Søk i denne bloggen og Lenker

onsdag 21. september 2011

BW Grain Experiments in GIMP for JPEG Images From the E450 Olympus DSLR

Black and white images out of the camera can be dissappointing, and even more so when they are "monotonised" or de-saturated from colour shots. There are several very comprehensive bloggs and chapters in books about getting effects which mimmick some of the classic photo journalist and artistic shots from the hey days of ilford fp5!

In this blogg I will offer a simplified, very quick approach to adding a corn or heavy grain effect to images. In the days of film, the grain was often caused by photographers "pushing" the negatives or prints to make a dark image captured at silly shutter speed, light enough to get in print. Alternatively, the enlargements were of a small area of the negative, or they used a small negative in the first place, like the original PEN crop onto 35mm.

Firstly you will need a texture background with an element of random grain and you can create these yourself at vast hassle or get one like the png file from http:byscuits.com ( it is a big file and will slow your browser down) grain-400tm.png. Dave Gandy has hosted this big png on behalf of the owner, and has this as a kind of traffic dirivng advertisement for visitors. Thank you both Petteri S, and Dave G . for allowing this to be shared.

This particular image has some "Hairs" on it and is actually quite a fine grain. It is like an ISO 400 film I beleive, and at that level of "push" in BW you don't get the real effect- a half way house between sharp, natural textrure and impressionable grain.

1) Open and Adjust the Grain Image to Corny-ness, size and Orientation.

So the thing to do is then open this in GIMP and then clip out a section to be rescaled and therefore have more visible corn. The grain 400 png is about a 20mpx scan, landscape so you need to go to a small crop in order to get a heavy grain effect for a 10mpx image in the case of the E450.

Open as the first image, clip to between 10 and 25% of the area with the tool to either portrait or landscape rough dimensions. Then use in the image pull down ( scaling layers does not work to scale the grain once you have two open). To super impose this grain on a landscape it is W3648 x2736 for the E450 at 10mpx jpeg, and conversely 2736 x 3648 portrait 90'.

At this point it is worth saving the grain crop scaled to 10mpx, and probably worth making a set of different grain densities in portrait or landscape orientation. PNG is fine, but an xcf layer ( gimp's own bitmap with extended information on process) is as good or it can be okay as a jpeg.

2) Open The Image You Want Grain / BW onto as a Layer

Gimp seems to detect that the png layer is monotone and converts the incoming jpeg from colour to BW automatically: but if it does not in your case / version /universe then you can just select that layer alone and choose - desaturate - from the colour pull down.

If it is not open already, use CTRL-L to open the layers dialogue box.

3) Adjust your image layer tonal curve

If you are au fais with using the tonal curve adjustment then you should adjust the contrast upwards in that way, and also see if there is some quality of the image to be gained in the individual R-G_B channels. If you are a simple mortal just into GIMP and no more, then use contrast slider until you like the image.

The image will lose a bit of contrast and brightens when the grain layer is merged in, so you need to experiment and make sure you are looking at the layers properly: image on top of grain background, both "eyes" on in the dialogue showing they are both visible when you want to see the combined effect, and only the image is visible when you adjust that alone.

3) Adjust opaicity or use - Grain Merge -

This is the reverse of transparency. 95% is then only 5% see-through. Adjust this using first the "Normal" selection in the mini pull down on the Layers Dialogue window.

As stated you will lose some contrast which you then have to compensate for, and you may eventually need to darken or lighten the grain layer in order to get the desired texture.

You can then experiment with all this, but GIMP has done much of the job for you in mergign texture without altering the contrast too much, employed via the same pull down, quite far down the list you will find " Grain Merge" and this instantly shows the merging of the texture to the image : it still does change the contrast, adding some white and grey quarter tone noise from the png file: but you can then adjust the curve of the image more subtely and see the result directly

3) Save An "xcf" File " Save a copy..."

when you are near finished, do this: it is worth doing underway too, so you can trace your work back. FOr example if it was the grain layer which really messed up the contrast

4) final adjustments.

Fine adjustments to the curves, any sharpening you feel you may want ( with threshold above 8 pixels so the grain is not "worked up"). In the byscuits grain png there is are abberations, notably hair lines which have white trails left on the image at some point in its processing.

5) Merge down and Save

Merge down is the final thing you need to do: when using GRAIN MERGE you get a perfect preview of the merge, while with semi opaque you can have an issue sometimes with final versus your impression from viewing the layers.

If you choose to save a copy now as a jpeg, then it will merge and export to jpeg., leaving you free to save as an xcf and also work backwards in "undo-s" if when in the cold light of day you hate it all!!

Ingen kommentarer:

Legg inn en kommentar