photographs properly….

LOL, no offence taken. I do not do this with all photos. Just those that go onto jetphotos.net since they are my showpieces if you will.

How did you manage before Digital???

Quite miraculously, considering my camera (Pentax Espio 200 compact camera). Mind you, nothing ever got online. With my Sony F717 is only did a little editing (basically only leveling and sharpening) but looking back I can see that those photos for the most part can be improved.

Cropping should be down to Composure..

At times I shoot a photo from planes that are too far away to fill the frame completely. But since my camera has almost 6MP this is not a problem. By cropping I still get a full frame with the required 1024×768.

Brightness should controlled by your TTL or light meter…

Not sure what you mean with TTL. I do no have a light meter though, so that settles that.

And Sharpness is done by either your eyesight or through your Lens…

EYESIGHT!!!! My current glasses are -4,8 and -3,5. My new glasses, to be delivered two weeks from now, will be -4,5 and -3,25.

And as far as removing objects.. I think we have had this discussion before…

Yeah, let’s not start that again!

This is what I do:

1) level the horizon
2) crop the photo
3) resize the photo to 1035×780. When sharpening a photo you get a white line around the photo. This can be cut out later by leaving some margin at this early stage.
4) change colours/saturation. Just a very little bit to make the colours more lively.
5) change brightness and contrast to make the bits in the shadow more visible, and to make the overexposed bits somewhat darker (overexposed bits can never be saved completely though)
6) remove dust spots
7) unsharp-mark
8) selective sharpening if required
9) resize it down to 1024×768 (standard monitor size) or 1024×683 (standard print size). Both these sizes are regularly accepted at JP.net and airliners.net so cutting the heigth down makes no difference. Often it helps the image by removing background. Also, my camera shoots at 1024×683 size so using that size is just more convenient.
10) save the file using a compression of no less than 10 on a 1-12 scale (12 highest)

SORRY GUYS…

Please don’t take offence.. But

If you have to do all this to every photo you take.. Then, You either need to change your camera, or learn how to take photographs properly….

How did you manage before Digital???

Apart from re-sizing, the only thing I check is the levels, if you use the right settings, you will not have to adjust them.

Cropping should be down to Composure..
Brightness should controlled by your TTL or light meter…
And Sharpness is done by either your eyesight or through your Lens…
And as far as removing objects.. I think we have had this discussion before…

But now we are talking about a different subject to what was originally posted here.

I have been interested in the way some of you re-size your images… Thanks for that.

This is what I do:

1) level the horizon
2) crop the photo
3) resize the photo to 1035×780. When sharpening a photo you get a white line around the photo. This can be cut out later by leaving some margin at this early stage.
4) change colours/saturation. Just a very little bit to make the colours more lively.
5) change brightness and contrast to make the bits in the shadow more visible, and to make the overexposed bits somewhat darker (overexposed bits can never be saved completely though)
6) remove dust spots
7) unsharp-mark
8) selective sharpening if required
9) resize it down to 1024×768 (standard monitor size) or 1024×683 (standard print size). Both these sizes are regularly accepted at JP.net and airliners.net so cutting the heigth down makes no difference. Often it helps the image by removing background. Also, my camera shoots at 1024×683 size so using that size is just more convenient.
10) save the file using a compression of no less than 10 on a 1-12 scale (12 highest)

when it comes to reconstituting the image later as it is not always possible to “recover” the lost data.

It is never possible to “recover” the lost data. Once JPEG compression has thrown it away, you cannot get it back. That is why JPEG compression is never a good idea if image quality is your aim. I fail to see the point in spending large amounts of money on a 6MP or 8MP digital SLR only to shoot JPEG in camera, since the in camera processing throws away much of the quality advantage that buying 6 or 8MP gives you.

Finally, note that losses from compression are cumulative – resaving a jpeg over and over again will gradually make the quality worse.

Of course the answer to this is to always keep the original. When you’ve adjusted a picture, save it as a new image in a sub-directory – I usually have the originals at the top level, and create a subdirectory called “modified” or something, and save edited pictures in there. That way I can always start again. Takes up a bit more room, but hard drives and CDRoms are cheap these days.

Skymonster, on no4 creating a duplicate layer and applying the equalise filter to that layer can also give benefits as you can turn each layer on or off to compare. Surprised at no5 as well from a screener ;

Paul, I agree, that’s the one point when I do tend to create a layer sometimes. IMHO easier approach however is to clean the camera sensor!

As far as cloning out lamp posts etc is concerned (1) I’m not a photo screener at that other site anymore, (2) I do like to tidy up images but I draw the line at messing with the subject itself – I don’t do that and (3) what the eye can’t detect the brain doesn’t need to worry about – in other words, if you do the cloning well enough no one needs be aware you’ve done it 😉

Andy

Hey I use Picasa 2.0. There is abutton called ‘Iam feeling lucky’ which seems to amazingly transform a dull and dreary image to a better looking one..

what kind of normal operations does this button actually do?

It basically adjusts contrast, levels and color (sic)

I find it absolutely excellent for correcting shots out of the aircraft through the perspex.

Moggy

If using USM in photoshop I only set the % to around 50% and apply 2 or 3 times, rather than 1 pass with 150% set.

Also worth considering is to calibrate your own monitor as there can be a lot of difference. My home monitor is fine yet the pictures I put here always look on the dark side and can only put it down to calibration (or lack of) on work monitor.

Skymonster, on no4 creating a duplicate layer and applying the equalise filter to that layer can also give benefits as you can turn each layer on or off to compare. Surprised at no5 as well from a screener 😉

In PS there is a grid function which does help with getting the image horizontal.

Same as I do, Skymonster, except that I was taught to do the histogram at step 2.

Personally, I save the file as a bitmap and use MS Paint. Then do the image stretch and skew. Works well enough IMHO.

TNZ