Question for digital camera experts

[Dunderman]

My digital camera has a number of picture quality settings. The top two confuse me. They have the same resolution, but one is called "SHQ" and the other "HQ" (I assume they mean Super High Quality and High Quality, respectively). The memory stick can store 13 SHQ images and 40+ HQ images, so obviously there is a difference despite the resolutions being identical.

So I took two pictures of the same scene, one on the SHQ setting and one on the HQ setting, and compared them. Couldn't tell the difference. Zoomed in on the same part of the image until I could see the pixels. Couldn't tell the difference. Asked a friend to take a look. He couldn't tell the difference either. But the SHQ image is three times as big as the HQ image, so it's storing some kind of information. If it's undetectable by the human eye (I am, perhaps arrogantly, assuming that I and my friend are in possession of four typical specimens of that spectacular piece of equipment), then what good is it?

[Shalmanese]

HQ images will have more JPEG compression than SHQ ones. If you have access to photoshop, you can find the difference in pixels. If you're happy with HQ, then use HQ.

[Mangetout]

I expect the difference will be in the level of JPEG compression applied to the images; pick a high-contrast area of the image(s) - such as part that shows some black writing on a sign, or tree branches silhouetted against the sky - and zoom right in - the HQ image may show blocky artefacts around the high-contrast areas that may not be present (or may be minimal) in the SHQ image.

Some images compress better than others, so for the majority of pictures, you probably wouldn't notice - especially when you're viewing them at a fairly modest size - start cropping and zooming and the difference may become more obvious.

[Dunderman]

Originally Posted by Shalmanese

If you have access to photoshop, you can find the difference in pixels.

What do I do in Photoshop to see the difference? I couldn't tell in whatever I was using at my friend's computer.

Mangetout, I'll take two high-contrast images and zoom in to check. Just a moment... done. Tree branches against the sky. No, I seriously can't tell.

[Canadjun]

Unless you've got a very small memory stick it sounds like you have quite high resolution already since you said you can only store around 13 or 40 pics. If that's the case you'll probably need to use Photoshop or some other software to do some EXTREME zooming in of a high contrast image to clearly see the difference.

I'm no digital camera expert (I have one and have read quite a bit about them, but I don't claim to be an expert), but I'd suggest you probably only want to consider using your SHQ setting if you plan to get your pics blown up to poster size.

[Dunderman]

Originally Posted by Canadjun

Unless you've got a very small memory stick it sounds like you have quite high resolution already since you said you can only store around 13 or 40 pics. If that's the case you'll probably need to use Photoshop or some other software to do some EXTREME zooming in of a high contrast image to clearly see the difference.

I've already zoomed in so that the pixels are around 1cmx1cm on my screen and I can't tell the difference. Forgive me if I'm slow, but what could I possibly manage to see if I zoomed in more? What would show up that I can't see now?

[Shalmanese]

Take two identical pictures with different quality settings. Open both in photoshop, copy one on top of the other so that you have two layers. Right click on the top layer and select blending options and change the blend mode to difference. Flatten the layers and then use the brightness/contrast control to increase the contrast and make the differences more apparent.

[slaphead]

If you tell us the camera make and model, I'm sure one of us can spare a minute or two to find out the difference as per the manual.

[Mangetout]

That's more zoom than you need to be able to see compression artefacts in JPEG images, in fact, I'd say you have little chance of spotting them at that close a zoom.

You can only really diff the images in Photoshop if they are differently-compressed versions of the same original picture; two different pictures of the same scene, even when taken with a camera mounted on a tripod on a windless day, are still likely to have some differences between them.

Here is an image that shows the sort of thing that you might be looking for - it may be the case, though, that the HQ level of compression used by your camera is still perfectly adequate and is unlikely to introduce noticeable compression artefacts - in which case the SHQ level may just be overkill, but even if it isn't visibly noticeable, there are still occasions when a photo needs to start out as clean as possible - for example, when it will be subjected to further enhancement - as this can bring out small glitches that were always there, but weren't noticeable before.

Or it may even be that SHQ is being stored completely uncompressed

[Troy McClure SF]

Originally Posted by Mangetout

Or it may even be that SHQ is being stored completely uncompressed

That was my first guess. My camera can save three levels of JPEG, plus RAW and TIFF.

[ftg]

If you want to find compression artifacts, take pictures of very bland things. Jpeg compression is best on "real life" images that have a lot of barely noticable detail that can be cut out. So the more artificial the better. One of the tests I use for image quality is white on black background text. I then look at the edges of the letters for smoothness and lack of color fringes.

So go find a 2 color, high contrast sign. Stand about 6 feet away and take some pics.