Strange Red/Magenta Pattern in background!

[Svante]

Hi

Having a really hard time to get rid of the stange pattern when downsized from
170mb to 10mb!! Any super dupers out there that can help!!

Thanks

[John Wheeler]

Hi Svante and welcome to the forums.

Since your provided images are now also greatly compressed (down to 82KB) it is difficult to see the issue yet I can tell it is there (especially if I use a PS Hue/Sat Adj Layer and crank up the Sat)

Any more details that you can supply would help the forum members help you with suggestions e.g.

- Application and version that you are using
- Are you downsizing by just sampling down to smaller pixel dimensions or are you also doing any compression (e.g. JPEG)
- Are there any changes in color spaces involved?

If it is JPEG compression, I am not surprised by your results. There are some easy fixes such as brushing over the area with your desired color and set Blend mode for brush to Color (doing so on blank layer above original is preferred).

There may be alternatives yet you will need to provide some more details to get better suggestions.

[Svante]

HI John

Thanks. Im on Photoshop 12.0.4. OS 10.6.7.
Image of my macro, yet in Swedish. This has never happend to me before.
Yes i save the image in JPG(12). Adobe RGB 98 on both images.
This is my second job with the H4D-60. Before H3D-39.
Yet the high res looks nice, so it couldt be the cam.
What more alt. are u talking about?

/S

[mistermonday]

Originally Posted by Svante

Hi

Having a really hard time to get rid of the stange pattern when downsized from
170mb to 10mb!! Any super dupers out there that can help!!

Thanks

Did you downsize by using Photoshop's Image>File Size to resample the image, or did you downsize by saving as a jpg with a very low quality value in order to reduce the file size? The two different methods will give you different results. When you keep the same number of pixels but strongly compress a file, the software looks at blocks of adjacent colors and it decides that two colors are close enough that it will make them the same. Consequent a dark brown dot beside a dark red dot may both end up as one color or the other or something different than either. The lower quality setting you use (1-12), the worse things get. The process is also destructive and not reversible.
Regards, Murray

[John Wheeler]

Hi Svante

That is one fine camera.

I agree with everything the Murray has posted.

I am not sure of the root cause of the issue you are seeing. Pretty good chance that this is just an anomaly of the JPEG compression yet am surprised that at JPEG12 that we would see this issue. Also, based on the image and the content you apparently have just stored in JPEG to get to 10MB and have not changed your pixel dimensions (please confirm).

Here is what I would do in this order as an experiment:
- view both images at 100% flattened. Photoshop can produce artifacts when viewing both due to layer/masking effects and also just due to display anomalies viewing at sub 100%. If the issue goes away at 100% then this should not be an issue at print (Also it would be great if you could post a link to 100% views without additional compression to better see the issue)

- If the above does not resolve the issue also try a compression at JPEG11 as well and see if the issue goes away/changes. This does not solve your problem yet could help point to the JPEG compression if it does change.

- A very remote possibility is that you have some fine pattern we cannot see in the image background that resolves in the full image yet we cannot see in the very small/compressed image on the forum. If this pattern just happened to occur at the same frequency with how JPEG breaks up its squares for compression, then this can cause artifacts though pretty less likely. Does you background have a very smooth change or is there subtle pattern with which to be concerned?

- We probably need to see the results of the above questions yet a band-aid is to retouch the image. It would be much more desirable to get to root cause since it happened once, it will not doubt happen again.


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