We all aspire to be published in Nature – but how many of us have actually read the policies set out by the Nature Group, particularly those relating to image integrity?
Most (if not all) journals have policies and guidelines on image integrity and it is worth becoming familiar with there before you do your experiments or acquire your images. Some of the policies refer to image acquisition practices, others require you to keep records of equipment settings – it is not always easy or even possible to do this retrospectively once to get close to submitting a manuscript.
I suggest you go and take a look at the Nature policies (most other journals will be similar) but in the meantime, here are some highlights:
“Authors should retain their unprocessed data and metadata files, as editors may request them to aid in manuscript evaluation.”
I can’t even begin to count the number of times a student or colleague has come to me asking for help with an image but has been unable to locate their original files. If they can’t find them for me then how will they find them when Nature’s editors request them? It is vitally important that you keep your original image files untouched (directly as they come from your acquisition software) and in a logical filing system so that you can find them, possibly years later, if required. There are any number of ways to achieve this and I’ll be investigating some of them in a later post but the most important thing is to develop a system and stick to it!
“All digitized images submitted with the final revision of the manuscript must be of high quality and have resolutions of at least 300 d.p.i. for colour, 600 d.p.i. for greyscale and 1,200 d.p.i. for line art.”
At least 300 dpi for colour images and even greater for grey-scale and line art! This is one that I have seen people get caught out by many times. It doesn’t matter how good your image is, if you have prepared it at a resolution of less than 300 dpi then it won’t be accepted. And if you can’t find your original files to redo the image (see above) then you are stuck. My advice is always work at the highest size and resolution your computing power will handle. Remember, you can always reduce the size and/or resolution of an image but it is impossible to increase resolution once it has been lost.
“Manuscripts should include a single Supplementary Methods file (or be part of a larger Methods section) labelled ‘equipment and settings’ that describes for each figure the pertinent instrument settings, acquisition conditions and processing changes, as described in this guide.”
Could you tell me the exact settings on the microscope for the images that you took yesterday? Do you know the exact degree to which you adjusted the contrast on your images last week? If the answer is no, then you are going to have trouble writing the required Supplementary Methods file. Before you dive in and start taking pictures, make sure you fully understand the workings of your equipment. Take a note of all settings (even those you don’t change as you never know if another user may change them between your sessions) and make sure you keep them consistent. Use your lab book to note the instrument settings each time you use it and make a note of things like exposure and gain for each image acquired. Some acquisition software will record this information for you and store it in the Exif data – if you rely on this then you will need to ensure that your original files are maintained with this data intact.
“The use of touch-up tools, such as cloning and healing tools in Photoshop, or any feature that deliberately obscures manipulations, is to be avoided.”
This one is a bit of a no-brainer to me but I have often been surprised by the number of researchers who think it is okay to use the touch-up tools as long as they aren’t changing the data. As far as I am concerned these tools should never be used on scientific images (well, almost never – there are some very specific cases where they may be useful but their use must always be very carefully considered). Unless you really know what you are doing and why you are doing it, steer clear of the touch-up tools.
“Processing (such as changing brightness and contrast) is appropriate only when it is applied equally across the entire image and is applied equally to controls.”
In an ideal world there would never be any need for post-processing scientific images. Your microscope and/or camera should be set to take perfect images in the first place. While this is the aim, it is not always possible to achieve so it is accepted that some level of post-processing is allowable. However you should always make sure that you process all your images (both experimental and controls) in exactly the same way. If you have a lot of images the best way to do this is by using Photoshop’s batch processing tool to apply the same manipulation to multiple images at a time.
I will be discussing this topic further in future posts but for now I have some questions for you:
- Have you ever taken the time to read journal’s image integrity policy before?
- Do you have a logical filing system that works – or one that doesn’t?
- Have you ever been caught out when trying to publish your work?